Barnyardgrass

Images above: Upper left: Barnyardgrass seedling (Joseph Neal, North Carolina State University). Upper right: Barnyardgrass inflorescence (Joseph DiTomaso, University of California, Davis). Bottom: Barnyardgrass plant (Randall Prostak, University of Massachusetts).

Identification

Other common names:  water grass, panic-grass, cockspur-grass, cocksfoot panicum, barn-grass, summergrass, billion dollar grass, Japanese millet

Family:  grass family, Poaceae

Habit:  Tall, upright, summer annual grass.

Genus variability:  The genus Echinochloa is composed of many distinct species and ecotype that are difficult to classify. Two distinct clusters of weedy Echinochloa can be distinguished by molecular and morphological markers, namely barnyardgrass (E. crus-galli) and late watergrass [E. oryzicola (Vasinger) Vasinger] (Lee et al. 2016). Both are found in North America, the former is a widespread weed found in many upland habitats whereas the latter, along with early watergrass [E. crus-galli var. oryzoides], are rice mimics that are found in permanently flooded rice fields in California (Godar and Norsworthy 2023). The watergrass species have larger seeds, less seed dormancy, shorter longevity in the soil and greater ability to emerge in deeply flooded fields (Barrett and Wilson 1981, 1983). Junglerice [E. colona (L.) Link] is an important Echinochloa species in rice and other crops in Arkansas, but requires several vegetative, reproductive and seed traits to distinguish from barnyardgrass (Tahir 2016). The discussion below pertains to E. crus-galli unless otherwise noted.

Description:  The first leaf of the seedling is longer (2.5-5.5”) (6.4-14 cm) and more upright than most weedy annual grasses, but shorter and more parallel to the soil surface than later leaves.  All other leaves are vertical and rolled in the bud; thus, they uncurl as they come out of the stem to form a flat or slightly V-shaped surface.  No ligules or auricles are present.  Leaf blades are hairless and rough on the edges.  Seedlings often feel “flat” when held.  The stem may be reddish near the base.  Mature plants have many tillers and grow in clumps.  Plants can reach 5 ft (1.5 m) in height.  Near the base, stems may have a few hairs or may be red-purple in color.  Sheaths are split open near the top so that the underlying sheath of the next leaf is visible. The collar region is white, wide, hairless, with no ligule or auricle.  Leaf blades are 4-8” (10-20 cm) long by 0.12-0.75” (0.3-1.9 cm) wide and have a prominent midvein.  Barnyardgrass has a fibrous root system and can grow new roots where tillers touch the ground.  The inflorescence is a green to purple, lumpy panicle.  Short stalks are widely spaced along the rachis, although this feature can vary.  Seeds are teardrop shaped, brown-gray, and flat on one side, measuring about 0.13” (0.33 cm) in size.  As with other grasses, the apparent seed includes a thin tightly adhering layer of fruit tissue. Seeds have ridges along their length and the attached chaff has awns of 0.13-0.52” (0.33-1.3 cm).

Similar Species:  Aside from the similar Echinochloa species discussed above, similar species occur in other genera.  Fall panicum (Panicum dichotomiflorum Michx.) can be confused with barnyardgrass, but fall panicum has a ligule and coarser foliage than barnyardgrass.  Yellow foxtail [Setaria pumila (Poir.) Roem. & Schult.] has a similar growth habit and red stem bases, but it has a hairy ligule and a somewhat soft inflorescence that resembles a bottlebrush or a fox’s tail.

Management

Since the seeds are only moderately persistent, rotation with perennial forage crops can help reduce density of barnyardgrass. Because barnyardgrass germinates in warm soil, winter grains or grain crops planted in early spring will be highly competitive by the time the weed emerges, and also, shade by the crop will cool the soil and reduce further germination. For summer planted crops, a lag of 2 weeks or more between tillage and seedbed preparation will destroy many seedlings provided the soil is warm and moist. For crops planted in late spring and summer, cultivate frequently and close to the row to control this fast growing weed. Although timely tine weeding or rotary hoeing can greatly reduce the population, some individuals in the row will emerge from deeper than these implements can safely reach. Barnyardgrass may re-emerge following shallow burial, but not if completely buried by 1.6”(4 cm) or more of soil (Mohler et al. 2016). Therefore, hill up soil in the crop row to the fullest extent that the crop will tolerate. Organic mulch placed early will keep the soil cool and suppress germination, but some barnyardgrass may emerge anyway. Mulch placed after the soil warms must be exceptionally dense or thick to be effective. Dense planting of summer cover crops or crops that will tolerate high density helps control this shade intolerant weed. Rice cultivars with tall stature early in the season and many tillers by mid-season tend to be most suppressive of barnyardgrass (Gealy et al. 2019).

Removal of escapes before plants set seeds is useful for long term control in intensively managed vegetable systems. Promptly cleaning up fields after harvest of small grains and vegetables is similarly helpful. In a pair of experiments in Arkansas, 41% of barnyardgrass seeds were still on the plant at soybean harvest, indicating that a significant proportion of seeds could be captured or destroyed during combine harvesting (Schwartz-Lazaro et al. 2017). Subsequent research, however, has demonstrated seed retention of this species to be highly variable (Schwartz-Lazaro et al. 2021).Seed germination was reduced by 50% when the maximum soil temperature reached144 to 154 °F (62 to 68 °C)and by 90% at 169 to 187 °F (76 to 86 °C) (Bitarafan et al. 2022). Solarization with clear plastic for 40 days killed barnyardgrass seeds in the top 1.2”(3cm) of soil, and reduced seed density deeper in the soil (Standifer et al. 1984). Alternately, all barnyardgrass seeds are completely destroyed by narrow-windrow burning of soybean residue (Norsworthy et al. 2020). Electrocution with a Weed ZapperTM controlled the majority of plants in reproductive growth stages, but control of plants at vegetative growth stages was diminished (Schreier et al.2022)

Ecology

Origin and distribution: Barnyardgrass is native to Eurasia (Godar and Norsworthy 2023) and ranges around the world from 50° N to 40° S latitude, except for tropical Africa (Holm et al. 1977).  In North America, it occurs from southern Canada to Mexico (Godar and Norsworthy 2023).  

Seed weight:  Mean seed weight of ten populations varied from 1.7-2.1 mg with most near the lower end of the range (Maun and Barrett 1986), five populations had seed weights ranging from 1.0 to 2.6 mg (Bitarafan et al. 2022), 2.5 mg (Mohler et al. 2016).  Early and late watergrass tend to have higher seed weights (3-4 mg) compared with barnyardgrass (<3 mg) (Godar and Norsworthy 2023).

Dormancy and germination:  Seeds are dormant when shed from the parent plant.  Three to eight months of either dry or moist after-ripening will break dormancy (Rahn et al. 1968, Honek et al. 1999).  Barnyardgrass seeds undergo an innate annual dormancy cycle that is not induced by soil conditions, with germinability reaching a peak in May-July and falling to near zero germinability in September-November (Horng and Leu 1978, Honek et al. 1999).  If the seeds are moist, alternate freezing and thawing for 4 days breaks dormancy of over 65% of seeds.  Two weeks at 40 °F (4 °C) or soaking for four days will each break dormancy of over 30% of seeds (Rahn et al. 1968).  Seed populations from colder highland regions remained dormant through winter months while populations from warmer lowland areas attained various degrees of after-ripening (Martinková et al. 2021).

Seeds of barnyardgrass will germinate at 61-100 °F (16-38 °C), with the optimum temperature for germination varying among populations in the range 77-100 °F (25-38 °C) (Rahn et al. 1968, Martinkova et al. 2006, Guillemin et al. 2013).  Exposure to small amounts of light promotes germination of some seeds, especially after burial over the winter (Taylorson 1970, Taylorson and Dinola 1989), but several days of exposure may be required for full effect (Rahn et al. 1968).  Temperature of 115 °F (46 °C) for as little as 0.5 hr removes the light requirement of most seeds (Taylorson and Dinola 1989).  Nitrate only induces a small increase in percentage germination (Rahn et al. 1968).  Unlike most agricultural weeds, barnyardgrass will germinate when fully immersed in water (Kennedy et al. 1980), however, less so than early and late watergrass which germinate more readily in submersed soils (Godar and Norsworthy 2023).

Seed longevity:  Barnyardgrass seeds can retain high viability for at least 3 years when buried in the soil (Rahn et al. 1968) and a few seeds can persist for up to 13 years (Dawson and Bruns 1975).  One study, however, found less than 6% of seeds survived for six months (Egley and Chandler 1978) and another found approximately 37-42% mortality after one year, but extreme variation in subsequent seed survival among replicates (Dawson and Bruns 1975).  Thus, local conditions can have a large effect on seed survival of barnyardgrass.  Most seeds near the soil surface that do not emerge will lose viability within one year (Taylorson 1970, Dawson and Bruns 1975). 

Season of emergence:  Barnyardgrass begins emerging in mid-spring, reaches peak emergence in late spring or early summer and a few plants continue to emerge until late summer or early fall (Rahn et al. 1968, Holm et al. 1977, Doll 2002, Bagavathiannan et al. 2011).  In California, barnyardgrass emergence is more closely associated with irrigation than with season (Robert Norris, personal communication).

Emergence depth:  Seedlings emerge best from the top 1” (2.5 cm), but substantial emergence occurs from 1-2” (2.5-5 cm).  Seedlings rarely emerge from deeper than 3” (7.5 cm) (Dawson and Bruns 1962, Roché and Muzik 1964, Wiese and Davis 1967, Rahn et al. 1968, Benvenuti et al. 2001).  One report indicates poor emergence from seeds on the soil surface and best emergence begins from the 0.5” (1.3 cm) depth (Rahn et al. 1968).  In flooded conditions, emergence is from the top 0.8” (2 cm) (Holm et al. 1977).

Photosynthetic pathway:  C4 (Elmore and Paul 1983).

Sensitivity to frost:  The species is frost sensitive (Dawson and Bruns 1962).

Drought tolerance:  Growth of young barnyardgrass is reduced more by dry soil than many other weed species and is about as drought tolerant as corn (Wiese and Vandiver 1970).  Roots of well-developed plants reach to more than 40” (1 m) soil depths (Rahn et al. 1968), which allows them to tap deep soil moisture during dry periods.

Mycorrhiza:  Barnyardgrass is mycorrhizal (Harley and Harley 1987).

Response to fertility:  Barnyardgrass is highly responsive to nitrogen fertility, with plant size increasing rapidly with application rates up to 143 lb N/A (160 kg N/ha) (Blackshaw et al. 2003).  Its growth response to increasing P is relatively flat compared to other weeds and crops, but it continues to increase in size with application rates up to 122 lb P2O5/A (137 kg P2O5/ha) (Blackshaw et al. 2004).  It can take up and concentrate phosphorus at the expense of crops (Vengris et al. 1953, Blackshaw et al. 2003).   In Arkansas field margins, it occurred most frequently in soils of pH 6.4-6.8 (Korres et al. 2017).

Soil physical requirements:  Barnyardgrass does best on soils that hold water, but can tolerate soil textures as coarse as loamy sands.  The species is highly tolerant of water logged and flooded soils, and is one of the worst weeds of rice paddies (Maun and Barrett 1968, Holm et al. 1977).  Soils with relatively high water-holding capacity and high fertility provide an ideal substrate for this species (Korres et al. 2017).  It is moderately tolerant of salinity, and suffers less than rice in saline conditions (Chauhan et al. 2013).

Response to shade:  Barnyardgrass tolerates 50% shade well.  Plant weight, but not height is strongly reduced by shade of 73% or more (Rahn et al. 1968).

Sensitivity to disturbance:  Some seedlings will re-emerge following complete burial, provided the soil remains moist (Mohler et al. 2016).  The fibrous root system of medium to large plants makes them difficult to fully uproot with hoes or cultivators.  Barnyardgrass re-grows readily after clipping (Vengris et al. 1966a). 

Time from emergence to maturation:  Plants take longer to mature and produce more seeds when they emerge in spring when day length is increasing, but mature sooner and produce fewer seeds when they emerge in summer when day-length is decreasing (Vengris et al. 1966b, Barrett and Wilson 1981, Keeley and Thullen 1989, Swanton et al. 2000).  Also, plants grow most rapidly at temperatures of 95 °F day/77 °F night (35/25 °C), but mature more slowly than when temperatures are warmer or cooler (Swanton et al. 2000).  Plants typically flower 5-8 weeks after emergence, with late emerging plants flowering most quickly (Kacperska-Palacz 1963, Vengris et al. 1966b, Norris 1996, Doll 2002, Shrestha and Swanton 2007), but very late (September) emerging plants are slow to flower (Norris 1996).  A few seeds may become viable at the milk-soft dough stage as early as 5 days after flowering (Sung et al. 1987).  Most seeds become viable three weeks after flowering (Vengris et al. 1966b).

Pollination:  Barnyardgrass is primarily self-pollinated, but some wind mediated cross pollination also occurs (Maun and Barrett 1986).  Late in the season, flowers may self-pollinate while still wrapped in the sheath (Maun and Barrett 1986).

Reproduction:  A large plant may produce over 100,000 seeds, whereas a highly stressed individual may produce less than 10.  More typically, seed production is several thousand to several tens of thousands of seeds per plant (Maun & Barrett 1986, Bagavathiannan et al. 2012), but seed production of over 200,000/plant has been observed in a California sugarbeet field (Norris 1992).  The intensity of competition from the crop greatly affects seed production.  For example, plants emerging with corn produced 11,200 seeds/plant whereas those emerging at the 4 leaf stage produced only 200 seeds/plant (Travlos et al. 2011).  Barnyardgrass produced 1,500 to 5,000 seeds/plant when emerging shortly after planting corn, but production was considerably less when emerging a month or more later (Pannwitt et al. 2019).  Other studies have shown similar large reductions in seed production for plants emerging after the crop (Bosnic and Swanton 1997, Bagavathiannan et al. 2012).  Barnyardgrass seed retention was highly variable at soybean harvest in the south-central U.S. ranging from 89-91% in three trials to 2-55% in two other trials (Schwartz-Lazaro et al. 2021).

Dispersal:  Barnyardgrass has no inherent dispersal mechanism, and seeds become scattered around the mother plant.  As a weed, the primary dispersal mechanism is on farming equipment or in crop seeds.  The seeds are a common contaminant of crop seed (Maun and Barrett 1986), manure (Maun and Barrett 1986, Mt. Pleasant and Schlather 1994), and cotton gin waste (Norsworthy et al. 2009) and can be dispersed when these materials are used to fertilize fields.  Barnyardgrass seeds can float for several days (Barrett and Wilson 1983) and disperse in irrigation water (Wilson 1980) and probably also in flood water.  Seeds are dispersed by ducks (Mueller and van der Valk 2002) and other birds (Maun and Barrett 1986) and by the awns sticking to animal fur. 

Common natural enemies:  A weevil, Hyperodes humilus, has been reported to attack the growing point of barnyardgrass in Massachusetts and kill young plants (Rahn et al. 1968), but, generally, this weed has no important natural enemies.

Palatability:  The seeds are edible, and the plant is generally a good forage for livestock.  Japanese millet (E. frumentacea Link) is a cultivated variety of barnyardgrass that is grown for grain in tropical Asia and Africa, and is used as a fast growing forage and cover crop in the U.S.A. (Maun and Barrett 1986).  Under highly fertile conditions, nitrate may accumulate to levels that are toxic to livestock (Holm et al. 1977).

References:

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