Quackgrass

Images above: Upper left: Quackgrass auricles (Antonio DiTommaso, Cornell University). Upper right: Quackgrass spikes (Randall Prostak, University of Massachusetts). Bottom: Quackgrass, excavated rhizome and tillers (Antonio DiTommaso, Cornell University).

Identification

Other common names:  quitch grass, couch grass, wheat-grass, shelly-grass, knot-grass, scutch-grass, quick grass, twitch grass, witchgrass, devil's-grass, bluejoint, pondgrass, Colorado bluegrass, false wheat, dog grass, seargrass, quickens, wickens, stroil

Family:  grass family, Poaceae

Habit:  Perennial grass, spreading by shallow rhizomes.

Description:  Seedlings are upright, and the long and narrow seed leaf grows vertically.  Leaves of the seedling are rolled in the bud, smooth below and hairy to smooth above, and 3.5-8” (9-20 cm) long by 0.08-0.1” (0.2-0.25 cm) wide.  The ligule is less than 0.02” (0.05 cm) long and membranous, and auricles are small and often inconspicuous.  The sheath is smooth to hairy and the collar is prominently veined and whitish to pale green.  Mature quackgrass is upright, unbranched, and can reach 4 ft (1.2 m) in height.  Leaves are rolled in the bud and a pair of narrow auricles clasp the stem at the base of each leaf blade.  The ligule is translucent, membranous, and less than 0.04” (0.1 cm) long.  The sheath is open at the top, and hairless to hairy.  Often the sheath of the bottom-most leaf is hairy whereas the sheaths of other leaves are nearly hairless.  Leaf blades are 6-16” (15-40 cm) long and 0.12-0.4” (0.3-1 cm) wide.  The root system is composed of spreading rhizomes with pointed tips and fibrous roots at the nodes.  The rhizomes can spread up to 24” (60 cm) horizontally and extend to 8” (20 cm) below the soil surface.  The inflorescence is a 2-8” (5-20 cm) long, flattened, spike with two alternating rows of numerous, 0.4-0.6” (1-1.5 cm) long spikelets.  The spikelets may have 0.07-0.4” (0.2-1 cm) long awns at the tips.  The inflorescence turns from greenish blue to straw-colored as it matures.  Each spikelet produces 4-6 tan, narrow, oblong, 0.04-0.2” (0.1-0.5 cm) long seeds.  As with all grasses, the apparent seed includes a tight, thin outer layer of fruit tissue.

Similar species:  Tall fescue [Schedonorus arundinaceus (Schreb.) Dumort.], ryegrass (Lolium) species and smooth brome (Bromus inermis Leyss.) may all be mistaken for quackgrass.  Tall fescue is a clump forming grass which lacks rhizomes, and has blunted auricles which do not wrap around the stem like those of quackgrass.  Ryegrasses may have similar auricles to quackgrass, but are non-rhizomatous.  Smooth brome develops rhizomes, but it lacks auricles and has closed sheaths.

Management

Quackgrass tends to increase when the crop rotation includes frequent spring cereal grains and legume forage crops.  The former provides little competitive pressure during quackgrass’s prime spring growth period, and the latter provide nitrogen and long periods for undisturbed growth of the rhizomes.  Since control of severe infestations of quackgrass without the use of herbicides largely requires repeated or intensive tillage, preventing build-up of populations is critical for the maintenance of soil health.

The fastest way to rapidly control a severe quackgrass infestation is to thoroughly dry out the rhizomes.  The traditional English method is to plow the soil when it is wet so that it becomes cloddy.  Then stir the clods repeatedly during dry weather so that the whole plow layer becomes thoroughly dry.  A less effective method that does not require such a long fallow begins by tilling the soil with a chisel plow or field cultivator, at the beginning of a dry period.  The aim of the tillage is to loosen the soil around the rhizomes while leaving the rhizome pieces as long as possible.  Then use a spring-tooth harrow to work the rhizomes to the soil surface to dry.  Use the harrow every few days to speed drying of the soil and bring more rhizomes to the surface, so that most dry thoroughly before the next rain.  If the infestation is particularly dense and the field is small, you can remove a substantial percentage of the rhizomes by bringing them to the surface as explained above, and then raking them onto the field margins.  A window of opportunity for this approach is often available in late summer after harvest of a cereal grain (Brandsӕter et al. 2012) or short season vegetable crop.  Beginning tillage immediately after harvest and preventing fall quackgrass growth is more important than repeated cultivations later in fall (Ringselle et al. 2016).  

The principle approach for managing moderate quackgrass populations involves regular depletion of storage reserves in the rhizomes.  Rhizome reserves are at a minimum when the shoot has developed three leaves (Håkansson and Wallgren 1976), so try to target tillage and cultivation at that growth stage, but disturbance whenever the shoot is showing is useful.  The first tillage of the year should be aimed at cutting the rhizomes into the smallest pieces possible.  Thus, beginning with rotary tillage or disking is more effective than moldboard or chisel plowing.  Following this initial tillage with moldboard plowing, however, is often useful for placing the small rhizome pieces deep in the soil.  They will then have to use up substantial reserves to reach the surface.  Buds on quackgrass rhizomes will sprout at any time during the growing season (Brandsӕter et al. 2010, Tørresen et al. 2010), so many opportunities to deplete reserves occur before and after a summer crop.  For example, before soybeans or a summer vegetable crop, till the soil when quackgrass begins to grow and then delay a few weeks before preparing a seedbed.  Unlike a re-worked seedbed for depleting a surface weed seed bank, however, tillage for seedbed preparation should work the top 6" (15 cm) to disturb as many rhizome fragments as possible.  If necessary, this procedure can be repeated in the fall after harvest, followed by winter grain as a cash or cover crop.  A dense, vigorous stand of winter grain like wheat will competitively suppress quackgrass (Bergkvist et al. 2010).  When row crops are in the ground, continue to cultivate as long as you can get between the rows safely.  The more times the quackgrass shoots are cut off at about the three-leaf stage, the more you will weaken the rhizomes. 

Obviously, the intensive tillage discussed above will tend to deplete soil organic matter and pose a potential erosion risk.  Consequently, they should be used only when quackgrass has become a severe problem or appears likely to become so.  Moreover, when using these practices, you should compensate for the reduced soil organic matter by incorporating cover crops into the crop rotation.  Also, proper equipment can reduce the impact of quackgrass control practices on soil health.  For example, a field cultivator equipped with broad, shallow sweeps can be run shallowly after crop harvest to cut off quackgrass shoots while maintaining crop residue on the soil surface.  When cultivating row crops, shallow low-pitch blades will sever the quackgrass shoots with less oxidation of soil organic matter and disturbance of crop roots, than more conventional sweeps and shovels.

Additional approaches for controlling quackgrass that do not include tillage and are not destructive of soil quality include mowing and interseeded cover crops.  Repeated post-harvest mowing reduced rhizome production and increased grain yield in the subsequent year (Ringselle et al. 2015).  Under-sown cover crops also have the potential to control quackgrass if they can attain growth of at least 900 lb/acre (1000 kg/ha) (Ringselle et al. 2015).  Interseeding red fescue with a winter wheat cash crop at planting will suppress quackgrass (Bergkvist et al. 2010), but red clover can actually benefit rhizome production (Ringselle et al. 2015). 

Quackgrass density usually increases in hay and pasture.  Although quackgrass is nutritious and causes negligible economic loss in the hay crop, you will likely have increased quackgrass when rotating back to annual crops.  Consequently, try to get the quackgrass well under control before sowing the forage.

Ecology

Origin and distribution:  Quackgrass is native to Europe, but it has spread throughout the temperate regions of the world, including North and South America, Asia and Australia (Werner and Rioux 1977).  It is found throughout the United States (including parts of Alaska) and in all Canadian provinces (USDA Plants), but is primarily a problem weed in the northern states.  It is uncommon in dry regions.

Seed weight:  2 mg.

Dormancy and germination:  Newly shed quackgrass seeds are not dormant and require no after-ripening (Werner and Rioux 1977).  They germinate best when exposed to day/night temperature fluctuations of 77/59 °F (25/15 °C) (Werner and Rioux 1977).  Few seeds will germinate at any constant temperature from 41 to 86 °F (5 to 30 °C) (Palmer and Sagar 1963).

Rhizome buds can become dormant in late spring and early summer, but this condition can be broken by nitrate or when severed from the parent plant (Leakey et al. 1977, Werner and Rioux 1977).

Seed/bud longevity:  A few seeds may remain viable in undisturbed soil for 10 years or more, but in normal field conditions few will survive longer than 3 years (Raleigh et al. 1962).  In Alaska, undisturbed seeds declined by 59% per year (Conn et al. 2006). 

Rhizome bud viability declines rapidly in the first year, but it takes two years for all to die (Lemieux et al. 1993).

Season of emergence:  Seedlings emerge in spring into summer (Chepil 1946), but these are uncommon. 

In undisturbed sod, shoots emerge from old rhizomes in early spring (Majek et al. 1984, Palmer and Sagar 1963), whereas shoots arising from the tips of new rhizomes emerge in late summer and fall (Majek et al. 1984, Werner and Rioux 1977).  If the rhizomes are broken by tillage or hoeing, however, new above-ground shoots will arise from the terminal bud of rhizome fragments within a few days regardless of the season.  However, in Sweden, shoot development from exhumed rhizomes declined in fall in response to shortening daylength, but increased again in late fall to spring after exposure to freezing temperatures (Broström et al. 2013).

Emergence depth:  Peak seedling emergence occurs from the top 0.5” (1.3 cm) of the soil, but an occasional seedling may come up from as deep as 4” (10 cm) (Raleigh et al. 1962). 

Shoots can arise from rhizomes at 10” (25 cm) or deeper, though few rhizomes occur naturally at such depths.  In general, shoots from smaller rhizome segments emerged in highest proportions from 1 to 2” (2.5 to 5 cm), whereas shoots from larger segments emerged from depths to 6” (15 cm) (Raleigh et al. 1962). 

Photosynthetic pathway:  C3

Sensitivity to frost:  Quackgrass is highly frost tolerant, and green leaves commonly survive the winter in the northern U.S.A. (Palmer and Sagar 1963).  Rhizome bud populations can increase at temperatures above 32 °F (0 °C), so control late into fall is advised (Lemieux et al. 1993). Quackgrass rhizomes are killed by freezing at temperatures below 20 °F (-6 °C).  Since soil and snow are both good insulators, the rhizomes generally need to be on the soil surface during cold, snow-free weather to freeze.

Drought tolerance:  The species is moderately drought tolerant (Palmer and Sagar 1963).  Rhizomes can regenerate after up to 60% desiccation (Reidy and Swanton 1994).  Therefore, to kill rhizomes, they need to be left on the soil surface during hot, dry weather to thoroughly dry.

Mycorrhiza:  Mycorrhiza were reported as present on quackgrass (Harley and Harley 1987), but it was classified as a weak host in one experiment (Vatovec et al. 2005) and absent in oldfield populations (Dhillion and Friese 1994).

Response to fertility:  Quackgrass is highly responsive to fertilization with N but responds little to P or K (Bandeen and Buchholz 1967, Raleigh et al. 1962).  It is a luxury consumer of nutrients (Werner and Rioux 1977).  It can persist in low fertility soils but is not vigorous under such conditions.

Soil physical requirements:  Quackgrass does well on a variety of soil textures from coarse sands to heavy clays, and on drainage classes from well to poorly drained.  It is also tolerant of salt.  (Werner and Rioux 1977)

Response to shade:  Quackgrass is slightly shade tolerant.  It will persist (without vigor) in meadows of taller vegetation like goldenrod, but is absent from forests.  A reduction in level of light produces an increase in the percentage of rhizome buds developing as shoots (Werner and Rioux 1977).  Only when light is reduced by 97% does rhizome formation cease (Palmer and Sagar 1963).

Sensitivity to disturbance:  The rhizomes are mostly distributed in the top 4” (10 cm) of an untilled sod (Lemieux et al. 1993) where they tend to be cut up during tillage or spading.  This tillage increases the number of shoots but decreases the vigor of each shoot.  New rhizome growth begins in June, so tillage must begin before plants in a sod reach the 6-leaf stage in May or tillage will spread new rhizomes throughout the soil (Majek et al. 1984). 

Time from emergence to reproduction:  Shoots begin growing vigorously in early spring and flower from June through August (Majek et al. 1984).  Long 16-hour days promote formation of elongated stems and inflorescences, but as day length shortens to 12 hours or less, plants shorten and stop producing inflorescences (Majek et al. 1984).  New rhizomes develop when plants have 3-4 leaves if they develop from established rhizomes, but at 6-8 leaves when they develop from seedlings (Werner and Rioux 1977).

Pollination:  The species is wind pollinated and self-sterile (Palmer and Sagar 1963, Werner and Rioux 1977).

Reproduction:  Quackgrass reproduces both vegetatively and by seeds. It typically produces 25-40 seeds per stem (Werner and Rioux 1977).  However, seedlings are rarely observed, probably because many seeds are sterile.  The species requires cross-pollination, and many populations apparently consist of just one to a few clones making effective pollination difficult.  Seed production serves mainly to disperse the species between sites rather than to maintain the population at a particular site.  Most reproduction in a given field or garden is vegetative, with shoots arising from the tips of each rhizome branch (Palmer and Sagar 1963). 

Rhizomes can spread up to 10 ft per year (3 m per year) from the parent plant.  A single rhizome node planted in late fall in Pennsylvania produced 14 rhizomes with a total length of 458 ft (140 m) by the following fall (Raleigh et al. 1962).  If tillage or deep hoeing breaks rhizomes, most segments will produce an above-ground shoot (Palmer and Sagar 1963).  These shoots become independent of the rhizome fragment at the 5 leaf stage, and begin producing new rhizomes at the 3-4 leaf stage (Werner and Rioux 1977).  In heavily infested fields, rhizomes can weigh as much as 7-9 tons/A (16-20 Mg/ha) (Palmer and Sagar 1963).  Production of new rhizomes is favored by a moderate temperature of 70 °F (21 °C) with long day length typical of May or June conditions.  In contrast, production of rhizomes that grow upward to establish new shoots is favored by either a low temperature of 50 °F (10 °C) such as occurs in April or November or by a high temperature of 90 °F (32 °C), as occurs during mid-summer (Majek et al. 1984).

Dispersal:  Seeds are dispersed in hay used for mulch, in manure, and as a contaminant of grain seed (e.g., used for cover crops). 

The rhizomes are commonly dispersed on tillage machinery.  Rhizomes can invade gardens from adjacent weedy areas and species-diverse lawns.  Rhizomes are also sometimes dispersed in the soil surrounding the roots of nursery stock.

Common natural enemies:  Agropyron mosaic virus causes yellow streaking of younger leaves, but does little to reduce the vigor of the plant (Werner and Rioux 1977).  Cattle, sheep and horses find quackgrass desirable forage.  Pigs will grub out the rhizomes and eat them.

Palatability:  Quackgrass is a good forage species with comparable nutritive value, fiber, digestibility, and palatability as other perennial forage grasses (Marten et al. 1987).

Note:  Quackgrass has demonstrated allelopathic effects, which may partly explain the competitiveness of this species (Palmer and Sagar 1963, Raleigh et al. 1962, Werner and Rioux 1977). 

References:

• Bandeen, J. D., and K. P. Buchholtz.  1967.  Competitive effects of quack grass upon corn as modified by fertilization.  Weeds 15:220-224.
• Bergkvist, G., A. Adler, M. Hansson, and M. Weih.  2010.  Red fescue undersown in winter wheat suppresses Elytrigia repens.  Weed Research 50:447-455.
• Brandsӕter, L. O., H. Fogelfors, H. Fykse, E. Graglia, R. K. Hensen, B. Melander, J. Salonen, and P. Vanhala.  2010.  Seasonal restrictions of bud growth on roots of Cirsium arvense and Sonchus arvensis and rhizomes of Elymus repens.  Weed Research 50:102-109.
• Brandsӕter, L. O., M. Goul Thomsen, K. Wӕrnhus, and H. Fykse.  2012.  Effects of repeated clover undersowing in spring cereals and stubble treatments in autumn on Elymus repens, Sonchus arvensis and Cirsium arvense.  Crop Protection 32:104-110.
• Broström, U., L. Andersson, J. Forkman, I. Hakman, J. Liew, and E. Magnuski.  2013.  Seasonal variation in sprouting capacity from intact rhizome systems of three perennial weeds.  Weed Research 53:387-398.
• Chepil, W. S.  1946.  Germination of weed seeds I. Longevity, period of germination, and vitality of seeds in cultivated soil.  Scientific Agriculture 26:307-346.
• Conn, J.S., K.L. Beattie, and A. Blanchard.  2006.  Seed viability and dormancy of 17 weed species after 19.7 years of burial in Alaska.  Weed Science 54: 464-470.
• Dhillion, S. S., and C. F. Friese.  1994.  The occurrence of mycorrhizas in prairies: Applications to ecological restoration.  Thirteenth North American Prairie Conference 13:103-114.
• Håkansson, S., and B. Wallgren. 1976.  Agropyron repens (L.) Beauv., Holcus mollis L. and Agrostis gigantean Roth as weeds—some properties.  Swedish Journal of Agricultural Research 6:109-120.
• Harley, J. L., and E. L. Harley.  1987.  A check-list of mycorrhiza in British flora.  New Phytologist 105:1-102.
• Leakey, R.R.B., R. J. Chancellor, and D. Vince-Prue.  1977.  Regeneration from rhizome fragments of Agropyron repens II. The breaking of 'late spring dormancy' and the influence of chilling and node position on growth from single-node fragments.  Annuls of Applied Biology 87:433-441.
• Lemieux, C., D. Cloutier, and G. D. Leroux.  1993.  Distribution and survival of quackgrass (Elytrigia repens) rhizome buds.  Weed Science 41:600-606.
• Majek, B. A., C. Erickson, and W. B. Duke.  1984.  Tillage effects and environmental influences on quackgrass (Agropyron repens) rhizome growth.  Weed Science 32:376-381.
• Marten, G. C., C. C. Sheaffer, and D. L. Wyse.  1987.  Forage nutritive value and palatability of perennial weeds.  Agronomy Journal 79:980-986.
• Palmer, J. H., and G. R. Sagar.  1963.  Agropyron repens (L.) Beauv. (Triticum repens L.; Elytrigia repens (L.) Nevski).  Journal of Ecology 51:783-794.
• Raleigh, S. M., T. R. Flanagan, and C. Veatoh.  1962.  Life History Studies as Related to Weed Control in the Northeast. 4. Quackgrass.  Northeast Regional Publication.  Bulletin 365.  University of Rhode Island Agricultural Experiment Station, Kingston.
• Reidy, M. E., and C. J. Swanton.  1994.  Response of four quackgrass (Elyrigia repens (L.) Nevski) biotypes to desiccation.  Canadian Journal of Plant Science 74:643-646.
• Ringselle, B., G. Bergkvist, H. Aronsson, and L. Andersson.  2015.  Under-sown cover crops and post-harvest mowing as measures to control Elymus repens.  Weed Research 55, 309–319.
• Ringselle, B., G. Bergkvist, H. Aronsson, and L. Andersson.  2016.  Importance of timing and repetition of stubble cultivation for post-harvest control of Elymus repens.  Weed Research 56:41-49.
• Tørresen, K. S., H. Fykse, and T. Rafoss.  2010.  Autumn growth of Elytrigia repens, Cirsium arvense and Sonchus arvensis at high latitudes in and outdoor pot experiment.  Weed Research 50:353-363.
• USDA Plants.  USDA, Natural Resources Conservation Service.  http://plants.usda.gov
• Vatovec, C., N. Jordan, and S. Huerd.  2005.  Responsiveness of certain agronomic weed species to arbuscular mycorrhizal fungi.  Renewable Agriculture and Food Systems 20:181-189.
• Werner, P. A. and R. Rioux.  1977.  The biology of Canadian weeds. 24. Agropyron repens (L.)  Beauv.  Canadian Journal of Plant Science 57:905-919.