Medusahead [Taeniatherum caput-medusae (L.) Nevski][ELYCM][CalEPPC: A-1][CDFA list: C] Photographs
SYNONYMS: Elymus caput-medusae L., Hordeum caput-medusae (L.) Crosson & Durand, Cuviera caput-medusae (L.) Simk., Taeniatherum asperum (Simonk.) Nevski, Taeniatherum caput-medusae (L.) Nevski ssp. asperum (Simk.) Melderis, Taeniatherum crinitum (Schreb.) Nevski var. caput-medusae (L.) Wipff, and many others. At publication time the relationships and nomenclature for the taxa in the genus Taeniatherum remain controversial.
GENERAL DESCRIPTION: Noxious winter annual to 0.6 m tall. Medusahead typically invades rangeland communities. Dense stands often develop, displacing desirable vegetation and wildlife, and lowering the livestock carrying capacity. Relative to other forage species, medusahead contains much silica, making it harsh and unpalatable to livestock except during the early growth stages. The stiff awns and hard florets can injure eyes and mouths of grazing animals. Seed-eating birds usually avoid feeding on the seeds. Senesced plants form a dense layer of litter that decomposes slowly, changing the temperature and moisture dynamics of the soil, greatly reducing seed germination of other species, and creating more fuel for wildfires. Medusahead matures 2-4 weeks later in the season than most other annual grasses. The yellowish-green sheen of dense stands is highly visible after other annual grasses turn brown. Introduced from Europe. The western U.S. endemic crown rot fungus (Fusarium culmorum) is a potential biocontrol agent adapted to dry soils.
SEEDLINGS: Remain attached to the long-awned florets. Vegetative characteristics are similar to those of mature plants, except blades are ~ 0.5 mm wide. Seedlings can survive desiccation of the primary root and develop adventitious roots when moisture becomes available.
MATURE PLANT: Stems slender, +/- ascending. Blades ~1-3 mm wide, flat to +/- in-rolled along the margins, typically 2-4 per stem. Leaves and sheath glabrous or covered with minute hairs. Sheath open. Ligules membranous, up to 0.5 mm long, truncate. Collar region usually sparsely long-hairy. Auricles glabrous, up to ~ 0.5 mm long. The surface of mature foliage often appears glassy under magnification.
ROOTS and UNDERGROUND STRUCTURES: Fibrous roots grow throughout the cool season, deplete upper soil moisture early in the season, and access deep soil moisture late in the growing season. Seedling roots grow faster than those of downy brome (Bromus tectorum).
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SPIKELETS/FLORETS: Heads spike-like, 1.5-5 cm long excluding awns, main axis does not break apart in fruit. Spikelets 2 per node. Florets 2 per spikelet, the upper much reduced and sterile. Fertile lemma narrowly lanceolate, ~ 5-8 mm long, 3-veined, tapered into a straight to curved awn ~ 3-7 cm long. Lemma surface covered with minute glassy barbs and papillae (magnification required). Glumes awn-like, +/- ascending, 1-4 cm long, straight to slightly curved, fused at base. Awns and glumes flattened, stiff, with minute upward pointing barbs lining margins. Spikelets separate from the head above glumes. Self-pollinated.
POSTSENESCENCE CHARACTERISTICS: Old spikes consisting of the ascending glumes remain intact for a long period. Some florets can remain attached to spikes long after plants turn brown.
HABITAT: Disturbed sites, grassland, openings in chaparral, oak woodlands, agronomic fields. Grows best on clay soils or where deep soil moisture is available late in the growing season.
DISTRIBUTION: North Coast Ranges, Cascade Range, Klamath Ranges, Sierra Nevada, Central Valley, South Coast Ranges, northern South Coast (Santa Barbara Co.), Channel Islands; to Washington, Idaho, Utah. To ~ 2100 m (7000 ft). Expanding range.
PROPAGATION/PHENOLOGY: Reproduces by seed. Seed production is prolific. Seeds disperse locally with wind and water and to greater distances with soil movement, human activities, and by clinging to the feet and fur of animals. Newly matured seeds require a cool after-ripening period of ~ 3-4 months and contain a germination inhibitor in the awns that must degrade before germination can occur. Germination is typically rapid and occurs under a broad temperature range (optimal 10-15º C). Most seeds germinate in fall after the first rain, but some seeds remain dormant or germinate in winter or spring. Seeds can germinate in dense litter under low moisture conditions and without directly contacting a moist substrate. Nitrogen can stimulate some dormant seeds to germinate. Seedlings emerge from soil depths up to ~ 8 cm (3-4 in).
MANAGEMENT FAVORING/DISCOURAGING SURVIVAL: Depending on timing, intensity, and other factors, controlled burns may reduce or enhance infestations. Slow hot burns initiated when other vegetation has dried and medusahead seeds have not matured (~ 30 % moisture content), can reduce infestations significantly. Discing or plowing before seed-set can greatly reduce stands.
SIMILAR SPECIES: Unlike medusahead, similar appearing Hordeum and Elymus species have 5-veined lemmas and main flower spike axes that typically break apart in fruit. In addition, Hordeum species have 3 florets per spikelet, with the lateral florets much smaller than the central floret.
CONTROL METHODS:
Prevention: This invasive winter annual grass is found throughout rangelands and wildlands of the Western United States. The serious nature of this undesirable plant is easily recognized by its ability to invade and outcompete dense stands of downy brome (cheatgrass, Bromus tectorum) on degraded rangelands. This problem may be compounded in areas where land managers are aggressively working to control other invasive plants. Without restoration efforts combined with weed management, ranchers and land managers alike may unintentionally replace other exotics with the aggressive medusahead. Controlled grazing may be one of the few ways to prevent medusahead establishment. This includes areas where cheatgrass is the dominate forage species for winter and spring grazing. Overgrazing of cheatgrass will likely shift the balance to favor medusahead, which will result in a downward spiral of decreased grazing capacity. Certain soil types have also been shown to favor medusahead establishment. These include heavy clays or soils with well developed subsurface clay horizons. Low lying areas that receive additional moisture by overland flow or subsurface later moisture flow may also favor medusahead.
Mechanical: Where possible, tillage for seedbed preparation will control existing medusahead plants. Tillage may also bury seed and break up deep thatch layers. However, the increased potential for soil erosion, loss of soil moisture, loss of organic matter, and loss of microbiotic crusts may outweigh the immediate benefits of tillage. Careful consideration of these factors should be made before utilizing tillage in rangeland or wildland areas. Mowing is generally nonselective and fails to remove the meristems where new growth originates. Along roadsides, mowing is not recommended afer seed set due to the increased potential for seed dispersal.
Biological: Very little work has focused on utilizing classical biological control for medusahead. Five soil fungi endemic to the Western United States have been examined. However, results from that study demonstrated a general lack of host specificity for medusahead by these fungi. Winter wheat and crested wheatgrass exhibited some degree of susceptibility to all five fungi. Biological control of medusahead does not appear to be a potential management option in the near future.
Chemical: Chemical control options for medusahead are currently very limited. Glyphosate and paraquat are nonselective herbicides but will only provide variable control of medusahead. Their use is extremely limited where other sensitive species occur. Atrazine is a selective herbicide used for annual grass control and has effectively controlled medusahead and cheatgrass with at 1.12 kg ha-1. However, atrazine may injure perennial grass seedlings and a fallow period prior to grass seeding is necessary. This period may be up to twelve months. Atrazine is currently labeled on a very limited basis for use in rangelands in some states but is not labeled in California. Limited chemical control options for medusahead presents a serious potential problem for California rangelands. Current chemical control strategies in rangelands are dominated by broadleaf herbicides. Controlling broadleaf weeds such as yellow starthistle may result in a species shift to medusahead. This has been observed where picloram, a broadleaf herbicide, was used to control western juniper. Once this shift to medusahead has occurred, fewer options will be available for restoration of productive rangeland. Thus, long term sustainable management of rangelands susceptible to medusahead invasion will require integrated approaches involving revegetation efforts that include desirable species which occupy critical niches susceptible to weed invasion.
Fire: The use of fire has given mixed results for medusahead control. Plant community improvements have been achieved by burning cismontaine areas of California. However, burning in the intermountain areas has resulted in continued medusahead dominance. These mixed results are likely due to differences in the soil seedbank, and plant community recovery time following a burn. An understanding of the natural fire cycles and plant community response to fire is critical for success in medusahead management with fire.
Integrated Management: Although revegetation of medusahead infested areas is critical, successful strategies have not been abundant. There are certain inherent difficulties associated with revegetation of infested areas. Medusahead is one of the few grasses which is adapted for survival on vertisols. These contracting and expanding clay lattices are somewhat unstable in areas of erratic precipitation, and perennial grass seedling establishment is extremely difficult. Difficulties in timing of seedling establishment and seedling predation have also been encountered. Researchers in Idaho attained successful medusahead control with atrazine, but failed to get seedling establishment of crested wheatgrass. Further investigations utilizing soil fumigation revealed an unidentified biologic factor was involved in preventing seedling establishment. This factor was not identified, but was speculated to be either an endemic nematode or soil fungus. The use of squirreltail (Sitanion hysterix) has been successful in areas of the intermountain region. This perennial grass is one of the only natives observed to establish in medusahead communities. Bluebunch wheatgrass, (Pseudoroegneria spicata), previously called Agropyron spicatum, has not been able to establish in medusahead communities without first removing the medusahead. Greenhouse and laboratory studies have shown that medusahead can gain a competitive advantage over bluebunch wheatgrass by rapid germination and early establishment at low temperatures. Similarly, both medusahead and cheatgrass can germinate and establish much more rapidly at low temperatures than either crested or bluebunch wheatgrass, by continuous root elongation over the entire winter. These studies are a good indication of the competitive ability medusahead has compared to native perennials. They also suggest that integrated approaches involving medusahead control may be more successful than revegetation alone.