SPECIES: Sorghum halepense

Choose from the following categories of information.

• Introductory
• Distribution and occurrence
• Botanical and ecological characteristics
• Fire ecology
• Fire effects
• Management considerations
• References

INTRODUCTORY

AUTHORSHIP AND CITATION FEIS ABBREVIATION SYNONYMS NRCS PLANT CODE COMMON NAMES TAXONOMY LIFE FORM FEDERAL LEGAL STATUS OTHER STATUS
	Craig Thornsen. © 2001, California Dept. of Food and Agriculture

DISTRIBUTION AND OCCURRENCE

• GENERAL DISTRIBUTION
• ECOSYSTEMS
• STATES/PROVINCES
• BLM PHYSIOGRAPHIC REGIONS
• KUCHLER PLANT ASSOCIATIONS
• SAF COVER TYPES
• SRM (RANGELAND) COVER TYPES
• HABITAT TYPES AND PLANT COMMUNITIES

In the United States, Johnson grass was introduced in South Carolina from Turkey around 1830. William Johnson, whom the plant is named after, established Johnson grass along the Alabama River in the 1840s as a forage species, and Johnson grass spread rapidly across the South [14,150,171,183]. Johnson grass is now widely escaped from cultivation in much of the United States. It is most invasive in the Southeast, although it is widespread in central California and New Mexico [123,129,207]. Johnson grass is not persistent in the Pacific Northwest, upper northern Great Plains, extreme northern portions of the Great Lake states, the Northeast [71,111,133,195], or in Arizona, Colorado, and Utah [112,201,202]. Plants database provides a state distributional map of Johnson grass.

Johnson grass occurrence is not well documented for all plant communities where it may occur. The following classification lists are not restrictive, but include plant communities where Johnson grass is a documented species.

Riparian and wetland associates: A vegetation survey on the lower Rio Grande of Texas found Johnson grass was the most common herbaceous cover (34%) in Fremont cottonwood-Goodding willow (Populus fremontii-Salix gooddingii) communities, followed by docks (Rumex spp.) (32% cover). Saltcedar (Tamarix chinensis ) and seepwillow (Baccharis spp.) were most common in the shrub layer [57]. On the Tensas River National Wildlife Refuge, Louisiana, Johnson grass is a dominant herbaceous species (8% cover) in winged elm-American elm-cedar elm-green ash (Ulmus alata-U. americana-U. crassifolia-Fraxinus pennsylvanica) woodlands. Other dominant herbs include purple loosestrife (Lythrum salicaria, 21% cover), trumpet creeper (Campsis radicans, 13% cover), and bushy bluestem (Andropogon glomeratus, 7% cover) [124].

Old fields: On old bottomland fields of the Mississippi and Yazoo rivers, Mississippi, Johnson grass cover is greatest on silty-clay loams. Associated overstory species are Texas red oak (Quercus texicana), Shumard oak (Q. shumardii), and cherrybark oak (Quercus  pagoda). Canada goldenrod (Solidago canadensis) is a common herbaceous associate [3]. In Oklahoma, Johnson grass dominates on bottomlands and old fields, associating with ragweed (Ambrosia trifida), Canadian horseweed (Conyza canadensis), and smooth sumac (Rhus glabra). Hoagland [96] provides a description of Johnson grass-dominated old-field communities in Oklahoma.

BOTANICAL AND ECOLOGICAL CHARACTERISTICS

GENERAL BOTANICAL CHARACTERISTICS RAUNKIAER LIFE FORM REGENERATION PROCESSES SITE CHARACTERISTICS SUCCESSIONAL STATUS SEASONAL DEVELOPMENT
	Entire Johnson grass plant (left), and Johnson grass rhizomes and culm shoots (right). Photos by Allan Kates, Virginia Polytechnic Institute (in [85]).

GENERAL BOTANICAL CHARACTERISTICS:
The following description of Johnson grass provides characteristics that may be relevant to fire ecology, and is not meant for identification. Keys for identification are available (e.g. [73,94,95,97,112,150,178,195]).

Morphology: Johnson grass is a nonnative, warm-season perennial [50,72,123,185,202]. It is usually rhizomatous, but is a highly variable species with many ecotypes [97]. It may grow as an annual in hot, arid climates and at the northern limits of its range [62,198,199]. Johnson grass rhizomes form a dense, tangled, tough sod [205]. Rhizomes serve as carbohydrate-storing and regeneration organs [6]. Most rhizomes occur in the top 7.9 inches (20 cm) of soil, although rhizomes in soft, deep soil may extend deeper [43,97]. Rhizomes vary in size from a few inches to several feet in length, and in thickness from 0.25 to 0.75 inch (6.4-19 mm) [87]. Leaves and aboveground stems (culms) are coarse [150]. Culms are 1.6 to 4.9 feet (0.5-1.5 m) tall. In flower, total plant height may reach 12 feet (3.7 m) [5]. The inflorescence is a 4- to 24-inch (10-60 cm) open panicle.  Spikelets of Sorghum species are paired: 1 is sessile and perfect; the other spikelet is pedicelled and staminate. Spikelets are 4 to 7 mm in length. There are about 35 to 350 spikelets per panicle, depending upon ecotype. Lemmas are cilate; they may be awnless or have short (1-15 mm), sometimes twisted awns that aid in seed dispersal [50,71,94,123,185,195,197,202]. Seeds are about 2 mm long [150].

Physiology: Several physiological characteristics of Johnson grass aid in its spread. Mature Johnson grass plants are moderately drought resistant [6] and salt tolerant [208]. Johnson grass produces toxins (see Toxicity) that may be allelopathic [97,136,197].

Asexual regeneration: Once a population is established, most population growth is from asexual regeneration by rhizomes [97]. Throughout most of its North American range, Johnson grass populations are strongly rhizomatous [50,72,123,185,202]. Some Johnson grass populations are weakly rhizomatous or nonrhizomatous, especially at the species' distributional limits [62,198,199]. Rhizome expression in Johnson grass is apparently controlled by multiple, dominant genes, resulting in variable degrees of rhizome development in both Johnson grass and its hybrids [210]. Extreme temperatures also inhibit Johnson grass' ability to produce rhizomes [86,176].

Rhizome development: Johnson grass plants begin growing rhizomes in the seedling stage. Primary rhizomes are initiated at the 5-leaf stage, when plants are about a foot tall. Rhizome growth continues slowly until the 10-leaf stage, then accelerates greatly. Rhizomes are well developed by 6 to 7 weeks [6,102,126]. In a greenhouse experiment, Anderson and others [6] noted extensive rhizome development on 4.5-month-old plants, with over 5,200 rhizome nodes/plant [6].

In older plants, last-year or primary rhizomes produce new, secondary rhizomes in spring. Secondary rhizomes in turn produce tertiary rhizomes. Secondary and tertiary rhizome growth slows or stops around flowering, then resumes with seedhead development [127]. Rhizome production peaks at seed ripening [79,98], when a single plant may produce 200 to 300 feet (60-90 m) of rhizomes [128]. Secondary and tertiary rhizomes continue growth and carbohydrate accumulation until late fall, then go dormant over winter. Primary rhizomes die each fall. In spring, secondary and tertiary rhizomes become current-year primary rhizomes [4,43,81,87,97,102].

Rhizome sprouting: Small or broken rhizomes, especially secondaries, can form new plants [6,9,43,174]. Plows spread Johnson grass by breaking up, dispersing, and replanting rhizomes [3] (see Cultural control). Small rhizomes are more likely to sprout when shallowly buried, while large rhizomes are more likely to sprout when deeply buried. In the greenhouse, 3-inch (7.6-cm) rhizome sections sprouted best when planted less than 3 inches deep. Longer, 6-inch (15.2-cm) sections sprouted best when buried deeper than 3 inches ([39] and references therein). In a Mississippi field experiment, McWhorter [126,127] found that with shallow burial (< 2 inches (6 cm)), short rhizomes (< 3 inches (7.6 cm)) produced more sprouts than long rhizomes (6 inches (15.2 cm)). The opposite trend occurred when rhizomes were planted deeper than 2.4 inches (6 cm). Rhizomes usually grow to a depth of 10 to 20 inches (25-50 cm) [128]. Loose, sandy or loamy soils generally allow for best rhizome expansion [127]. Clay tends to inhibit rhizome expansion [87]; however, rhizomes may penetrate several feet down cracks in clay soil [127]. Deeply buried rhizomes that do not sprout cannot survive more than a year [4,81,97].

Rhizomes are somewhat drought-resistant, remaining viable after drying to 40% of initial harvest weight [6]. They are sensitive to extreme temperatures. In northern climates, rhizomes must be deeply buried in order to overwinter. In an Illinois field experiment, Johnson grass rhizomes did not survive winter temperatures less than 1.4 °F (-17 °C) unless buried 7.9 inches (20 cm) or more below ground [176]. In southern Ontario, rhizomes must be 10 inches (25 cm) or more inches below ground to overwinter ([86] and references therein).

Sexual regeneration: Although growth of established populations is primarily through rhizomes, Johnson grass expands its distribution and establishes new populations through seed spread [97].

Breeding system: Sorghum species are mostly self-crossed, although some outcrossing occurs ([197] and references therein).

Pollination: Johnson grass is primarily self-pollinated [197]. Some pollination is effected by wind, especially when plants are < 425 feet (130 m) apart [197,203].

Seed production: Johnson grass is a short-day plant, requiring 8 to 16 hours of daylight to flower [67,136]. It is a good seed producer under favorable growing conditions. A single plant may produce 80,000 or more seeds in 1 growing season [3,85]. Two seed crops may be produced under good conditions. In agricultural fields in Argentina, Johnson grass produced a large seed crop in early summer (Jan-Feb.; 60% of total seed production for the year) and a smaller seed crop in late summer-early fall (mid-March-early April; 40% of annual seed production) [67]. Johnson grass seed production is estimated at 90 gallons/acre (855 L/ha) on good sites in the South. Field trials in Mississippi showed mean seed production of 84 g/plant and 28,000 seeds/plant [128,197]. Resources are allocated to rhizomes at the expense of seeds under poor growing conditions [22,23].

Greenhouse trials using Johnson grass seed from the Northeast showed populations that grow and reproduce as annuals have faster growth rates, more rapid development, more and larger seeds, and fewer rhizomes compared to populations that sprout from overwintered rhizomes [199].

Seed dispersal: Wind, water, machinery, and animals disperse Johnson grass seed [3,66,85,86,183]. Spikelets are readily deciduous [202] and usually disperse as a unit beneath the parent plant [3,66,71,73]. Strong winds disperse seed longer distances. In Argentina, 28- to 31-mile/hr (45- to 50-km/hr) winds that occurred during May thunderstorms carried Johnson grass seed 2,950 to 3,300 feet (900-1,000 m) from parent plants [66]. Water has dispersed seed along many waterways of the United States [3,85,183]. Farming equipment also spreads seeds [66,85]. Viable Johnson grass seed is a common contaminant in hay, harvested crops, and commercial seed [3,143]. Johnson grass seed retains viability after passing through the digestive tracts of livestock [9,85,127]. The relative importance of agents that disperse Johnson grass seed is unclear [129].

Seed banking: Johnson grass builds up a soil seed bank [190]. The seeds are dormant and may remain viable for several years, although most soil-stored seeds germinate in their 1st or 2nd year [3,97,136]. In Mississippi, 1st-year stratified seed showed 82% viability in the field. After burial in the field for 2.5 years, the same seed lot showed 62% viability [54]. In California, 5-year-old buried seed showed > 50% viability, but by age 6, viability dropped to 2% [121].

Germination: Johnson grass has 2 mechanisms of dormancy: mechanical dormancy imposed by the seed hull and seedcoat, which requires weathering or scarification to break; and chemical dormancy, which requires oxygen to break [101]. Diurnal fluctuations in temperature, afterripening, or both are needed to overcome both types of dormancy [26,26,65,100,182]. Seed from water-stressed plants is generally less dormant than seed from amply watered plants [23]. Benech and others [25] present a model predicting loss of seed dormancy and consequent seedling emergence based on soil temperature.

Light improves germination rate with warm temperatures (> 93 °F (34 °C)) and inhibits germination with cold temperatures (< 72 °F (22  °C) [101]. In the greenhouse, Taylorson and McWhorter [182] found a 63% increase in germination rate for Johnson grass seed exposed to light vs. seeds kept in the dark. Deeply buried seed remains dormant for at least 7 years [85], but does not germinate [27,65,100]. Soil upheaval such as cultivation, which brings seed closer to the soil surface, usually increases germination rates [65,100]. In the greenhouse, best germination (60-75%) occurred with surface-scattered to shallowly buried (0-1.6 inches (0-4 cm)) seed. Less than 5% germination occurred with seed buried > 3 inches (8 cm) below the soil surface [27]. Litter cover or shallow burial may aid germination in the field. Prostko and others [148] present a model to predict Johnson grass seedling emergence based upon temperature and seed burial depth.

Seedling establishment/growth: Best establishment occurs on open, disturbed sites. Seed dispersed away from parent plants may show better establishment compared to seed falling beneath its parent. In an old field in Argentina, most Johnson grass seed fell near parent plants on undisturbed plots. Only 1% of seed beneath a parent plant established. On tilled plots mowed every 1-2 weeks by a corn (Zea mays) harvester, seed was carried 3 to 82 feet (1-25 m) from parent plants. Recruitment of those seed neared 100% [66]. On favorable sites, plants may produce 80 or more culms in their 1st year [3].

As a facultative annual, Johnson grass shows variable ability to regenerate from seed. Johnson grass annuals in rural-interface wildlands of southern Arizona rarely reproduce either from on-site seed or from rhizomes. Seed dispersed from adjacent agricultural lands provide continual sources of seed [62]. However, some populations in the northern portion of Johnson grass' range successfully reproduce from seed. In southern Ontario, northern Ohio, and northern New York, annual populations have larger leaves, inflorescences, and seeds compared to perennial Johnson grass populations [199].

Johnson grass seedlings may show faster 1st-year growth than plants started from rhizome fragments. On the Mississippi Delta near Stoneville, Mississippi, Johnson grass started from seed showed greater biomass and more rapid height gain than plants started from rhizome pieces. At flowering, seed plants were producing 0.75 to 3 feet (0.23-0.9 m) of new rhizome growth per day. Plant growth patterns were as follows (data are means) [126]:

Biomass and height of Johnson grass seedlings
Date (1959)	Days after emergence	Green weight (g)				Height (in)	Rhizome length (ft)
		Leaves	Rhizomes	Roots	Seedhead
May 20	20	12	2	3	----	12	----
May 27	27	190	30	30	----	23	<1
June 15	46	690	90	100	----	52	7
July 1	62	1990	750	220	180	74	35
Sept. 1	124	2950	5050	360	500	74	153
Sept. 29	152	3140	8070	430	680	74	212
Biomass and height of Johnson grass rhizome sprouts
May 20	19	9	3	3	----	9	----
May 27	26	80	14	20	----	13	<1
June 3	33	530	100	40	----	30	1
June 15	45	610	110	130	----	47	5
June 19	49	590	310	160	9	70	9
June 24	54	950	220	160	74	72	14

SITE CHARACTERISTICS:
Johnson grass is most common on disturbed sites such as ditch banks, roadsides, fields, and "waste places" [94,112,150,201]. It occurs on all soil textures [87], with best growth occurring on silty bottomland soils [3,87]. On old bottomland fields of the Mississippi and Yazoo rivers, Mississippi, Johnson grass cover is greatest on silty-clay loams [3].

Moisture regime: Although Johnson grass occurs in wet to dry habitats in its native range in southern Europe [185], in the United States it is generally restricted to wet or mesic sites [73,94,202]. It is most common in warm, humid southern climates that receive ample summer rainfall. Johnson grass is a facultative wetland species, frequently occurring on floodplains [18,19]. Johnson grass patches are often extensive along canals and irrigation ditches [97]. In arid sites such as Organ Pipe Cactus National Monument, Arizona, Johnson grass establishes mostly in wet locations such as washes, drainages, and stream edges [62,179].

Elevational ranges of Johnson grass in several states are:

Old fields: Johnson grass is particularly common on old bottomland fields in the South [3,17,18]. Unlike most crop weeds, which tend to decrease in the absence of irrigation and fertilization, Johnson grass tends to persist on abandoned fields. For example, in Georgia it was prevalent in 1-, 4-, and 8-year-old fertilized crop fields, but was also prevalent in 8-year-old fallow fields [140].

Shade tolerance: Johnson grass requires open sites and does not persist under closed canopies [78,191]. In a honey mesquite (Prosopis glandulosa) Texas savanna, Johnson grass associated with Texas wintergrass (Nassella lecotricha) in open areas, but was not found under honey mesquite or other trees [191]. In Argentina grasslands, canopy removal increased Johnson grass germination and establishment compared to closed-canopy sites [25].

Johnson grass produces seed about 2 months after initiation of spring rhizome expansion [152]. Even 1st-year Johnson grass plants are capable of quick flowering and seed set: Plants in Mississippi initiated flowers 46 days after seedling emergence [126]. Bridges and Chandler [35] present a model for predicting Johnson grass flowering under fluctuating field temperatures, with nitrogen fertilization, and with irrigation. Holshouser and Chandler [98,99] provide temperature-dependent models for predicting flowering, germination, rhizome bud break, and rhizome sprouting under field conditions.

The following table shows phenological development of Johnson grass in various states and regions:

FIRE ECOLOGY

• FIRE ECOLOGY OR ADAPTATIONS
• POSTFIRE REGENERATION STRATEGY

Little documentation is available on postfire regeneration of Johnson grass from seed. As a seed banking species that establishes in open, disturbed sites [72,84,170], it is likely that Johnson grass is capable of postfire seedling establishment. Information is needed on Johnson grass' ability to establish from seed after fire.

Fuels: Johnson [108] provides a model for estimating live:dead fuel ratios of Johnson grass. In Alabama wildlands, dry-matter biomass production of Johnson grass averaged 11.2 Mg/ha, more than most associated grasses [151]. Johnson grass litter reportedly remains on the ground through 1 or more growing seasons [105].

Fire regimes: Johnson grass is well adapted to survive under all fire regimes (understory, mixed, and stand-replacement). As of this writing (2004), there is no published information on how Johnson grass interacts with North American fire regimes. In riparian and other areas where Johnson grass is highly productive, Johnson grass may promote fire spread by increasing fine fuel loads above historic levels. Studies are needed on the fire ecology of Johnson grass in North American.

The following table provides fire return intervals for plant communities and ecosystems where Johnson grass may be important. For further information, refer to the FEIS review on the dominant species listed below.

FIRE EFFECTS

• IMMEDIATE FIRE EFFECT ON PLANT
• DISCUSSION AND QUALIFICATION OF FIRE EFFECT
• PLANT RESPONSE TO FIRE
• DISCUSSION AND QUALIFICATION OF PLANT RESPONSE
• FIRE MANAGEMENT CONSIDERATIONS

Very high temperatures kill Johnson grass seed. Soil-stored seed is protected from fire damage [132]. Fire scarification appears to have no effect on rate of seed germination. In the laboratory, there were no significant differences in rates of germination between unheated Johnson grass seed and seed heated to 200 °F (90 °C) and 400 °F (200 °C); mean germination rate was 52%. Mean germination rate dropped to 17% at 660 °F (350 °C) and 0% at 800 °F (430 °C) [132].

Published information on postfire seedling establishment of Johnson grass is lacking. Studies are needed on the ability of Johnson grass to establish from seed in postfire environments.

Spot burning with a gas torch was once a widely practiced method of controlling patches of Johnson grass. It is rarely used today due to cost restraints [128], but may be useful in riparian or other areas where spot control is needed. In Arizona, a Johnson grass infestation along a canal bank was controlled by torching plants with a propane burner. Eleven burnings at 2-week intervals were required until postfire sprouting stopped. Johnson grass was absent from the site the following year [87].

MANAGEMENT CONSIDERATIONS

• IMPORTANCE TO LIVESTOCK AND WILDLIFE
• OTHER USES
• IMPACTS AND CONTROL

Palatability/nutritional value: Johnson grass is moderately palatable and nutritious [48,50]. Deer make light to moderate use of Johnson grass [115,164], grazing all aboveground portions of the plant [48]. Rodents also graze Johnson grass. In honey mesquite (Prosopis glandulosa var. glandulosa) plains of Texas, Heerman's kangaroo rat and Great Basin pocket mouse used Johnson grass frequently (6.7% volume, 61% frequency; and 5.9% volume, 36% frequency, respectively) [2]. Quail, geese, and wild turkey consume Johnson grass seeds [31,48].

Although intolerant of heavy grazing, Johnson grass is a good pasture grass and makes fair-quality hay when cut in the boot stage [171,192]. Livestock make moderate to good use of fresh Johnson grass [88,92]. In a comparison of Texas range grasses, Johnson grass showed greatest in-vitro digestibility (45%-69%, depending on the digestion media) of 5 grasses tested [117]. Dairy cattle in Alabama showed good weight gain and milk production on Johnson grass pasture [88].

Nutritional content: In a western Texas study, Johnson grass had highest summer crude protein content (13.2%) of 9 rangeland grasses. Spring, fall, and winter crude protein values were 6.62%, 8.06%, and 3.81%, respectively [37]. In a greenhouse study comparing relative mineral content of 15 grass species, Johnson grass scored significantly higher (p=0.1) in phosphorus content than other grass species. Cobalt, manganese, and copper contents were moderate compared to other grasses [29]. Energy value of Johnson grass grown in Texas was 3,900 kcal/g [137]; in India, seasonal fluctuation in energy value varied from 3,684 kcal/g in October to 4,578 kcal/g in April [168]. Nutritional content of fresh Johnson grass in eastern Texas was [63]:

Seasonal changes in forage quality of Johnson grass on the Edwards Plateau of Texas were [104]:

When harvested at its peak, Johnson grass makes fair-quality hay, similar to timothy (Phleum pratense) hay in nutrient content [147]. In a 1928 study in an Alabama coal mine, draft horses and mules were fed oat (Avena sativa) grain and either Johnson grass or timothy hay for 3 months. The equines maintained their weight on both diets under "moderate" workloads. The animals lost weight on both diets under "heavy" workloads, but lost less weight on timothy hay and grain compared to Johnson grass hay and grain (mean losses of 10.71 and 21.78 lbs., respectively). Digestible nutrient means were [76]:

Toxicity: Johnson grass is generally a good forage grass [31,48,88,92]. However, at certain developmental stages or under some adverse environmental conditions, Johnson grass may form cyanogenetic glycosides that can poison livestock. Phenologically, Johnson grass is most toxic when leaves and culms are actively growing. Seedlings and sprouts generally have higher levels of glycosides than plants that have reached the flowering stage. Secondary growth, produced after mature plants are mowed or heavily grazed, can also have high levels of glycosides. Environmentally, Johnson grass is most toxic after drought, extreme heat, frost, or when plants are wet with dew or light rain. Glycoside levels can vary considerably among Johnson grass populations. Ruminants, especially cattle, are more susceptible to glycoside poisoning than monogastric herbivores like horses  [158,174]. As well as fresh plants, hay cut when Johnson grass is young or experiencing adverse environmental conditions such as drought can also be toxic [40,82,134,171,171]. Livestock poisoning can be prevented by waiting until new growth is 15 to 18 inches tall (38-46 cm) tall after drought, or deferring grazing until plants have dried after frost [129].

Johnson grass may sequester selenium (or other elements that are toxic at high doses) when growing in soils with high concentrations of toxic elements. In the Dead Sea area of Jordan, for example, selenium concentrations in Johnson grass samples were high enough to poison livestock [1].

Prolonged consumption of fresh Johnson grass can cause nitrate poisoning in ungulates [40,174]. Most livestock can graze Johnson grass safely when plants are at least 18 inches (46 cm) tall [171].

Cover value: No information is available on this topic.

Little is documented on Johnson grass' impact in wildlands, and further research is needed on how Johnson grass affects wildland habitats. Generalizations about Johnson grass must always be qualified because of numerous ecotypes [126]. Typically, Johnson grass is a good competitor for nutrient [97,197], space [104], and water [167] resources. It can outcompete associated species for water by extracting water from lower soil profiles (12 inches (30 cm) or more below ground) [106]. Johnson grass may also negatively impact plant community composition through its reputed allelopathy [97,136,197]. Cyanogenetic glycosides and other toxins in Johnson grass may inhibit germination and growth of associated plant species [97,136,197].

On many sites in the United States, Johnson grass is not invasive in undisturbed wildlands, although it may readily invade disturbed sites (Cox, as cited in [136]). Johnson grass is most invasive on moist sites in wet-temperate regions of the southeastern United States [72,73,136]. For example, Johnson grass and Canada thistle (Cirsium arvense) are listed as the 2 most invasive and expensive to control weeds on the Eastern Neck National Wildlife Refuge, Maryland [45]. Johnson grass interferes with conifer seedling establishment and growth on southern pinelands [51], and may interfere with cottonwood (Populus spp.) and willow (Salix spp.) establishment in riparian zones [172].

Johnson grass is not invasive on most sites in the Southwest. At the turn of the last century, Johnson grass was planted in southwestern arroyos and stream channels to stabilize soil [47]. It established on such wet and mesic sites, but failed to spread. Felger [62] reports Johnson grass as only weakly invasive in Organ Pipe Cactus National Monument, Arizona, where the arid climate restricts Johnson grass to roadsides and washes. Johnson grass may grow as an annual, without spreading, in arid southwestern wildlands. Nearby agricultural lands are continual seed sources [62].

Control: Although considerable information is available on controlling Johnson grass in agricultural settings (e.g., see [9,81,85,128,181]), information on controlling Johnson grass in rangelands, natural areas, and other wildlands is lacking. The following information on Johnson grass control is extracted primarily from agricultural literature but may be applied to some wildland settings, particularly old fields. Research is needed on controlling Johnson grass in wildland settings [136].

Johnson grass control involves several steps: 1) preventing seed from ripening and dispersing, 2) killing seedlings, 3) killing existing rhizomes, and 4) preventing growth of new rhizomes [9,81,85,128,181]. Control is most effective before plants have developed 5 leaves [102]. Detailed Johnson grass control procedures and techniques are given in several publications [97,128,136].

Prevention:  The most efficient and effective method of managing invasive species such as Johnson grass is to prevent their invasion and spread [165]. Preventing the establishment of nonnative invasive plants in wildlands is achieved by maintaining native communities and conducting aggressive surveying, monitoring, and any needed control measures several times each year. Monitoring efforts are best concentrated on the most disturbed areas in a site, particularly along potential pathways for Johnson grass invasion: roadsides, waterways, and old fields. Large plant size makes monitoring Johnson grass relatively easy in summer, and yearly summer monitoring helps managers assess the effectiveness of control programs. As of this writing (2004), monitoring programs for Johnson grass are in their infancy. As potential contact sources, Newman [136] provides a list of managers who have started monitoring programs for Johnson grass on Natural Areas. The Center for Invasive Plant Management provides an online guide to noxious weed prevention practices.

Integrated management: A combination of complementary control methods may be helpful for rapid and effective control of Johnson grass. Integrated management includes not only killing the target plant, but establishing desirable species and discouraging nonnative, invasive species over the long term. Johnson grass control is rarely successful with only 1 method of control [142], but a combination of control methods can be effective. For example, in a tallgrass restoration study on the Hear Wildlife Sanctuary, Texas, a combination of early fall glyphosate spraying followed by late fall tillage helped control nonnative grasses on a former Johnson grass-Bermuda grass (Cynodon dactylon) pasture. Early fall spraying targeted Johnson grass while it was still actively growing. After spraying, rhizomes brought to the soil surface by tilling 4 to 6 inches (10-15 cm) deep were killed by winter frost. Johnson grass showed 4.2% cover and 50% frequency 3 years after treatments. Only trace amounts of Bermuda grass were present [173].

Fire: See the Fire Management Considerations section of this summary.

Biological: Biological control of Johnson grass is problematic, as known control agents that kill Johnson grass also kill crop grasses such as corn and sorghum [129,144,146]. As of this writing (2004), there are no biocontrol agents approved for Johnson grass [184]. Several biological agents are being tested for possible use. A smut (Sphacelotheca holci) has helped control Johnson grass in Louisiana croplands [131]. In Florida field trials, a mixture of native fungal pathogens controlled Johnson grass and other weedy grasses in citrus (Citrus spp.) groves [44].

Heavy grazing over 2 or more years reduces Johnson grass by depleting rhizome reserves [3,8,90]. Rhizome development is greatly reduced when plant height is kept below 12 to 15 inches (30.5-38 cm) [128]. Best control is offered when herbicide or winter plowing treatments follow grazing treatments [3]. For example, in an unpublished study at the Patagonia/Sonoita Creek Preserve, Arizona, cow and horse summer grazing reduced density of Johnson grass. After 4 years of summer grazing, Johnson grass stem density had decreased 75% compared to pretreatment levels. Plots were then sprayed in late spring with glyphosate. Posttreatment restoration plantings gave mixed results. One to two months after spraying, native bunchgrasses were transplanted onto the study sites. Broadleaf weeds invaded the study plots after Johnson grass density was reduced by the grazing and herbicide treatments. After mowing treatments to control the broadleaved weeds, native bunchgrasses on some test plots are showing good growth. Other plots have experienced Johnson grass reinvasion and pocket gopher herbivory, to the detriment of native bunchgrasses. Preserve managers are continuing weed control treatments to promote the native bunchgrasses [184].

Geese are sometimes used for Johnson grass control in croplands. Geese prefer young shoots, and do not graze Johnson grass over about 7 inches (18 cm) in height [9,87].

Chemical: Herbicides may provide initial control of a new invasion or a severe infestation, but used alone, they are rarely a complete or long-term solution to invasive species management [41]. Herbicides are most effective on large infestations when incorporated into long-term management plans that include replacement of weeds with desirable species, careful land use management, and prevention of new infestations. Control with herbicides is temporary, as it does not change the conditions that allowed the invasion to occur in the 1st place (e.g. [212]). See The Nature Conservancy's Weed Control Methods Handbook for considerations on the use of herbicides in Natural Areas and detailed information on specific chemicals.

The most effective chemical control of Johnson grass involves using systematic herbicides that translocate the active chemicals to rhizomes [128]. A single application of herbicide generally does not control large infestations, and follow-up measures are needed for long-term control [170]. Johnson grass control can be obtained using glyphosate [7,21,105,128], phenoxy (e.g., 2,4-D, fluazifop), [109,116], or halogenated aliphatic (e.g., dalapon) herbicides [8,87,128]. Spot spraying with sodium chlorate [83,87] or dalapon has been effective for small infestations [154]. Spot control is not effective in the long term unless surrounding seed sources are also eliminated [105]. Experiments in agricultural fields in Argentina showed best control when the herbicide (dalapon) was applied when rhizome biomass was low. Ghersa and others [68] provide a model for predicting optimal spraying time based on minimum rhizome biomass. Although based on South American seasons, the model is easily adjustable for use in the northern hemisphere.

Postemergent herbicides are the most common method of Johnson grass control in agricultural systems, and are probably the best herbicide choice for wildland settings as well, since postemergent herbicides cause less damage to nontarget species. In a Maryland old-field study, foliar application of postemergence herbicide (DPX-V9360) was more effective in late-growth stages (> 5 leaves) than early-growth stages (< 5 leaves) when rhizomes had not fully expanded [139]. Rosales-Robles and others [159] discuss the relative effectiveness of several postemergent herbicides as influenced by application rate and Johnson grass growth stage. Application procedures for postemergent herbicides effective on Johnson grass are given in these publications: [20,52,120,209].

Ecotypes may show differential response to herbicides [129]. Populations in Kentucky and Mississippi show genetic resistance to fluazifop and other phenoxy herbicides [15,138,169]. Virginia populations have resistance to enzyme acetyl-coenzyme A carboxylase inhibitors [33]. In Greece, some populations show resistance to glyphosate [114].

Herbicide treatments greatly decreased Johnson grass cover in an Illinois bottomland old field. Restoration treatments included tillage, pre- or postemergent herbicide applications (sulfometuron or glyphosate, respectively), and green ash (Fraxinus pennsylvanica) plantings. Tillage had no significant impact on Johnson grass cover. Mean Johnson grass cover (%) was significantly lower after the 1st postspray year [77]:

Cultural: Little information is available on cultural methods of control for Johnson grass. An Arizona study using integrated pest management, including native bunchgrass plantings, showed some success in controlling Johnson grass (see grazing in the Biological control section above). Additional studies incorporating cultural control of Johnson grass are needed.

Physical/mechanical: Johnson grass can be controlled by tilling, mowing, and flooding [6,128,170]. Individual small plants or small clumps may be controlled by hand-pulling or solarization [13,55,170].

A consistent tillage program may provide effective control [6,43,81,126]. Unfortunately, tilling is not practical on most wildlands due to damage to desirable native plant species, uneven terrain, erosion, and cost constraints [105]. Tilling can be used on some sites such as bottomlands and old fields. Shallow plowing helps control Johnson grass by breaking up rhizome systems, exposing rhizomes to the sun or killing frosts, and depleting carbohydrate reserves [6,43,81,126]. Optimal plow depth is 8 to 12 inches (20-30 cm). Several treatments are needed in hot climates [87,102]. Killing sprouts early, before they form 5 leaves and start developing new rhizomes, gives best control [102]. First plowing is in spring (May), followed by similar plowings every 3 weeks (in rainy weather) to 6 weeks (in dry weather). New plants should reach more than 12 inches (30 cm) before plowing again [9]. In cold climates, Johnson grass is plowed in late October to expose rhizomes to frost [19]. An exposure of 24 or more hours to temperatures below 25 °F (- 4 °C) kills rhizomes [81,103,126,127]. A single plowing, or long intervals between plowings (> 4 years), is generally not effective because it stimulates growth [105,171], buries and protects rhizomes [43], and exposes deeply buried seeds to upper soil levels where they may germinate [65].

Because rhizomes may extend more than 20 inches (51 cm) below ground, cultivation alone may fail to kill Johnson grass rhizomes [43]. After plowing, close grazing or mowing (so that the grass stays < 12-15 inches (30-38 cm) tall) helps further reduce Johnson grass cover [87].

Even on old fields, tilling is a major soil disturbance that provides a favorable seedbed for pioneer species. Unless further rehabilitation efforts that include planting native herbaceous species are taken, it is likely that tilled fields will succeed to other invasive nonnatives.

Repeated, close mowing has the same inhibitory effect on growth as grazing [105,170]. In Mississippi, mowing seedlings 13 days after emergence killed them [126]. In an Alabama field experiment, multiple cuttings, starting when plants were 1 foot (cm) high, slowed Johnson grass rhizome development. At the end of the growing season, plots cut 8 times averaged 15 dry-weight oz (431 g) of Johnson grass top-growth and 0.3 dry-weight oz (10 g) of rhizomes. Plants cut only twice had 67 oz (1,909 g) top-growth and 26 oz (739 g) of rhizomes. Plots were 4 × 5 feet [180].

Flooding for 3 to 6 weeks in early spring, before rhizomes sprout, can effectively control Johnson grass. Replacing open irrigation ditches with culverts or pipes helps prevent reinfestation [128].

Hand-pulling Johnson grass usually leaves rhizome pieces behind in the soil, stimulating sprouting. It is not an effective control method unless all rhizomes are removed or new sprouts are controlled [105,170]. Best results are obtained in early spring when soil in moist and rhizomes are least likely to break [170].

Repeated solarization treatments (using a clear polyethylene tarp to trap solar heat in the soil) can control small Johnson grass infestations [13].

Seeds: Solarization of moist soil at 140 °F to 150 °F (60-70 °C) for 7 days kills most Johnson grass seeds. Solarization of dry soil does not kill Johnson grass seed [55]. In Davis, California, soil watered and solarized for 9-12 weeks supported no Johnson grass. Untreated control plots showed 58% Johnson grass cover [56]. For established plants, 30 days of solarization kills most Johnson grass. Remaining plants have grown rhizomes through and above the landscape fabric, but rhizomes above the landscape fabric were easily removed by hand-pulling [122].

Sorghum halepense: References

1. Abuereish, G. M.; Lahham, J. N. 1987. Selenium in soils and plants of the Jordan Valley. Journal of Arid Environments. 12(1): 1-7. [46612]

2. Alcoze, Thomas M.; Zimmerman, Earl G. 1973. Food habits and dietary overlap of two heteromyid rodents from the mesquite plains of Texas. Journal of Mammalogy. 54: 900-908. [9887]

3. Allen, James A. 1990. Establishment of bottomland oak plantations on the Yazoo National Wildlife Refuge Complex. Southern Journal of Applied Forestry. 14(4): 206-210. [14615]

4. Anderson, Darwin; Hamilton, Louis P.; Reynolds, Hudson G.; Humphrey, Robert R. 1953. Reseeding desert grassland ranges in southern Arizona. Bulletin 249. Tucson, AZ: University of Arizona, Agricultural Experiment Station. 32 p. [4439]

5. Anderson, L. E. 1961. Johnsongrass in Kansas. Circular 380. Manhattan, KS: Kansas State University of Agriculture and Applied Science, Agricultural Experiment Station. 12 p. [46608]

6. Anderson, L. E.; Appleby, A. P.; Weseloh, J. W. 1960. Characteristics of Johnsongrass rhizomes. Weeds. 8: 402-406. [47296]

7. Andrews, O. N.; Jr.; Billman, R. C.; Timmons, F. D. 1974. Glyphosate control of railroad rights-of-way vegetation in the Southeast. In: Proceedings, 27th annual meeting of the Southern Weed Science Society; 1974 January 22-24; Atlanta, GA. SWSPBE 27 1-477. [Place of publication unknown]: Southern Weed Science Society: 251-258. [46664]

8. Arle, H. F.; Hamilton, K. C.; McRae, G. M. 1958. Johnson grass control with dalapon and liquefied petroleum burners. Bulletin 293. Tucson, AZ: University of Arizona, Agricultural Experiment Station. 13 p. [46857]

9. Arle, H. Fred; Everson, E. H. 1955. Johnson grass control. Bulletin 265. Tucson, AZ: University of Arizona, Agricultural Experiment Station. 9 p. [46704]

10. Arno, Stephen F. 2000. Fire in western forest ecosystems. In: Brown, James K.; Smith, Jane Kapler, eds. Wildland fire in ecosystems: Effects of fire on flora. Gen. Tech. Rep. RMRS-GTR-42-vol. 2. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station: 97-120. [36984]

11. Arriola, Paul E.; Ellstrand, Norman C. 1996. Crop-to-weed gene flow in the genus Sorghum (Poaceae): spontaneous interspecific hybridization between johnsongrass, Sorghum halepense, and crop sorghum, S. bicolor. American Journal of Botany. 83(9): 1153-1160. [27602]

12. Aslam, M.; Whitworth, R. J. 1988. Development of the southwestern corn borer, Diatraea grandiosella Dyar, on corn and johnsongrass. The Southwestern Entomologist. 13(3): 191-197. [46601]

13. Bainbridge, David A. 1990. Soil solarization for restorationists. Restoration & Management Notes. 8(2): 96-98. [14160]

14. Baker, K. G.; Mayton, E. L. 1944. A year-around grazing program for the alkaline soils of the Black Belt of Alabama. Journal of the American Society of Agronomy. 36(9): 740-748. [46627]

15. Barrentine, W. L.; Snipes, C. E.; Smeda, R. J. 1992. Herbicide resistance confirmed in johnsongrass biotypes. In: Research report. Mississippi State, MS: Mississippi State University, Agricultural & Forestry Experiment Station. 17(5): 1-5. [46652]

16. Battaglia, L. L.; Keough, J. R.; Pritchett, D. W. 1995. Early secondary succession in a southeastern U.S. alluvial floodplain. Journal of Vegetation Science. 8(2): 769-776. [28881]

17. Battaglia, Loretta L. 1991. Early secondary succession in a bottomland hardwood area. Monroe, LA: Northeast Louisiana University. 87 p. Thesis. [42469]

18. Battaglia, Loretta L.; Minchin, Peter R.; Pritchett, Davis W. 2002. Sixteen years of old-field succession and reestablishment of a bottomland hardwood forest in the lower Mississippi alluvial valley. Wetlands. 22(1): 1-17. [41833]

19. Bendixen, Leo E. 1988. Johnsongrass (Sorghum halepense) management systems. Weed Technology. 2(1): 64-67. [46711]

20. Bendixen, Leo E.; Lee, Richard D. 1989. Seasonal trends of postemergence herbicide phytotoxicity in Johnsongrass (Sorghum halepense). In: Johnsongrass (Sorghum halepense) physiology and control. Special Circular 125. Wooster, OH: Ohio State University, Agricultural Research and Development Center: 1-7. [46670]

21. Bendixen, Leo E.; Nandihalli, Ujjanagouda B. 1989. Phytotoxicity of glyphosate, SC-0224, and HOE-39866 for Johnsongrass (Sorghum halepense) control. In: Johnsongrass (Sorghum halepense) physiology and control. Special Circular 125. Wooster, OH: Ohio State University, Agricultural Research and Development Center: 8-14. [46672]

22. Benech Arnold, R. C.; Fenner, M.; Edwards, P. J. 1992. Mineral allocation to reproduction in Sorghum bicolor and Sorghum halepense in relation to parental nutrient supply. Oecologia. 92: 138-144. [47830]

23. Benech Arnold, R. L.; Fenner, M.; Edwards, P. J. 1992. Changes in dormancy level in Sorghum halepense seeds induced by water stress during seed development. Functional Ecology. 6(5): 596-605. [46616]

24. Benech Arnold, R. L.; Ghersa, C. M.; Sanchez, R. A.; Garcia Fernandez, A. E. 1988. The role of fluctuating temperatures in the germination and establishment of Sorghum halepense (L.) Pers. Regulation of germination under leaf canopies. Functional Ecology. 2: 311-318. [47525]

25. Benech Arnold, R. L.; Ghersa, C. M.; Sanchez, R. A.; Insausti, P. 1990. A mathematical model to predict Sorghum halepense (L.) Pers. seedling emergence in relation to soil temperature. Weed Research. 30(2): 81-89. [46691]

26. Benech Arnold, R. L.; Ghersa, C. M.; Sanchez, R. A.; Insausti, P. 1990. Temperature effects on dormancy release and germination rate in in Sorghum halepense (L.) Pers. seeds: a quantitative analysis. Weed Research. 30(2): 81-89. [47829]

27. Benvenuti, Stefano; Macchia, Mario; Miele, Sergio. 2001. Quantitative analysis of emergence of seedlings from buried weed seeds with increasing soil depth. Weed Science. 49(4): 528-535. [46661]

28. Bernard, Stephen R.; Brown, Kenneth F. 1977. Distribution of mammals, reptiles, and amphibians by BLM physiographic regions and A.W. Kuchler's associations for the eleven western states. Tech. Note 301. Denver, CO: U.S. Department of the Interior, Bureau of Land Management. 169 p. [434]

29. Bessin, R. T.; Reagan, T. E. 1990. Fecundity of sugarcane borer (Lepidoptera: Pyralidae), as affected by larval development on gramineous host plants. Environmental Entomology. 19(3): 635-639. [46651]

30. Bigirwa, G.; Adipala, E.; Esele, J. P.; Cardwell, K. F. 2000. Reaction of maize, sorghum, and Johnson grass to Peronosclerospora sorghi. International Journal of Pest Management. 46(1): 1-6. [46620]

31. Bishop, Richard A.; Hungerford, Charles R. 1965. Seasonal food selection of Arizona Mearns quail. Journal of Wildlife Management. 29(4): 813-819. [22955]

32. Boyd, J. W. 1998. Johnsongrass control with MON 37500. Proceedings, Southern Weed Science Society. 51: 193-194. Abstract. [46855]

33. Bradley, Kevin W.; Hagood, Edward S., Jr. 2001. Identification of a Johnsongrass (Sorghum halepense) biotype resistant to aryloxphenoxypropionate and cyclohexanedione herbicides in Virginia. Weed Technology. 15(4): 623-627. [46663]

34. Bransby, D. I.; Ward, C. Y.; Rose, P. A.; [and others]. 1989. Biomass production from selected herbaceous species in the southeastern USA. Biomass. 20: 187-197. [10136]

35. Bridges, D. C.; Chandler, J. M. 1989. A population level temperature-dependent model of seedling johnsongrass (Sorghum halepense) flowering. Weed Science. 37: 471-477. [17406]

36. Brooks, Matthew L.; Esque, Todd C. 2002. Alien plants and fire in desert tortoise (Gopherus agassizii) habitat of the Mojave and Colorado deserts. Chelonian Conservation Biology. 4(2): 330-340. [44468]

37. Brown, Davy R.; Houston, James G. 1993. The nutritive value of range grasses in northern Brewster County, Texas. Texas Journal of Agriculture and Natural Resources. 6: 109-116. [46589]

38. Buchholz, Kenneth; Good, Ralph E. 1982. Density, age structure, biomass and net annual aboveground productivity of dwarfed Pinus rigida Moll. from the New Jersey Pine Barren Plains. Bulletin of the Torrey Botanical Club. 109(1): 24-34. [8639]

39. Buhler, Douglas D.; Hoffman, Melinda L. 1999. Andersen's guide to practical methods of propagating weeds and other plants. 2nd ed. Lawrence, KS: Weed Science Society of America. 248 p. [45403]

40. Burrows, George E.; Tyrl, Ronald J.; Rollins, Dale; Thedford, Thomas R.; McMurphy, Willfred; Edwards, Williams C. [n.d.]. Toxic plants of Oklahoma and the Southern Plains. E-868. Stillwater, OK: Oklahoma State University, Cooperative Extension Service. 40 p. [4994]

41. Bussan, Alvin J.; Dyer, William E. 1999. Herbicides and rangeland. In: Sheley, Roger L.; Petroff, Janet K., eds. Biology and management of noxious rangeland weeds. Corvallis, OR: Oregon State University Press: 116-132. [35716]

42. Campbell, Howard; Martin, Donald K.; Ferkovich, Paul E.; Harris, Bruce K. 1973. Effects of hunting and some other environmental factors on scaled quail in New Mexico. Wildlife Monographs No. 34. Bethesda, MD: The Wildlife Society. 49 p. [23082]

43. Cates, J. S.; Spillman, W. J. 1907. A method of eradicating Johnson grass. Farmers' Bulletin No. 279. Washington, DC: U.S. Department of Agriculture. 16 p. [46647]

44. Chandramohan, S.; Charudattan, R.; Sonoda, R. M.; Singh, Megh. 2002. Field evaluation of a fungal pathogen mixture for the control of seven weedy grasses. Weed Science. 50(2): 204-213. [46660]

45. Chen, Linus Y. 2001. Cost savings from properly managing endangered species habitats. Natural Areas Journal. 21(2): 197-203. [40130]

46. Collins, S. L.; Adams, D. E. 1983. Succession in grasslands: thirty-two years of change in a central Oklahoma tallgrass prairie. Vegetatio. 51: 181-190. [2929]

47. Cox, Jerry R.; Morton, Howard L.; Johnsen, Thomas N., Jr.; [and others]. 1982. Vegetation restoration in the Chihuahuan and Sonoran Deserts of North America. Agricultural Reviews and Manuals ARM-W-28. Washington, DC: U.S. Department of Agriculture, Agriculture Research Service. 37 p. [4600]

48. Crawford, Hewlette S.; Kucera, Clair L.; Ehrenreich, John H. 1969. Ozark range and wildlife plants. Agric. Handb. 356. Washington, DC: U.S. Department of Agriculture, Forest Service. 236 p. [18602]

49. Damalas, Christos A.; Eleftherohorinos, Ilias G. 2001. Dicamba and atrazine antagonism on sulfonylurea herbicides used for johnsongrass (Sorghum halepense) control in corn (Zea mays). Weed Technology. 15(1): 62-67. [46656]

50. Diggs, George M., Jr.; Lipscomb, Barney L.; O'Kennon, Robert J. 1999. Illustrated flora of north-central Texas. Sida Botanical Miscellany No. 16. Fort Worth, TX: Botanical Research Institute of Texas. 1626 p. [35698]

51. Dougherty, P. M.; Edwards, M. B.; Fitzgerald, J. A. 1991. Effects of sulfometuron and imazapyr combinations on Johnsongrass for pine establishment on old fields. Georgia Forest Research Paper 84. [Atlanta, GA]: Georgia Forestry Commission, Research Division. 6 p. [46659]

52. Downs, J. P.; Voth, R. D. 1984. Roadside weed control with glyphosate and sulfometuron methyl combinations. Proceedings, Southern Weed Science Society. [37]

53. Duchesne, Luc C.; Hawkes, Brad C. 2000. Fire in northern ecosystems. In: Brown, James K.; Smith, Jane Kapler, eds. Wildland fire in ecosystems: Effects of fire on flora. Gen. Tech. Rep. RMRS-GTR-42-vol. 2. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station: 35-51. [36982]

54. Egley, G. H.; Chandler, J. M. 1978. Germination and viability of weed seeds after 2.5 years in a 50-year buried seed study. Weed Science. 26(3): 230-239. [19609]

55. Egley, Grant H. 1990. High-temperature effects on germination and survival of weed seeds in soil. Weed Science. 38(4/5): 429-435. [46694]

56. Elmore, Clyde L.; Roncoroni, John A.; Giraud, Deborah D. 1993. Perennial weeds respond to control by soil solarization. California Agriculture. 47(1): 19-22. [46604]

57. Engel-Wilson, Ronald W.; Ohmart, Robert D. 1979. Floral and attendant faunal changes on the lower Rio Grande between Fort Quitman, and Presidio, Texas. In: Johnson, R. Roy; McCormick, J. Frank, technical coordinators. Strategies for protection and management of floodplain wetlands and other riparian ecosystems: Proceedings of the symposium; 1978 December 11-13; Callaway Gardens, GA. Gen. Tech. Rep. WO-12. Washington, DC: U.S. Department of Agriculture, Forest Service: 139-147. [4358]

58. Entry, J. A.; Watrud, L. S.; Reeves, M. 1999. Accumulation of 137Cs and 90Sr from contaminated soil by three grass species inoculated with mycorrhizal fungi. Environmental Pollution. 104(3): 449-457. [46587]

59. Entry, James A.; Watrud, Lidia S.; Reeves, Mark. 2001. Influence of organic amendments on the accumulation of 137Cs and 90Sr from contaminated soil by three grass species. Water, Air, and Soil Pollution. 126(3-4): 385-398. [46653]

60. Eyre, F. H., ed. 1980. Forest cover types of the United States and Canada. Washington, DC: Society of American Foresters. 148 p. [905]

61. Ezell, Andrew W.; Portwood, Jeff; Quicke, Harry. 1999. Pre- and postemergent applications of imazaquin for herbaceous weed control in eastern cottonwood plantations: second year results. In: Haywood, James D., ed. Proceedings, 10th biennial southern silvicultural research conference; 1999 February 16-18; Shreveport, LA. Gen. Tech. Rep. SRS-30. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southern Research Station: 73-75. [34406]

62. Felger, Richard S. 1990. Non-native plants of Organ Pipe Cactus National Monument, Arizona. Tech. Rep. No. 31. Tucson, AZ: University of Arizona, School of Renewable Natural Resources, Cooperative National Park Resources Studies Unit. 93 p. [14916]

63. Fraps, G. S.; Frdge, J. F. 1940. The chemical composition of forage grasses of the East Texas timber country. Bulletin No. 582. College Station, TX: Texas Agricultural Experiment Station. 35 p. [34715]

64. Garrison, George A.; Bjugstad, Ardell J.; Duncan, Don A.; Lewis, Mont E.; Smith, Dixie R. 1977. Vegetation and environmental features of forest and range ecosystems. Agric. Handb. 475. Washington, DC: U.S. Department of Agriculture, Forest Service. 68 p. [998]

65. Ghersa, C. M.; Benech Arnold, R. L.; Martinez-Ghersa, M. A. 1992. The role of fluctuating temperatures in germination and establishment of Sorghum halepense. Regulation of germination at increasing depths. Functional Ecology. 6(4): 460-468. [46615]

66. Ghersa, C. M.; Martinez-Ghersa, M. A.; Satorre, E. H.; Van Esso, M. L.; Chichotky, G. 1993. Seed dispersal, distribution and recruitment of seedlings of Sorghum halepense (L.) Pers. Weed Research. 33(1): 79-88. [46689]

67. Ghersa, C. M.; Satorre, E. H.; Van Esso, M. L. 1985. Seasonal patterns of johnsongrass seed production in different agricultural systems. Israel Journal of Botany. 34((1): 24-30. [46603]

68. Ghersa, C. M.; Satorre, E. H.; Van Esso, M. L.; Pataro, A.; Elizagaray, R. 1990. The use of thermal calendar models to improve the efficiency of herbicide applications in Sorghum halepense (L.) Pers. Weed Research. 30(3): 153-160. [46690]

69. Gilstrap, F. E. 1988. Sorghum-corn-johnsongrass and banks grass mite: a model for biological control in field crops. In: Harris, Marvin K.; Rogers, Charlie E., eds. The entomology of indigenous and naturalized systems in agriculture. Boulder, CO: Westview Press: 141-159. [46580]

70. Gilstrap, Frank E.; Brooks, G. W. 1991. Sorghum midge and midge parasitism on johnsongrass. Journal of Economic Entomology. 84(2): 431-435. [46586]

71. Gleason, Henry A.; Cronquist, Arthur. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. 2nd ed. New York: New York Botanical Garden. 910 p. [20329]

72. Grace, James B.; Smith, Melinda D.; Grace, Susan L.; [and others]. 2001. Interactions between fire and invasive plants in temperate grasslands of North America. In: Galley, Krista E. M.; Wilson, Tyrone P., eds. Proceedings of the invasive species workshop: The role of fire in the control and spread of invasive species; Fire conference 2000: the first national congress on fire ecology, prevention, and management; 2000 November 27 - December 1; San Diego, CA. Misc. Publ. No. 11. Tallahassee, FL: Tall Timbers Research Station: 40-65. [40677]

73. Great Plains Flora Association. 1986. Flora of the Great Plains. Lawrence, KS: University Press of Kansas. 1392 p. [1603]

74. Greenfield, Kirk C.; Chamberlain, Michael J.; Burger, L. Wes, Jr.; Kurzejeski, Eric W. 2003. Effects of burning and discing Conservation Reserve Program fields to improve habitat quality for northern bobwhite (Colinus virginianus). The American Midland Naturalist. 149(2): 344-353. [44087]

75. Greenlee, Jason M.; Langenheim, Jean H. 1990. Historic fire regimes and their relation to vegetation patterns in the Monterey Bay area of California. The American Midland Naturalist. 124(2): 239-253. [15144]

76. Grimes, J. C.; Taylor, W. C. 1930. Johnson grass hay versus timothy hay as a feed for horses and mules. Circular 54. Auburn, AL: Alabama Polytechnic Institute, Agricultural Experiment Station. 8 p. [46650]

77. Groninger, John W.; Baer, Sara G.; Babassana, Didier-Arsene; Allen, David H. 2004. Planted green ash (Fraxinus pennsylvanica Marsh.) and herbaceous vegetation responses to initial competition control during the first 3 years of afforestation. Forest Ecology and Management. 189(1-3): 161-170. [46688]

78. Groves, R. H. 1991. The physiology of grassy weeds in tropical agriculture. In: Baker, R. W. G.; Terry, P. J., eds. Tropical grassy weeds. Wallingford, UK: CAB International for CASAFA: 39-51. [46644]

79. Groves, R. H. 1991. Weeds of tropical Australia. In: Baker, F. W. G., ed. Tropical grassy weeds. Wallingford, UK: CAB International: 189-196. [46665]

80. Guyette, Richard; McGinnes, E. A., Jr. 1982. Fire history of an Ozark glade in Missouri. Transactions, Missouri Academy of Science. 16: 85-93. [5170]

81. Hanson, C. L.; Rieck, C. E.; Herron, J. W.; Witt, W. W. 1976. The johnsongrass problem in Kentucky. Agronomy Notes. Lexington, KY: University of Kentucky , College of Agriculture; Cooperative Extension Service. 9(4): 1-8. [46629]

82. Hardin, James W.; Brownie, Cecil F.; Krings, Alexander; Muirhead, Lyn; Niven, E. Scott. 2003. Plants poisonous to livestock and pets in North Carolina, [Online]. Raleigh, NC: North Carolina State University (Producer). Available: http://ceres.cals.ncsu.edu/wetland/poisonousplants/ [2004, May 14]. [47798]

83. Harper, Horace J. 1930. The use of sodium chlorate in the control of Johnson grass. Journal of the American Society of Agronomy. 22(5): 417-422. [46617]

84. Harrington, George; Capel, Stephen. 1978. Effects of a water resource development project on native prairie in the Flint Hills of Kansas. In: Glenn-Lewin, David C.; Landers, Roger Q., Jr., eds. Proceedings, 5th Midwest prairie conference; 1976 August 22-24; Ames, IA. Ames, IA: Iowa State University: 166-168. [3371]

85. Hartzler, Robert G.; Chappell, William E. 1981. Johnsongrass and its control. Blacksburg, VA: Virginia Polytechnic Institute and State University. 3 p. [Script for slide show]. [46717]

86. Hartzler, Robert G.; Gover, Art; Stellingwerf, Joanne. 1991. Factors affecting winter survival of Johnsongrass (Sorghum halepense) rhizomes. Weed Technology. 5(1): 108-110. [46712]

87. Hauser, Ellis W.; Arle, H. Fred. 1958. Johnson grass as a weed. Farmers' Bulletin No. 1537. Washington, DC: U.S. Department of Agriculture. 14 p. [46593]

88. Hawkins, George E.; Smith, L. A.; Kelley, W. B. 1958. A comparison of Starr millet, sweet sudangrass, and johnsongrass as dairy forages. Leaflet 60. Auburn, AL: Alabama Polytechnic Institute, Agricultural Experiment Station. 4 p. [46575]

89. Hawthorne, Vernon M. 1971. Coyote movements in Sagehen Creek Basin, northeastern California. California Fish and Game. 57(3): 154-161. [25126]

90. Heard, H. C. 1917. Johnson grass control. Bulletin 82. Tucson, AZ: University of Arizona, Agricultural Experiment Station: 339-355. [46706]

91. Hendrickson, William H. 1972. Perspective on fire and ecosystems in the United States. In: Fire in the environment: Symposium proceedings; 1972 May 1-5; Denver, CO. FS-276. [Washington, DC]: U.S. Department of Agriculture, Forest Service: 29-33. In cooperation with: Fire Services of Canada, Mexico, and the United States; Members of the Fire Management Study Group; North American Forestry Commission; FAO. [17276]

92. Herselman, M. J.; Hart, S. P.; Sahlu, T.; Coleman, S. W.; Goetsch, A. L. 1999. Heat energy for growing goats and sheep grazing different pastures in the summer. Journal of Animal Science. 77(5): 1258-1265. [46641]

93. Heyerdahl, Emily K.; Berry, Dawn; Agee, James K. 1994. Fire history database of the western United States. Final report. Interagency agreement: U.S. Environmental Protection Agency DW12934530; U.S. Department of Agriculture, Forest Service PNW-93-0300; University of Washington 61-2239. Seattle, WA: U.S. Department of Agriculture, Pacific Northwest Research Station; University of Washington, College of Forest Resources. 28 p. [+ Appendices]. Unpublished report on file with: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory, Missoula, MT. [27979]

94. Hickman, James C., ed. 1993. The Jepson manual: Higher plants of California. Berkeley, CA: University of California Press. 1400 p. [21992]

95. Hillman, F. H. 1916. Distinguishing characters of the seeds of Sudan grass and Johnson grass. Bulletin No. 406. Washington, DC: U.S. Department of Agriculture, Forest Service. 5 p. [46597]

96. Hoagland, Bruce. 2000. The vegetation of Oklahoma: a classification for landscape mapping and conservation planning. The Southwestern Naturalist. 45(4): 385-420. [41226]

97. Holm, LeRoy G.; Plocknett, Donald L.; Pancho, Juan V.; Herberger, James P. 1977. The world's worst weeds: distribution and biology. Honolulu, HI: University Press of Hawaii. 609 p. [20702]

98. Holshouser, David L.; Chandler, James M. 1996. Predicting flowering of rhizome Johnsongrass (Sorghum halepense) populations using a temperature-dependent model. Weed Science. 44(2): 266-272. [46701]

99. Holshouser, David L.; Chandler, James M.; Wu, Hsin-I. 1996. Temperature-dependent model for non-dormant seed germination and rhizome bud break of Johnsongrass (Sorghum halepense). Weed Science. 44(2): 257-265. [46702]

100. Hsiao, A. I.; Huang, W. Z. 1988. Induction of germination of skotodormant seeds of Johnson grass, Sorghum halepense (L.) Pers. Weed Research. 28(3): 163-174. [46859]

101. Huang, W. Z.; Hsiao, A. I. 1987. Factors affecting seed dormancy and germination of Johnsongrass, Sorghum halepense (L.) Pers. Weed Research. 27: 1-12. [46590]

102. Hull, Richard J. 1968. Johnsongrass life cycle--implications for improving cultural control practices. Research Progress Report 330. Lafayette, IN: Purdue University, Agricultural Experiment Station. 5 p. [46600]

103. Hull, Richard J. 1970. Germination control of Johnsongrass rhizome buds. Weed Science. 18: 118-121. [47799]

104. Huston, J. E.; Rector, B. S.; Merrill, L. B.; Engdahl, B. S. 1981. Nutritional value of range plants in the Edwards Plateau region of Texas. Report B-1375. College Station, TX: Texas A&M University System, Texas Agricultural Experiment Station. 16 p. [4565]

105. Hutchison, Max. 1992. Vegetation management guideline: Johnson grass (Sorghum halepense [L.] Pers.). Natural Areas Journal. 12(4): 219-220. [20073]

106. Jacobson, Brent D.; Murray, Don S.; Stone, John F. 1994. Soil-water extraction profiles of cotton (Gossypium hirsutum) and weed species. Weed Technology. 8(2): 190-198. [46713]

107. Jauset, A. M.; Munoz, M. P.; Pons, X. 2000. Karyotype occurrence and host plants of the corn leaf aphid (Homoptera: Aphididae) in a Mediterranean region. Annuals of the Entomological Society of America. 93(5): 1116-1122. [46654]

108. Johnson, Mark K. 1986. Estimating ratios of live and dead plant material in clipped plots. Journal of Range Management. 39(1): 90. [46613]

109. Johnson, William; Jordan, David; Frans, Robert; McClelland, Marilyn. 1990. Johnsongrass control and regrowth with postemergence grass herbicides. Arkansas Farm Research. Fayettville, AR: Arkansas Agricultural Experiment Station. 39(4): 6. [46854]

110. Kartesz, John T.; Meacham, Christopher A. 1999. Synthesis of the North American flora (Windows Version 1.0), [CD-ROM]. Available: North Carolina Botanical Garden. In cooperation with the Nature Conservancy, Natural Resources Conservation Service, and U.S. Fish and Wildlife Service [2001, January 16]. [36715]

111. Kartesz, John Thomas. 1988. A flora of Nevada. Reno, NV: University of Nevada. 1729 p. [In 3 volumes]. Dissertation. [42426]

112. Kearney, Thomas H.; Peebles, Robert H.; Howell, John Thomas; McClintock, Elizabeth. 1960. Arizona flora. 2d ed. Berkeley, CA: University of California Press. 1085 p. [6563]

113. Kempen, Harold M. 1984. Cotton production losses from weed competition in Kern County: a three year evaluation. In: Proceedings, Western Society of Weed Science. 37: 47-51. [25180]

114. Kintzios, S.; Markidis, M.; Passadeos, K.; Economou, G. 1999. In vitro expression of variation of glyphosate tolerance in Sorghum halepense. Weed Research. 39(1): 49-55. [46693]

115. Kittams, Walter H.; Evans, Stanley L.; Cooke, Derrick C. 1979. Food habits of mule deer on foothills of Carlsbad Caverns National Park. In: Genoways, Hugh H.; Baker, Robert J., eds. Biological investigations in the Guadalupe Mountains National Park: Proceedings of a symposium; 1975 April 4-5; Lubbock, TX. Proceedings and Transactions Series No. 4. Washington, DC: U.S. Department of the Interior, National Park Service: 403-426. [16023]

116. Klingman, Glenn C. 1949. Pre-emergence control of Bermuda grass and Johnson grass with 2,4-D. Agronomy Journal. 41(12): 587-589. [46638]

117. Koostra, James B.; Kinucan, Robert J.; Davis, Delmer I. 1992. A comparison of microbial cellulase and live cell rumen inoculum for estimating in vitro digestibility of range grasses. Texas Journal of Agriculture and Natural Resources. 5: 67-71. [34980]

118. Kucera, Clair L. 1981. Grasslands and fire. In: Mooney, H. A.; Bonnicksen, T. M.; Christensen, N. L.; [and others], technical coordinators. Fire regimes and ecosystem properties: Proceedings of the conference; 1978 December 11-15; Honolulu, HI. Gen. Tech. Rep. WO-26. Washington, DC: U.S. Department of Agriculture, Forest Service: 90-111. [4389]

119. Kuchler, A. W. 1964. United States [Potential natural vegetation of the conterminous United States]. Special Publication No. 36. New York: American Geographical Society. 1:3,168,000; colored. [3455]

120. Lee, Richard D.; Bendixen, Leo E. 1989. Gibberellic acid altered Johnsongrass (Sorghum halepense) response to postemergence graminicides. In: Johnsongrass (Sorghum halepense) physiology and control. Special Circular 125. Wooster, OH: Ohio State University, Agricultural Research and Development Center: 22-27. [46674]

121. Looker, D. 1981. Johnsongrass has an Achilles heel. New Farm. 3: 40-47. [47800]

122. Martin, Chris A.; Ponder, Harry G.; Gilliam, Charles H. 1991. Evaluation of landscape fabrics in suppressing growth of weed species. Journal of Environmental Horticulture. 9(1): 38-40. [20292]

123. Martin, William C.; Hutchins, Charles R. 1981. A flora of New Mexico. Volume 2. Germany: J. Cramer. 2589 p. [37175]

124. McCoy, John W.; Keeland, Bobby D.; Lockhart, Brian Roy; Dean, Thomas. 2002. Preplanting site treatments and natural invasion of tree species onto former agricultural fields at the Tensas River National Wildlife Refuge, Louisiana. In: Outcalt, Kenneth W., ed. Proceedings, 11th biennial southern silvicultural research conference; 2001 March 20-22; Knoxville, TN. Gen. Tech. Rep. SRS-48. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southern Research Station: 405-411. [41512]

125. McPherson, Guy R. 1995. The role of fire in the desert grasslands. In: McClaran, Mitchel P.; Van Devender, Thomas R., eds. The desert grassland. Tucson, AZ: The University of Arizona Press: 130-151. [26576]

126. McWhorter, C. G. 1961. Morphology and development of Johnsongrass plants from seeds and rhizomes. Weeds. 9: 558-562. [47297]

127. McWhorter, C. G. 1972. Factors affecting johnsongrass rhizome production and germination. Weed Science. 20(1): 41-45. [17452]

128. McWhorter, C. G. 1981. Johnsongrass...as a weed. Farmers' Bulletin No. 1537. Washington, DC: U.S. Department of Agriculture. 19 p. [46628]

129. McWhorter, Chester G. 1989. History, biology, and control of johnsongrass. Review of Weed Science. 4: 85-121. [46578]

130. McWhorter, Chester G. 1993. A 16-year survey on levels of Johnsongrass (Sorghum halepense) in Arkansas, Louisiana, and Mississippi. Weed Science. 41(4): 669-677. [46696]

131. Millhollon, Rex. 2000. Loose kernel smut for biocontrol of Sorghum halepense in Saccharum sp. hybrids. Weed Science. 48(5): 645-652. [46611]

132. Mitchell, Rob; Dabbert, Brad. 2000. Potential fire effects on seed germination of four herbaceous species. Texas Journal of Agriculture and Natural Research. 13: 99-103. [46648]

133. Mohlenbrock, Robert H. 1986. [Revised edition]. Guide to the vascular flora of Illinois. Carbondale, IL: Southern Illinois University Press. 507 p. [17383]

134. Mueggler, W. F. 1970. Objectionable characteristics of range plants. In: Range and wildlife habitat evaluation--a research symposium: Proceedings; 1968 May; Flagstaff, AZ; Tempe, AZ. Misc. Publ. 1147. Washington, DC: U.S. Department of Agriculture, Forest Service: 63-70. [12986]

135. Myers, Ronald L. 2000. Fire in tropical and subtropical ecosystems. In: Brown, James K.; Smith, Jane Kapler, eds. Wildland fire in ecosystems: Effects of fire on flora. Gen. Tech. Rep. RMRS-GTR-42-vol. 2. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station: 161-173. [36985]

136. Newman, Dara. 1993. Element stewardship abstract: Sorghum halepense, [Online]. In: Invasives on the web: The Nature Conservancy wildland invasive species program. Davis, CA: The Nature Conservancy (Producer). Available: http://tncweeds.ucdavis.edu/esadocs/documnts/sorghal.html [2004, March 24]. [47797]

137. Newton, R. J.; Goodin, J. R. 1985. Unconventional arid land plants as biomass feedstocks for energy. In: Wickens, G. E.; Goodin, J. R.; Field, D. V., eds. Plants for arid lands: Proceedings, Kew international conference on economic plants for arid lands; 1984 July 23-27; Kew, England. London: Allen & Unwin: 385-397. [42360]

138. Obermeier, Michelle R. 1990. Enzymatic, molecular, and genetic characterization of acetyl coenzyme A carboxylase inhibitor resistant and susceptible Johnsongrass (Sorghum halepense) biotypes. Lexington, KY: University of Kentucky. 108 p. Dissertation. [46669]

139. Obrigawitch, T. T.; Kenyon, W. H.; Kuratle, H. 1990. Effect of application timing on rhizome johnsongrass (Sorghum halepense) control with DPX-V9360. Weed Science. 38: 45-49. [17404]

140. Odum, Eugene P.; Park, Tae Yoon; Hutcheson, K. 1994. Comparison of the weedy vegetation in old-fields and crop fields on the same site reveals that fallowing crop fields does not result in seedbank buildup of agricultural weeds. Agriculture Ecosystems & Environment. 49(2): 247-252. [46637]

141. Odum, Eugene P.; Pomeroy, Steven E.; Dickinson, J. C., III; Hutcheson, Kermit. 1974. The effects of late winter litter burn on the composition, productivity and diversity of a 4-year old fallow-field in Georgia. In: Proceedings, annual Tall Timbers fire ecology conference; 1973 March 22-23; Tallahassee, FL. No. 13. Tallahassee, FL: Tall Timbers Research Station: 399-419. [17413]

142. Overpeck, J. C. 1925. Johnson grass eradication. Bulletin No. 146. Las Cruces, NM: New Mexico College of Agriculture and Mechanic Arts, Agricultural Experiment Station. 15 p. [46609]

143. Pammel, L. H.; King, C. M. 1919. Johnson grass as a weed in southwestern Iowa. Circular No. 55. Ames, IA: Iowa State University, Agricultural Experiment Station. 4 p. [46646]

144. Paterson, Andrew H.; Schertz, Keith F.; Lin, Yann-Rong; Liu, Sin-Chieh; Chang, Yueh-Long. 1995. The weediness of wild plants: molecular analysis of genes influencing dispersal and persistence of johnsongrass (Sorghum halepense (L.) Pers. Proceedings, National Academy of Sciences. 92(13): 6127-6131. [46655]

145. Paysen, Timothy E.; Ansley, R. James; Brown, James K.; [and others]. 2000. Fire in western shrubland, woodland, and grassland ecosystems. In: Brown, James K.; Smith, Jane Kapler, eds. Wildland fire in ecosystems: Effects of fire on flora. Gen. Tech. Rep. RMRS-GTR-42-volume 2. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station: 121-159. [36978]

146. Pena-Rodriguez, L. M.; Armingeon, N. A.; Chilton, W. S. 1988. Toxins from weed pathogens, I. Phytotoxins from a Bipolaris pathogen of Johnson grass. Journal of Natural Products. 51(5): 821-828. [46622]

147. Pollock, E. O. 1927. Johnson grass in Texas. Circular No. 43. College Station, TX: Agricultural and Mechanical College of Texas, Agricultural Experiment Station. 15 p. [46705]

148. Prostko, Eric P.; Wu, Hsini-I; Chandler, J. Michael. 1998. Modeling seedling Johnsongrass (Sorghum halepense) emergence as influenced by temperature and burial depth. Weed Science. 46(5): 549-554. [46698]

149. Quinnild, Clayton L.; Cosby, Hugh E. 1958. Relicts of climax vegetation on two mesas in western North Dakota. Ecology. 39(1): 29-32. [1925]

150. Radford, Albert E.; Ahles, Harry E.; Bell, C. Ritchie. 1968. Manual of the vascular flora of the Carolinas. Chapel Hill, NC: The University of North Carolina Press. 1183 p. [7606]

151. Rankins, D. L., Jr.; Bransby, D. I.; Gregory, W. H. 1992. Johnsongrass - weed or feed? Highlights of Agricultural Research. Auburn, AL: Auburn University, Alabama Agricultural Experiment Station. 39(1): 12. [46598]

152. Rapp, Karl E. 1947. Carbohydrate metabolism of Johnson grass. Journal of the American Society of Agronomy. 39(5): 356-362. [46625]

153. Raunkiaer, C. 1934. The life forms of plants and statistical plant geography. Oxford: Clarendon Press. 632 p. [2843]

154. Rea, H. E. 1958. Spot-spraying johnsongrass. Bulletin 902. College Station, TX: Texas A&M University, Agricultural Experiment Station, Agricultural Extension Service. 14 p. [46596]

155. Rehab, Ibrahim F.; Bendixen, Leo E. 1989. Bentazon and acifluorfen reduce Johnsongrass (Sorghum halepense) control by sethoxydim, fluazifop, and quizalofop. In: Johnsongrass (Sorghum halepense) physiology and control. Special Circular 125. Wooster, OH: Ohio State University, Agricultural Research and Development Center: 32-36. [46679]

156. Reitz, Raulino. 1965. Flora ilustrada catarinense: Planejada e editata, Parte 1. Itajai, Brazil: Herbario Barbosa Rodrigues. 1407 p. [47801]

157. Rice, Peter M. 2001. INVADERS Database System, [Online]. Missoula, MT: University of Montana, Division of Biological Sciences (Producer). Available: http://invader.dbs.umt.edu/ [2004, March 25]. [38172]

158. Robson, Sarah. 2003. Agfact A0.9.66: Prussic acid poisoning in livestock, [Online]. Orange, New South Wales: NSW Agriculture (Producer). Available: http://www.agric.nsw.gov.au/reader/an-health/a0966.htm [2004, January 21]. [46666]

159. Rosales-Robles, Enrique; Chandler, James M.; Senseman, Scott A.; Prostko, Eric P. 1999. Influence of growth stage and herbicide rate on postemergence Johnsongrass (Sorghum halepense) control. Weed Technology. 13(3): 525-529. [46710]

160. Rowe, J. S. 1983. Concepts of fire effects on plant individuals and species. In: Wein, Ross W.; MacLean, David A., eds. The role of fire in northern circumpolar ecosystems. SCOPE 18. New York: John Wiley & Sons: 135-154. [2038]

161. Sapsis, David B. 1990. Ecological effects of spring and fall prescribed burning on basin big sagebrush/Idaho fescue--bluebunch wheatgrass communities. Corvallis, OR: Oregon State University. 105 p. Thesis. [16579]

162. Seifers, Dallas L.; Harvey, Tom L.; Martin, T. J.; Jensen, Stanley G. 1998. A partial host range of the high plains virus of corn and wheat. Plant Disease. 82: 875-879. [46621]

163. Sharma, H. C.; Franzmann, B. A. 2001. Host-plant preference and oviposition responses of the sorghum midge, Stenodiplosis sorghicola (Coquillett) (Dipt., Cecidomyiidae) towards wild relatives of sorghum. Journal of Applied Entomology. 125(3): 109-114. [46588]

164. Sheldon, John J.; Causey, Keith. 1974. Use of Japanese honeysuckle by white-tailed deer. Journal of Forestry. 72(5): 286-287. [41747]

165. Sheley, Roger; Manoukian, Mark; Marks, Gerald. 1999. Preventing noxious weed invasion. In: Sheley, Roger L.; Petroff, Janet K., eds. Biology and management of noxious rangeland weeds. Corvallis, OR: Oregon State University Press: 69-72. [35711]

166. Shiflet, Thomas N., ed. 1994. Rangeland cover types of the United States. Denver, CO: Society for Range Management. 152 p. [23362]

167. Sims, Barry D.; Oliver, Lawrence R. 1990. Mutual influences of seedling Johnsongrass (Sorghum halepense), sicklepod (Cassia obtusifolia), and soybean (Glycine max). Weed Science. 38: 139-147. [11809]

168. Singh, J. S.; Yadava, P. S. 1973. Caloric values of plant and insect species of a tropical grassland. Oikos. 24(2): 186-194. [46623]

169. Smeda, Reid J.; Snipes, Charles E.; Barrentine, William L. 1997. Identification of graminicide-resistant Johnsongrass (Sorghum halepense). Weed Science. 45(1): 132-137. [46700]

170. Solecki, Mary Kay. 1997. Controlling invasive plants. In: Packard, Stephen; Mutel, Cornelia F., eds. The tallgrass restoration handbook: For prairies, savannas, and woodlands. Washington, DC: Island Press: 251-278. [43127]

171. Sperry, O. E.; Dollahite, J. W.; Hoffman, G. O.; Camp, B. J. 1964. Texas plants poisonous to livestock. Report B-1028. College Station, TX: Texas A&M University, Texas Agricultural Experiment Station, Texas Agricultural Extension Service. 59 p. [23510]

172. Stanturf, John A.; Portwood, C. Jeffrey. 1999. Economics of afforestation with eastern cottonwood (Populus deltoides) on agricultural land in the lower Mississippi alluvial valley. In: Haywood, James D., ed. Proceedings, 10th biennial southern silvicultural research conference; 1999 February 16-18; Shreveport, LA. Gen. Tech. Rep. SRS-30. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southern Research Station: 66-72. [34405]

173. Steigman, Kenneth L.; Ovenden, Lynn. 1988. Transplanting tallgrass prairie with a sodcutter. In: Davis, Arnold; Stanford, Geoffrey, eds. The prairie: roots of our culture; foundation of our economy: Proceedings, 10th North American prairie conference; 1986 June 22-26; Denton, TX. Dallas, TX: Native Prairie Association of Texas: 09.01: 1-2. [25602]

174. Stephens, H. A. 1980. Poisonous plants of the central United States. Lawrence, KS: The Regents Press of Kansas. 165 p. [3803]

175. Stickney, Peter F. 1989. Seral origin of species originating in northern Rocky Mountain forests. Unpublished draft on file at: U.S. Department of Agriculture, Forest Service, Intermountain Research Station, Fire Sciences Laboratory, Missoula, MT. 10 p. [20090]

176. Stoller, E. W. 1977. Differential cold tolerance of quackgrass and johnsongrass rhizomes. Weed Science. 25(4): 348-351. [17422]

177. Stomberg, Mark R.; Kephart, Paul; Yadon, Vern. 2001. Composition, invasibility, and diversity in coastal California grasslands. Madrono. 48(4): 236-252. [41371]

178. Strausbaugh, P. D.; Core, Earl L. 1977. Flora of West Virginia. 2nd ed. Morgantown, WV: Seneca Books, Inc. 1079 p. [23213]

179. Stromberg, Juliet C.; Chew, Matthew K. 1997. Herbaceous exotics in Arizona's riparian ecosystems. Desert Plants. 13(1): 11-17. [27407]

180. Sturkie, D. G. 1930. The influence of various top-cutting treatments on rootstocks of Johnson grass (Sorghum halepense). Journal of the American Society of Agronomy. 22(1): 82-93. [46618]

181. Talbot, M. W. 1940. Johnson grass as a weed. Farmers' Bulletin No. 1537 (revised). Washington, DC: U.S. Department of Agriculture. 10 p. [46594]

182. Taylorson, R. B.; McWhorter, C. G. 1969. Seed dormancy and germination in ecotypes of Johnsongrass. Weed Science. 17: 359-361. [47295]

183. Tellman, Barbara. 1998. Stowaways and invited guests: how some exotic plant species reached the American Southwest. In: Tellman, Barbara; Finch, Deborah M.; Edminster, Carl; Hamre, Robert, eds. The future of arid grasslands: identifying issues, seeking solutions: Proceedings; 1996 October 9-13; Tucson, AZ. Proceedings RMRS-P-3. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station: 144-149. [29294]

184. Tu, Mandy; Hurd, Callie; Randall, John M., eds. 2001. Weed control methods handbook: tools and techniques for use in natural areas. Davis, CA: The Nature Conservancy. 194 p. [37787]

185. Tutin, T. G.; Heywood, V. H.; Burges, N. A.; [and others]. 1980. Flora Europaea. Vol. 5: Alismataceae to Orchidaceae (Monocotyledones). Cambridge, UK: University Press. 452 p. [36390]

186. U.S. Department of Agriculture, Animal and Plant Health Inspection Service (APHIS), National Plant Board. 2003. Federal and state plant quarantine summaries, [Online]. In: Plant laws and regulations. National Plant Board (Producer). Available: http://www.aphis.usda.gov/npb/F&SQS/sqs.html [2004, March 29]. [47301]

187. U.S. Department of Agriculture, Forest Service, Eastern Region. 2004. Eastern Region invasive plants ranked by degree of invasiveness, [Online]. In: Noxious weeds and non-native invasive plants. Section 3: Invasive plants. Milwaukee, WI: Eastern Region (Producer). Available: http://www.fs.fed.us/r9/wildlife/range/weed/Sec3B.htm [2004, February 16]. [46748]

188. U.S. Department of Agriculture, Forest Service, Southern Region. 2001. Regional invasive exotic plant species list. Regional Forester's list and ranking structure: invasive exotic plant species of management concern, [Online]. In: Invasive plants of southern states list. Southeast Exotic Pest Plant Council (Producer). Available: http://www.se-eppc.org/fslist.cfm [2003, August 25]. [44944]

189. U.S. Department of Agriculture, National Resource Conservation Service. 2004. PLANTS database (2004), [Online]. Available: http://plants.usda.gov/. [34262]

190. Unger, P. W.; Miller, S. D.; Jones, O. R. 1999. Weed seeds in long-term dryland tillage and cropping system plots. Weed Research. 39(3): 213-223. [46692]

191. Van Auken, O. W.; Bush, J. K. 1991. Influence of shade and herbaceous competition on the seedling growth of two woody species. Madrono. 38(3): 149-157. [16572]

192. Vinall, H. N. 1926. Johnson grass: its production for hay and pasturage. Farmers' Bulletin No. 1476. Washington, DC: U.S. Department of Agriculture. 21 p. [46643]

193. Vincent, Dwain W. 1992. The sagebrush/grasslands of the upper Rio Puerco area, New Mexico. Rangelands. 14(5): 268-271. [19698]

194. Vora, Robin S. 1989. Fire in an old field adjacent to a sabal palm grove in south Texas. Texas Journal of Science. 41(1): 107-108. [7063]

195. Voss, Edward G. 1972. Michigan flora. Part I: Gymnosperms and monocots. Bloomfield Hills, MI: Cranbrook Institute of Science; Ann Arbor, MI: University of Michigan Herbarium. 488 p. [11471]

196. Wade, Dale D.; Brock, Brent L.; Brose, Patrick H.; [and others]. 2000. Fire in eastern ecosystems. In: Brown, James K.; Smith, Jane Kapler, eds. Wildland fire in ecosystems: Effects of fire on flora. Gen. Tech. Rep. RMRS-GTR-42-vol. 2. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station: 53-96. [36983]

197. Warwick, S. I.; Black, L. D. 1983. The biology of Canadian weeds. 61. Sorghum halepense (L.) Pers. Canadian Journal of Plant Science. 63: 997-1014. [17451]

198. Warwick, S. I.; Phillips, D.; Andrews, C. 1986. Rhizome depth: the critical factor in winter survival of Sorghum halepense (L.) Pers. (Johnson grass). Weed Research. 26: 381-387. [10037]

199. Warwick, S. I.; Thompson, B. K.; Black, L. D. 1984. Population variation in Sorghum halepense, Johnson grass, at the northern limits of its range. Canadian Journal of Botany. 62(9): 1781-1790. [46639]

200. Washburn, Brian E.; Barnes, Thomas G.; Rhoades, Charles C.; Remington, Rick. 2002. Using imazapic and prescribed fire to enhance native warm-season grasslands in Kentucky, USA. Natural Areas Journal. 22(1): 20-27. [42553]

201. Weber, William A.; Wittmann, Ronald C. 1996. Colorado flora: eastern slope. 2nd ed. Niwot, CO: University Press of Colorado. 524 p. [27572]

202. Welsh, Stanley L.; Atwood, N. Duane; Goodrich, Sherel; Higgins, Larry C., eds. 1987. A Utah flora. The Great Basin Naturalist Memoir No. 9. Provo, UT: Brigham Young University. 894 p. [2944]

203. Wheeler, W. A.; Hill, D. D. 1957. Grassland seeds: a handbook of information about the grass and legume seeds used for forage, pasture, soil conservation, and other turf planting in the United States. Princeton, NJ: D. Van Nostrand Company, Inc. 734 p. [25754]

204. Wiese, A. F.; Sweeten, J. M.; Bean, B. W.; Salisbury, C. D.; Chenault, E. W. 1998. High temperature composting of cattle feedlot manure kills weed seed. Applied Engineering in Agriculture. 14(4): 377-380. [46852]

205. Wiggins, Ira L. 1980. Flora of Baja California. Stanford, CA: Stanford University Press. 1025 p. [21993]

206. Wright, Henry A.; Bailey, Arthur W. 1982. Fire ecology: United States and southern Canada. New York: John Wiley & Sons. 501 p. [2620]

207. Wunderlin, Richard P. 1998. Guide to the vascular plants of Florida. Gainesville, FL: University Press of Florida. 806 p. [28655]

208. Yang, Y. W.; Newton, R. J.; Miller, F. R. 1990. Salinity tolerance in Sorghum. II. Cell culture response to sodium chloride in S. bicolor and S. halepense. Crop Science. 30(4): 781-785. [46624]

209. Yassin, Mohanned A.; Bendixen, Leo E. 1989. Effect of gibberellic acid on postemergence herbicide phytotoxicity in Johnsongrass (Sorghum halepense). In: Johnsongrass (Sorghum halepense) physiology and control. Special Circular 125. Wooster, OH: Ohio State University, Agricultural Research and Development Center: 15-21. [46673]

210. Yim, Kyu-Ock; Bayer, David E. 1997. Rhizome expression in a selected cross in the Sorghum genus. Euphytica. 94(2): 253-256. [46584]

211. Young, James A.; Evans, Raymond A. 1981. Demography and fire history of a western juniper stand. Journal of Range Management. 34(6): 501-505. [2659]

212. Youtie, Berta; Soll, Jonathan. 1990. Diffuse knapweed control on the Tom McCall Preserve and Mayer State Park. Unpublished report (prepared for the Mazama Research Committee) on file at: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory, Missoula, MT. 18 p. [38353]

213. Zahnley, J. W.; Fitch, J. B. 1941. Effect of ensiling on the viability of weed seeds. Journal of the American Society of Agronomy. 33(9): 816-822. [46619]