Downy Brome Densities Research Articles

Downy Brome (Bromus tectorum L.) and Broadleaf Weed Control in Winter Wheat with Acetolactate Synthase-Inhibiting Herbicides

A study was conducted for three seasons in northwest Kansas, USA to evaluate acetolactate synthase (ALS)-inhibiting herbicides for downy brome (Bromus tectorum L.) and winter annual broadleaf weed control in winter wheat. Herbicides included pyroxsulam at 18.4 g ai ha−1, propoxycarbazone-Na at 44 g ai ha−1, premixed propoxycarbazone-Na & mesosulfuron-methyl at 27 g ai ha−1, and sulfosulfuron at 35 g ai ha−1. The herbicides were applied postemergence in fall and spring seasons. Averaged over time of application, no herbicide controlled downy brome more than 78% in any year. When downy brome densities were high, control was less than 60%. Pyroxsulam controlled downy brome greater than or similar to other herbicides tested. Flixweed (Descurainia sophia L.), blue mustard [Chorispora tenella (Pallas) DC.], and henbit (Lamium amplexicaule L.) control did not differ among herbicide treatments. All herbicides tested controlled flixweed and blue mustard at least 87% and 94%, respectively. However, none of the herbicides controlled henbit more than 73%. Fall herbicide applications improved weed control compared to early spring applications; improvement ranged from 3% to 31% depending on the weed species. Henbit control was greatly decreased by delaying herbicide applications until spring compared to fall applications (49% vs. 80% control). Herbicide injury was observed in only two instances. The injury was ≤13% with no difference between herbicides and the injury did not impact final plant height or grain yield.

Role of Size and Nitrogen in Competition between Annual and Perennial Grasses

AbstractDiffering life histories contribute to difficulties establishing perennial grasses on lands dominated by exotic annual grasses. In a greenhouse study, we investigated to what extent allowing the perennial grass bluebunch wheatgrass to emerge before the exotic annual grass downy brome would increase its competitive ability and whether modifying nitrogen (N) would affect competition. We conducted an addition-series factorial experiment. In three cohort treatments, the two species were seeded concurrently or bluebunch wheatgrass was at the two- or four-leaf stage when downy brome was planted. N treatments were low (ambient) or high (N added to maintain 10 mg kg−1 [0.1286 oz lb−1]). Larger bluebunch wheatgrass avoided suppression by downy brome regardless of N. Under concurrent sowing, doubling downy brome density decreased bluebunch wheatgrass biomass by 22.6% ± 2.38 SE. In contrast, when bluebunch wheatgrass had a four-leaf size advantage, the same increase in downy brome density decreased bluebunch wheatgrass biomass by 4.14% ± 2.31. Larger bluebunch wheatgrass also suppressed downy brome more effectively, but N enrichment decreased the suppressive ability of bluebunch wheatgrass.

Cropping Systems to Control Winter Annual Grasses in Winter Wheat (Triticum aestivum)

Field studies were conducted from 1990 through 1997 to evaluate the long-term effect of 2- and 3-yr rotations on the control of downy brome, jointed goatgrass, and feral rye in winter wheat. At the completion of the study, jointed goatgrass and feral rye densities averaged 8 plants/m2and < 0.1 plant/m2for the 2- and 3-yr rotations, respectively. Downy brome densities averaged < 0.5 plant/m2for both the 2- and 3-yr rotations, with no treatment differences observed. Winter annual grasses were not eradicated after two cycles of the 3-yr rotations, but weed densities were reduced 10-fold compared to densities after one cycle and more than 100-fold compared with the 2-yr rotations. Wheat grain contamination with dockage and foreign material followed a similar trend. The 3-yr rotations were economically competitive with 2-yr rotations and provided superior control of the winter annual grass weeds.

MON 37500 rate and timing affects downy brome (Bromus tectorum) control in winter wheat (Triticum aestivum)

Field experiments were conducted at five locations in Colorado, Kansas, and Wyoming in 1994–1995 and 1995–1996 to compare the effects of MON 37500 rate and application timings on downy brome control and winter wheat tolerance. MON 37500 at 18 to 35 g ha−1applied preemergence or fall postemergence reduced downy brome density 71 to 92% in 1995. Spring-applied MON 37500 suppressed downy brome growth but did not reduce plant density. No application reduced downy brome density in 1996. At each location, downy brome was controlled best by MON 37500 applied preemergence or fall postemergence at 35 g ha−1. MON 37500 did not affect wheat height at Archer or Torrington, WY, and Burlington or Stratton, CO, but wheat treated preemergence or fall postemergence was taller than untreated wheat at Hays, KS, in 1995. Spring-postemergence-treated wheat at Hays in 1995 was shorter than untreated, preemergence-, or fall-postemergence-treated wheat. Wheat head density did not differ among treated and untreated plots at Torrington, but herbicide treatment increased wheat yields. Wheat head density increased with all MON 37500 treatments at Hays in 1995, as did yield. However, preemergence and fall-postemergence applications resulted in the highest wheat yields. No herbicide treatment affected head density or yield at Hays in 1996.

Downy Brome (Bromus tectorum) Emergence Variability in a Semiarid Region

This study characterized seedling emergence of downy brome from August to early December over a 6-yr period. Seedlings were counted weekly in quadrats established in winter wheat stubble at Akron, CO. Seedling emergence varied among years, which was caused by erratic seasonal precipitation. Producers delay planting of winter wheat to reduce downy brome density in the crop, but in only 1 yr out of 6 would producers have benefited from this control strategy. Furthermore, delayed planting has negative crop consequences: less grain yield and more susceptibility to plant diseases and wind erosion because of less fall plant growth. Because fall precipitation is erratic in the semiarid Great Plains, other control strategies, such as nitrogen placement and increased seeding rates of winter wheat, would be more effective for downy brome management, yet not detrimental to winter wheat production.

Effects of fertilizer and stubble burning on downy brome competition in winter wheat

Abstract Increased downy brome (Bromus tectorum) infestation is one of the dominant impediments to adoption of conservation tillage. Surface residues often increase grassy weed competition and lower the yield of cereal crops. Crop residue and fertilizer placement effects on downy brome growth and nutrient uptake in relation to that of winter wheat (Triticum aestivum L.) were conducted in two separate years; one involving conventional (plow) tillage and the other no‐till. Crop residue (burning versus no burning) and fertilizer placement (broadcasting versus subsurface banding) differentials were present both years. The conventional‐till study also included nitrogen (N) rates from 0 to 168 kg/ha and an N only versus nitrogen+phosphorus+sulfur (N+P+S) comparison. Burning increased early‐spring wheat growth substantially, with only limited effect on downy brome population or growth. Broadcasting of fertilizer increased downy brome density and growth compared to banding. Wheat, in contrast, had greater growth and higher N uptake from banded fertilizer. Increasing N increased both seedling survival and culm production of downy brome. Addition of N+P+S increased both wheat and downy brome growth more than N applied alone, but wheat appeared more responsive. Wheat yield tended to be less with higher downy brome infestation.

Rotation Affects Downy Brome (Bromus tectorum) in Winter Wheat (Triticum aestivum)

Downy brome control in winter wheat is often inadequate. The effects of three crop rotations and two tillage intensities on downy brome populations and associated crop yields were determined in an experiment at Lethbridge, Alberta from 1987 to 1993. Downy brome densities in continuous winter wheat increased from 24 to 970 plants/m2between 1988 and 1993; and were often higher with zero tillage. Inclusion of fallow or spring canola in rotation with winter wheat suppressed downy brome densities to less than 55 and 100 plants/m2, respectively, over the six years. In continuous winter wheat, yields decreased as downy brome densities increased progressively over years, indicating that monoculture winter wheat production will not be viable in regions where downy brome is prevalent unless effective herbicides are developed. In the more arid areas of the Canadian prairies, a winter wheat-fallow rotation may be most suitable but in higher precipitation areas, a winter wheat-canola rotation is a viable alternative. Crop rotation is a key component of an improved management system for control of downy brome.

Downy Brome (Bromus tectorum) Interference in Winter Rye (Secale cereale)

Field experiments over 3 yr at Lethbridge, Alberta, determined the effect of various downy brome densities and times of its emergence on winter rye biomass and seed yield. Downy brome reduced yields most when it emerged within 3 wk of rye, but densities of more than 100 downy brome m-2were required to reduce yields by 20 to 30%. The greatest reductions in rye biomass (28%) and seed (33%) yields over the 3 yr occurred when 400 downy brome m-2emerged with the crop. Downy brome, at densities up to 400 plants m-2, emerging 6 wk after rye or in early spring, reduced rye biomass and seed yield less than 10% in all years. Winter rye effectively shaded downy brome (40 to 90%) for much of the growing season.

Downy Brome (Bromus tectorum) Density and Relative Time of Emergence Affects Interference in Winter Wheat (Triticum aestivum)

Field experiments over 3 yr at Lethbridge, Alberta, determined the effect of various downy brome densities and times of its emergence on winter wheat biomass and seed yield. Downy brome reduced wheat biomass up to 59% and seed yield up to 68%. Time of downy brome emergence relative to wheat affected the magnitude of these yield reductions more than the density of downy brome. At comparable densities, downy brome caused 2- to 5-fold greater reductions in yield when it emerged within 3 wk after winter wheat than when it emerged 6 wk after wheat or in early spring. Late-emerging downy brome caused significant wheat yield or biomass losses only at densities of 200 to 400 plants m-2. Late-emerging downy brome plants were strongly shaded (70 to 90%) by winter wheat throughout much of the growing season.

Downy Brome (Bromus tectorum) Interference and Economic Thresholds in Winter Wheat (Triticum aestivum)

Densities up to 100 downy brome m2were established in winter wheat in southeastern Wyoming and west-central Kansas to quantify wheat yield loss from downy brome interference and to approximate economic threshold levels. A quadratic equation best described wheat yield loss as a function of weed density when downy brome emerged within 14 days after wheat emergence. Densities of 24, 40, and 65 downy brome m2reduced wheat yield by 10, 15, and 20%, respectively. Wheat yield was not reduced when downy brome emerged 21 or more days later than wheat. Economic thresholds varied with changes in downy brome density, cost of control, wheat price, and potential wheat yield. In a greenhouse experiment, dry weight of 72-day-old wheat plants grown in association with downy brome was not affected by the distance between the weeds and wheat, whereas downy brome plant dry weight increased with increasing distance between the weeds and wheat.

Downy Brome (Bromus tectorum) Control in Winter Wheat

Metribuzin at 0.42 kg ai/ha and metribuzin plus terbutryn at 0.28 plus 0.67 kg/ha were applied in the fall and spring to control downy brome in winter wheat from 1981 through 1985. Downy brome control averaged 88% from the fall-applied treatments and 63% from the spring-applied treatments. Yields from the fall- and spring-applied treatments averaged 136% and 132% of the check, respectively. Metribuzin plus terbutryn fall-applied controlled downy brome best (93%), and wheat yields were significantly higher than the checks in all experiments. Moreover, as downy brome density among locations increased, wheat yields decreased.

Integrated Systems for Control and Management of Downy Brome (Bromus tectorum) in Cropland

Downy brome (Bromus tectorumL. # BROTE) may be a troublesome weed in winter small grains, perennial legumes, perennial grasses grown for seed, and orchards. In Nebraska, winter wheat (Triticum aestivumL.) yields have been depressed 30% by downy brome populations of 11 to 22 plants/m2(8). In Oregon, downy brome densities of 108 to 160 and 538 plants/m2reduced yields by 40 and 92%, respectively (22, 23). In Idaho, wheat yields were depressed 20 to 40% with 55 to 110 plants/m2(18). Downy brome has also been shown to lower yields and quality of hay from infested fields of alfalfa (Medicago sativaL.) (29). In perennial grass seed fields, downy brome may cause a serious seed quality problem (16). Some grass seed lots have contained as much as 50 to 75% downy brome seed.

Competition Between Winter Wheat and Downy Brome

Four experiments were conducted to develop controls for downy brome (Bromus tectorum L.) in winter wheat (Triticum aestivum L. ‘Gaines’). In three experiments downy brome was removed at monthly intervals from emergence to harvest. In the third and fourth experiments, hand weeded and weedy controls were compared to chemical control with R11913 (3′-hydroxypropionanilide isopropylcarbamate). Downy brome, which emerged with wheat, was most competitive during March of each year. For maximum effectiveness, R11913 should be applied when downy brome has less than one to three tillers or chemical control will be erratic. On a silt loam soil with an average annual precipitation of 42 cm, downy brome densities of 108 to 160 plants/m2 lowered wheat yields 6% when competition was eliminated by March. When competition was permitted until wheat harvest (July), yield was reduced 40%.