Species Abstracts of Highly Disruptive Exotic Plants
at Pipestone National Monument
Agropyron repens
Park: Pipestone National Monument (PIPE)
Species: Agropyron repens (L.) Beauv. syn. Elytrigia repens (L.) Nevski
Common Name:Quackgrass, couchgrass
Urgency Ranking: Medium
Overall Ranking: 7
Significance of Impact: 64
- A. Current impact: 28
- B. Ability to be a pest: 36
Taxonomic Description:
Quackgrass is a strongly rhizomatous, sod-forming, perennial grass. It has
an erect to decumbent growth form (50-110 cm tall) with glaucous culms. Leaf
blades are flat (8-30 cm long and 2-18 mm wide) and glabrous to pilose. The
ligule is membranous (0.5-0.8 mm long), obtuse, and entire to ciliate. Auricles
are well developed (3 mm long) and claw-like. Sheaths are round, open, and
glabrous to pilose. The inflorescence is a spike (4-26 cm long). The spikelets
are three- to eight-flowered. Glumes are subequal (5-13 mm long) and tapering
to an acute tip that may be awnless or tipped with an awn (3-6 mm long). Lemmas
(6-12 mm long) are awnless, awn-tipped, or with a short awn (5-7 mm long).
Biology/Ecology:
Quackgrass was introduced to North America from the Mediterranean region in
the early 1900s. It now has a circumpolar distribution and is found in every
state, but it is considered to be a problem only in the northern portion of
this country. It is a highly competitive weed and is allelopathic. It can
rapidly reduce the productivity of desirable vegetation in prairie, cropland,
pastureland, rangeland, and lawns. It is commonly found growing on a wide
variety of soils, but it is most abundant in fine, fertile, moist soils. It
has a pH tolerance range of 4.5 to 8.0 and grows vigorously on alkaline soils
and will grow in saline soils. Quackgrass is only slightly shade tolerant,
and vigor decreases when shading exceeds 50%. It can be most commonly found
growing in moist, disturbed sites such as old fields, ditch banks, drainageways,
and wet pastures.
Quackgrass is a cool-season grass. Seeds germinate either in the fall or spring. Tillering will begin after seedlings reach the four- to six-leaf stage, and rhizomes start to be produced at the six- to eight-leaf stage. Rhizomes actively grow in the summer, producing aerial shoots in the fall. During the first season, plants form a clump through extensive tillering and rhizome formation. During the second season of growth, other clumps develop from the rhizomes, and a patch is formed. In subsequent years, various patches will merge to form a continuous or patchy stand. Flowering occurs from May through August. Seed matures from July to September and is disseminated within a month of maturity. Each quackgrass plant has the potential to produce a high number of seeds and is ranked in the 11-1000 seeds per year category. Quackgrass may flower and produce viable seed more than once a season.
Distribution:
Several widespread and dense populations of quackgrass occur at Pipestone
National Monument (PIPE). If combined, the populations would cover an area
of more than 11 but fewer than 50 hectares. These plants are found in mid-successional
sites disturbed in the last 11 to 50 years. Quackgrass has the potential to
retard natural succession in the park by competing for secondary successional
resources. It has a significant visual impact on the vegetation at PIPE.
Control:
Quackgrass is difficult to control, and a limited number of control methods
are available. An important consideration in controlling this species is that
the seeds have the potential to remain viable in the seed bank for up to 10
years, and it can vigorously spread by rhizomes. A further consideration is
that sources for new propagules surround PIPE.
Prior to applying any control method, it is important to determine if enough desirable plants are present to replace the controlled plants. If desired vegetation is scarce or absent control will be of little value. An alternative may be to follow control with seeding of desirable species. Another consideration is that most control methods harm other plants and the resulting disturbances favor reinvasion by quackgrass or other exotic species.
Cultural control methods for quackgrass include prescribed burning and grazing. Prescribed burning is the most realistic in this setting. Cool-season grasses are usually decreased by repeated late spring (May to early June) prescribed burns. The optimal period may be just prior to inflorescence emergence, and early enough to avoid damage to warm-season grasses. Quackgrass is palatable to herbivores and is one of the earlier plants to start growth in the spring. Concentrated early spring (and late fall) grazing may be used to reduce the vigor and abundance of quackgrass.
Mechanical control methods have some potential to reduce plant vigor and numbers, but they may also stimulate rhizome and tiller production. Repeated mowing to a height of 5 cm or less will reduce seed production and may reduce plant vigor. However, quackgrass will retain its capability to accumulate and store root reserves. Timing is important for mowing treatments. It is necessary to mow only when the plants are actively growing in the spring and fall. Mowing should be suspended when desirable plants begin growth. Repeated tillage from early August until the ground freezes is another method of control, however, it is quite destructive and does not give complete control.
Chemical control methods are limited for quackgrass. Many herbicides are not specific to quackgrass or may not be specifically licensed for this use. It is important to read and follow all label directions. Roundup (glyphosate) may be applied with a hand sprayer on actively growing plants. Other herbicides shown to control quackgrass are Arsenal (imazapyr), Bromax (bromacil), Fusilade 2000 (fluazifop-P-butyl), Hyvar (bromacil), Pramitol (pramitol), Princep (simazine), and Velpar (hexazinone).
No information on the biological control or pests of this species was found in the literature.
References:
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