Field experiments were conducted to determine the interaction of grazing and herbicide treatments on cheat control and biomass, wheat biomass, wheat grain yield, and wheat yield components. Ethyl-metribuzin at 1120 g ai ha−1 and metribuzin at 420 g ai ha−1 reduced cheat biomass 91 to 99 and 97 to 98%, respectively. Grazing had no effect on herbicide efficacy. Grazing increased cheat biomass in the check by 24% at only one location but did not affect total wheat plus cheat biomass. With one exception, controlled cheat was replaced by wheat on a 1:1 biomass basis when herbicides caused no crop injury. All herbicide treatments increased grain yield, but grazing did not alter yield. At two locations, increased heads m−2 and spikelets/head accounted for most of the grain yield increases, but at one location seeds/spikelet and weight/seed were also increased. Harvest index was unaffected.

Field studies were conducted for 4 yr to investigate the effects of tillage and herbicide programs on weed control and wheat (Triticum aestivum L. ‘Potomac’ in 1981 and ‘Wheeler’ from 1982 to 1984) grain yields in a wheat-soy bean [Glycine max (L.) Merr.] double-crop rotation. Predominant weed species were common chickweed [Stellaria media (L.) Vill. # STEME], corn chamomile (Anthemis arvensis L. # ANTAR), and annual bluegrass (Poa annua L. # POAAN) at the onset of research and cheat (Bromus secalinus L. # BROSE) and soft brome (Bromus mollis L. # BROMO) at the conclusion of the study. Control of all species was excellent with conventional tillage and no-till plus nonselective herbicides but was significantly less with no-till without nonselective herbicides and with minimum tillage. After 4 yr, maximum wheat grain yields were significantly higher in conventional- than in minimum- or no-till systems.

Field experiments were conducted in 1982 through 1986 to evaluate the effect of six postemergence grass herbicides, clethodim, the methyl ester of diclofop, the butyl ester of fluazifop-P, the methyl ester of haloxyfop, the methyl ester of quizalofop, and sethoxydim, on 31 seedling grass species. All herbicides except diclofop controlled most of the species tested. None of the herbicides controlled rattail fescue or red fescue. Only clethodim and haloxyfop controlled annual bluegrass.

Field experiments were conducted to determine the influence of winter wheat seeding date and forage removal on the efficacy of cheat control herbicides, forage and grain yields, and net returns to land, overhead, risk, and management for the various cheat control strategies. Economic analysis showed that net returns were higher when wheat was seeded during the traditional seeding period (October) than when either seeded early (September) for increased forage production or delayed (November) for cultural cheat control. Some herbicides were economically beneficial at two of three locations where the initial cheat population exceeded 170 plants/m2.

A study was conducted at two locations to evaluate the effects of cheat (Bromus secalinus L. ♯3 BROSE) competition on four seeding rates (4.5, 9.0, 13.5, and 22 kg/ha) of alfalfa (Medicago sativa L. ‘Riley’). Three stages of first harvest (early bud, early bloom, and late bloom) were imposed on fall-planted alfalfa, with and without cheat overseeding, to determine the effects of harvest stage on alfalfa yield and quality. Cheat infestations significantly decreased alfalfa production and forage quality. Increasing the seeding rate of alfalfa only partially offset these losses. Harvesting early helped minimize the effect of cheat competition. First-harvest protein yield of forage was significantly decreased by, cheat overseeding. Total protein yield at first harvest was not affected by cutting stage but did increase with the two higher seeding rates of alfalfa.

Field and growth chamber experiments were conducted from 1983 to 1985 to determine the relationships between loss in plant productivity and plant residue-crop-weed density in no-till wheat (Triticum aestivum L.) and to document chemical management and cultivar options for such a cropping system. Untilled stubble left on the soil at rates of 0.5 and 3 t/ha reduced wheat density and grain yield in continuous winter wheat. Stem densities of cheat (Bromus secalinus L. # BROSE) and downy brome (B. tectorum L. # BROTE) in mulched treatments averaged about 682, 679, and 38 stems/m2 in 1983, 1984, and 1985, respectively. In the nonmulched treatment, weed density and standing dry matter ranged from 5 to 30 stems/m2 and 2 to 6 g/m2, respectively. Removal of residues eliminated key habitat characteristics required for the establishment of Bromus spp. Preemergence and early postemergence applications of BAY SMY 1500 [4-amino-6-(1,1-dimethylethyl)-3-(ethylthio)-1,2,4-triazin-5(4H)-one] at 2 kg/ha controlled both species of Bromus in no-till wheat. The herbicide treatment slightly delayed maturity of 10 wheat cultivars, but control of cheat and downy brome allowed nine cultivars to attain their yield potential, improving grain yield over that of untreated plots. ‘Vona’ wheat did not tolerate the herbicide and was susceptible after emergence. BAY SMY 1500 widens the spectrum of weed management and wheat cultivar options for an annual conservation production system of winter wheat.

Bioassays using binary mixtures that included a cover crop with known allelopathic potential and a weed species were employed to determine the importance of allelopathy compared to resource competition as interference mechanisms. Responses of weed species germinated with cover crops in a petri dish were measured. Interference between weed and cover crop seedlings was determined in a greenhouse experiment using the additive design, which included partitions to reduce above- and below-ground competition and used capillary mat subirrigation to control moisture and fertilizer availability. Germinating sorghum reduced radicle length of weeds, whereas germinating rye tended to increase weed radicle length. Methods limited above-ground competition, so likely interference mechanisms were below-ground competition and allelopathy. Germination with a cover crop had little effect on germination and shoot length of weeds. Increased density of rye but not of sorghum reduced growth of barnyardgrass seedlings. Reduced number of barnyardgrass leaves in the presence of rye was likely due to allelopathy. Suppression of barnyardgrass dry weight attributed to allelopathic interference by rye was successfully separated and compared to the combined effects of competition and allelopathy.

Greenhouse studies determined the dose-responses of cheat, downy brome, Japanese brome, jointed goatgrass, and winter wheat to preplant-incorporated MON 37500 and its residual effects on kochia. Concentrations of MON 37500 up to 60 ppbw did not affect winter wheat. MON 37500 did not prevent weed emergence, but increasingly inhibited weed growth as the dose was increased up to about 20 ppbw. GR50 values were 16, 16, 11, and 31 ppbw for cheat, downy brome, Japanese brome, and jointed goatgrass, respectively. Japanese brome was more susceptible than cheat or downy brome, and jointed goatgrass tolerated two to three times more MON 37500 than the Bromus species. Plant dry weights of kochia seeded after removal of the winter annual grasses decreased with increasing initial MON 37500 concentrations up to 20 ppbw. Kochia density was influenced by which winter annual grass was grown previously.

Experiments were conducted in an environmentally controlled growth chamber to determine the effects of temperature (10/5 or 21/7 C, day/night), soil moisture (7, 14, or 20%), timing (preemergence [PRE] or postemergence [POST]), and rate (9 or 18 g ai ha−1) of application on MON 37500 efficacy on Bromus secalinus L. and toxicity to Triticum aestivum L. MON 37500 reduced B. secalinus plant density an average of 40% but did not reduce T. aestivum density. PRE treatments reduced B. secalinus density 40% compared to 12% with POST applications when plants were grown at 10/5 C. Soil moisture level also influenced plant density, with 7.9 plants per pot when soil moisture was maintained at 7%, compared to 8.5 plants per pot with 14 or 20% soil moisture. MON 37500 reduced B. secalinus dry weight more at 18 g ha−1 than at the 9-g ha−1 rate when grown at 21/7 C, but no rate response occurred at 10/5 C. PRE applications of MON 37500 at 10/5 C decreased B. secalinus dry weight 22% more than PRE applications at 21/7 C or POST applications under either temperature regime. However, PRE applications of MON 37500 at 21/7 C decreased T. aestivum biomass an average of 16%, compared to 3% or less with other treatments. At 21/7 C, B. secalinus dry weight decreased 46% as soil moisture increased from 7 to 20%. Bromus secalinus was 10 to 12% less susceptible to MON 37500 when grown at 7% soil moisture at 10/5 C than when grown at the same temperature at 14 or 20% soil moisture. Triticum aestivum injury was greater at 20% soil moisture under each temperature regime.

The methyl ester of diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} mixed with soil at 1, 2, and 3 ppmw reduced the growth of Bromus species in the greenhouse as follows: downy brome (Bromus tectorum L. ♯ BROTE) more than Japanese brome (Bromus japonicus Thunb. ex Murr. ♯ BROJA) more than cheat (Bromus secalinus L. ♯ BROSE). The decrease in herbicide effect (decay) over time was described better using a second-order equation than a first-order equation. Plant response-herbicide dose relationships were described best with a cubic polynomial equation.

Seven field experiments were conducted in Oklahoma to compare efficacy and wheat response to currently registered cheat suppression or control herbicide treatments. Chlorsulfuron + metsulfuron premix (5:1 w/w) at 26 g ai/ha applied PRE controlled cheat 20 to 61%, increased wheat grain yields at two of seven locations, and decreased dockage due to cheat at five of seven locations. Chlorsulfuron + metsulfuron at 21 g/ha tank-mixed with metribuzin at 210 g/ha, applied early fall POST, controlled cheat 36 to 98% and increased wheat yield at four of seven locations. Metribuzin applied POST in the fall at 420 g/ha controlled cheat 56 to 98% and increased wheat yields at five of seven locations. Both POST treatments decreased dockage at all locations.

Ten field experiments were conducted in Oklahoma from 1988 to 1992 to evaluate chlorsulfuron plus metsulfuron (5:1 w/w) and triasulfuron for cheat control in winter wheat. Cheat control by chlorsulfuron plus metsulfuron at 18 and 26 g ai/ha varied from 0 to 81% and by triasulfuron at 18 and 30 g ai/ha from 0 to 60%. Grain yield was increased in four experiments and dockage was reduced in five experiments by both rates of chlorsulfuron plus metsulfuron.

Thirteen field experiments were conducted to evaluate quinclorac for cheat control in hard red winter wheat. Cheat control with quinclorac was variable. Quinclorac at 560 and 1120 g a.i./ha applied to tillered wheat controlled cheat 93 to 100% at four sites. In contrast, pooled over four other experiments and four application times, quinclorac at 420 g/ha and 560 g/ha controlled cheat only 20 and 31%, respectively. Quinclorac at 420 g/ha plus chlorsulfuron:metsulfuron (5:1) at 35 g a.i./ha applied PRE increased wheat yield 28% at one of three sites. At two of these sites, averaged over chlorsulfuron:metsulfuron rates of 0, 18, and 35 g a.i./ha, quinclorac at 280 and 420 g/ha applied POST, increased wheat yield 32 to 112%. In two cultivar tolerance experiments, quinclorac treatments did not damage any cultivar. Pooled over cultivars, yields were increased 7 and 10% when quinclorac at 280 and 560 kg/ha was applied, respectively. In a greenhouse experiment, quinclorac plus dicamba or esfenvalerate consistently reduced the leaf area of cheat in a manner suggesting synergistic effects. Of eight adjuvants evaluated in a laboratory experiment, only quinclorac plus the adjuvant BCH 864 01S reduced cheat leaf area more than quinclorac alone.

Twenty field experiments were conducted in Oklahoma from 1983 through 1986 to evaluate the ethylthio analog of metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(ethylthio)-1,2,4-triazin-5(4H)-one] for selective control of cheat (Bromus secalinus L. #3 BROSE), downy brome (Bromus tectorum L. # BROTE), and rescuegrass (Bromus catharticus Vahl. # BROCA) in winter wheat (Triticum aestivum L.). The ethylthio analog of metribuzin applied postemergence at 1.1 kg ai/ha before the weeds tillered controlled 91 to 100% of these Bromus spp. in winter wheat. Control of tillered Bromus spp. was less consistent. As Bromus spp. control increased, wheat yields increased, and dockage decreased. The herbicide was selective on wheat over a wide range of soils, including sands. Adding surfactant to very early postemergence applications of 0.6 kg ai/ha increased cheat control but injured wheat slightly. Surfactant use had little or no effect on dockage reduction and yields.