Ethyl ester of DPX-Y6202 {2-[4-[(6-chloro-2-quinoxalinyl)oxy] phenoxy] propanoic acid} and butyl ester of fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} applied during the reproductive phase of development at 0.07 and 0.28 kg ai/ha prevented seed formation in downy brome (Bromus tectorum L. # BROTE). Fluazifop prevented seed formation over a wider range of application rates and growth stages than did DPX-Y6202. Seed production was prevented most readily by herbicide applications made early in the reproductive phase. Environmental factors during reproduction affected herbicide performance. Foliar absorption and translocation of 14C-fluazifop into the developing spikelets was greater than that of 14C-DPX-Y6202 in downy brome.

Field studies were conducted from 1986 through 1989 to determine the feasibility of using clomazone in a winter wheat-corn-fallow rotation. Clomazone at 1.1 kg ai/ha did not control emerged downy brome in autumn nor did it control redroot pigweed and tumble pigweed that emerged after a spring application of paraquat at 0.6 kg ai/ha. However, clomazone plus atrazine at 0.6 plus 2.2 kg ai/ha provided weed control in winter wheat stubble from October to corn harvest 12 mo later. Corn yields from this treatment were equal to or greater than the conventional practice of applying atrazine plus glyphosate at 2.2 plus 0.4 kg ae/ha in the fall followed by a spring application of metolachlor plus dicamba at 2.8 ai plus 0.3 kg ae/ha. When kochia densities were high, clomazone plus atrazine controlled triazine-resistant kochia better than metolachlor plus dicamba. Atrazine at 2.2 kg/ha applied in autumn followed by clomazone at 0.8 kg/ha in April generally caused more corn injury than when the same rate of clomazone was applied in autumn with the atrazine. The percent of bleached corn plants varied with planter, year, time of application, and rate of clomazone applied. The optimum time to apply clomazone at 0.6 kg/ha was in autumn with atrazine. This treatment caused some corn bleaching but produced the highest corn yield over 3 yr. In a dry autumn and spring, less clomazone injury occurred with a planter equipped with row cleaners than those without. The injury pattern associated with planters was inconsistent when precipitation was average and no injury occurred in a wet autumn and spring.

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−1 applied 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.

Field experiments were conducted in 1992 and 1993 to determine the timing and amount of rainfall required to activate UCC-C4243 applied preemergence. UCC-C4243 at 0, 70, and 140 g ai ha−1 was applied 1, 7, 14, and 21 d before 0.5 or 2 cm of simulated rainfall. Temporary rainshelters protected field plots from natural rainfall during the 21 d dry period. Herbicide activity was determined in the field by seeding lentil, wheat, common lambsquarters, and field pennycress and in the greenhouse by a sugarbeet bioassay of soil samples (0 to 3 cm depth) taken from all plots immediately before irrigation. UCC-C4243 did not injure wheat; however, lentil population was reduced when simulated rainfall occurred within 7 d after application. Lentil injury was greater with higher herbicide rate and higher water level. UCC-C4243 at 70 and 140 g ha−1 reduced populations of both weed species by 75 and 90%, respectively, when either 0.5 or 2 cm simulated rainfall was received within 1 d after herbicide application. Weed control was reduced with a 21 d delay between herbicide application and water activation. The sugarbeet bioassay showed a linear decrease of herbicide activity over time and also with accumulated photosynthetically active radiation. After 17.9 d, herbicide activity on a dry soil surface decreased 50%. Laboratory investigations show that [14C]-UCC-C4243 on glass slides was photodegraded by near ultraviolet light (290 to 400 nm). Volatilization of 14C-labeled herbicide from glass slides was less than 5% after exposure to turbulent air for 48 h.

Rhizobacteria are being evaluated for promotion of plant growth and for biological control of weeds, insects, diseases, and nematodes. Although considerable efforts have been allocated to this approach to biological control, commercial success remains elusive yet intriguing. In this review, the root biology of downy brome and winter wheat is described as an initial model of the information needed for other plant hosts. A limited review of rhizobacteria in disease management is presented to demonstrate the potential and some limitations with rhizobacteria as biocontrol agents. Several techniques are described to improve the survival of a rhizobacterium to suppress downy brome. To achieve success with rhizobacteria in pest management, more information is needed on the root biology of the host plants and the ecology of the rhizobacteria.

Field studies were conducted to determine if varying the time N fertilizer was applied would affect downy brome interference in winter wheat. Five treatments were compared: four broadcast application times of NH4NO3 at 56 kg N ha-1 during the fallow-crop cycle: 1) during fallow; 2) at planting; 3) during crop dormancy; 4) before winter wheat jointing; and 5) a control where no N was applied. Downy brome was least responsive to N applied during fallow. All N applications during the growing season of winter wheat increased downy brome biomass and culms m-2. Downy brome interference prevented winter wheat from responding positively to N. For example, when crop season precipitation was only 70% of normal, applying N reduced grain yield of winter wheat infested with downy brome from 12 to 28%. This study indicates that N manipulation offers potential for reducing downy brome interference in winter wheat.

Immediately following postemergence application, similar quantities of metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] were retained on the foliage of downy brome (Bromus tectorum L. # BROTE) and winter wheat (Triticum aestivum L.). Three days following treatment, more metribuzin was present on the surface of the foliage of downy brome than of winter wheat and similar quantities of metribuzin had been absorbed into the interior of the foliage of both species. Fourteen days after treatment, metribuzin had disappeared from the surfaces of the foliage of both species but more metribuzin was present in the interior of the foliage of downy brome than of winter wheat. Results from petri dish studies in the field suggested that the amount of unaltered metribuzin available for absorption by leaves was influenced primarily by volatilization and secondarily by photodecomposition. In addition, small quantities of rainfall may have washed metribuzin from leaf surfaces. In 1984, yield of winter wheat was greater in metribuzin-treated plots than in nontreated check plots.

Tebuthiuron was evaluated at two Wyoming locations for its effects on big sagebrush control and associated vegetation, Big sagebrush was controlled with tebuthiuron at 0.6 to 1.1 kg ai/ha. Green needlegrass, prairie junegrass, blue grama, and Douglas rabbitbrush were unaffected by tebuthiuron treatments. Western wheatgrass and downy brome increased at different study locations and were dominant grass species at the end of 7 yr.

The influence of pH on the behavior of metribuzin and ethyl-metribuzin in soil and nutrient solution was studied. Toxicity of both herbicides to oats decreased as soil pH decreased from 8.4 to 4.2 in a sandy loam. Herbicide adsorption increased as soil pH decreased. In nutrient solution, pH did not change the phytotoxicity of either herbicide, indicating that pH primarily influences herbicide availability in soil and not plant uptake.

A Bromus tectorum L. (downy brome) biotype with cross-resistance to sulfosulfuron has been identified. The resistant biotype was selected with primisulfuron in Poa pratensis L. (Kentucky bluegrass) plots near Madras, OR. The plots received two treatments of 20 g ai ha−1 primisulfuron in the fall of 1993, 1994, and 1995. In 1995, control of B. tectorum decreased and greenhouse studies confirmed that the biotype was resistant to primisulfuron. Cross-resistance to sulfosulfuron also was confirmed in greenhouse studies. Metabolism of sulfosulfuron rather than an insensitive site of action is the likely cause of the cross-resistance.

In separate studies in west-central Kansas, a prepackaged mixture of chlorsulfuron + metsulfuron (5:1 w/w) and triasulfuron alone or in combination with metribuzin as a sequential or tank mix treatment were evaluated two years for downy brome control in winter wheat. Downy brome and wheat responses to each herbicide alone PRE or plus metribuzin POST varied between years. Visually, downy brome biomass was reduced 32 to 79% by chlorsulfuron + metsulfuron at 16 to 26 g ai/ha and 58 to 76% by triasulfuron at 30 g ai/ha applied PRE. Metribuzin POST at 158 g ai/ha following chlorsulfuron + metsulfuron PRE at 26 g/ha and metribuzin POST at 140 g/ha or more following triasulfuron PRE at 30 g/ha reduced downy brome biomass in both years more than PRE treatments alone. Chlorsulfuron + metsulfuron at 11 or 16 g/ha plus metribuzin at 105 or 158 g/ha applied POST affected downy brome less in 1992 than chlorsulfuron + metsulfuron applied PRE at 21 or 26 g/ha. Conversely in 1993, POST treatments except for chlorsulfuron + metsulfuron at 11 or 16 g/ha plus metribuzin at 105 g/ha affected downy brome more than PRE treatments. Triasulfuron plus metribuzin POST in late fall controlled downy brome better than a sequential application in one of two years; late-fall POST was better than early-spring POST applications in both years. Despite some treatments retarding growth, no treatment in either study reduced wheat yield in 1992. However in 1993, chlorsulfuron + metsulfuron PRE at 26 g/ha, chlorsulfuron + metsulfuron at 16 g/ha plus metribuzin at 105 or 158 g/ha applied POST, and metribuzin POST at 315 g/ha reduced wheat yields. Triasulfuron at 30 g/ha plus metribuzin at 140 g/ha or higher applied PRE, sequentially, or POST in late fall and metribuzin applied POST in early spring at 280 g/ha also reduced wheat yields.

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.

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.

Field experiments were conducted to determine suitable application timings and rates of MON 37500 for downy brome control in winter wheat. MON 37500 applied preemergence (PRE) or in fall postemergence (POST) provided better control of downy brome than when applied spring POST. MON 37500 at rates ranging from 19 to 33 g ai/ha applied PRE or fall POST controlled downy brome >85%. MON 37500 applied spring POST at 60 g/ha only suppressed growth of downy brome. Winter wheat was not visibly injured and maturity was not delayed by MON 37500 applied up to 60 g/ha at any of the application timings. Winter wheat yield responded positively to all MON 37500 treatments but PRE or fall POST applications usually resulted in greater yields than spring POST applications. Wheat yields progressively increased with increasing rates of MON 37500 up to 30–40 g/ha, above which yields tended to plateau or, in two instances, decline slightly. MON 37500 is an important new herbicide that should enable growers to better manage downy brome in winter wheat production systems.

In the greenhouse, glyphosate [N-(phosphonomethyl)glycine] at 0.6 kg ae/ha applied directly to seeds alone or seeds on the soil surface reduced germination and shoot dry weight of common rye (Secale cereale L. ♯3 SECCE). Paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) applied similarly at 0.6 kg ai/ha reduced germination and shoot dry weight of downy brome (Bromus tectorum L. ♯ BROTE) and wheat (Triticum aestivum L. ‘Daws' ♯ TRZAX). Metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5 (4H)-one] at 0.6 kg ai/ha applied to seeds, soil, or seeds and soil had very little effect on germination, but significantly reduced shoot dry weight of common rye, downy brome, wheat, and jointed goatgrass (Aegilops cylindrica Host. ♯ AEGCY). Pronamide [3,5-dichloro(N-1,1-dimethyl-2-propynyl)benzamide] at 0.6 kg ai/ha, and propham (isopropyl carbanilate) at 3.4 kg ai/ha plus extender (p-chlorophenyl-N-methylcarbamate) at 0.4 kg ai/ha substantially reduced shoot height and dry weight of all species, regardless of application method, with pronamide completely inhibiting shoot elongation and dry-weight production in three of the four species.

The control of western juniper (Juniperus occidentalis Hook.) trees released shrub and herbaceous vegetation from dominance of the tree overstory. Revegetation of the woodland with desirable browse and forage species required weed control of both shrub and herbaceous species. The method of tree control (herbicidal, mechanical, or wood harvesting) influenced subsequent weed control-revegetation options in the understory. Physical restraints imposed by standing dead trees resulting from picloram (4-amino-3,5,6-trichloropicolinic acid) treatment limited the use of weed control and seeding equipment. Accumulation of litter interfered with the use of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] for annual grass control on both the picloram and wood harvest plots. Establishment of forage species was most successful on the mechanically cleared plots. Attempts to revegetate with browse species were largely foiled by native herbivores, and selective predation occurred on herbaceous species.

Two experiments were conducted near Scottsbluff, NE, to evaluate the efficacy of fall-and spring-applied herbicides for downy brome control in established alfalfa. Downy brome was effectively removed from established alfalfa, and alfalfa yield increased with fall applications of hexazinone, metribuzin, pronamide, and terbacil. Regression analysis indicated a linear relationship between alfalfa yield and downy brome biomass. Glyphosate or paraquat suppressed downy brome when applied to dormant alfalfa in the spring. If glyphosate or paraquat application was delayed until after alfalfa had resumed spring growth, injury was observed. Alfalfa yield did not increase following spring applications of glyphosate or paraquat.

Greenhouse and growth chamber experiments were conducted to evaluate primisulfuron phytotoxicity to downy brome (Bromus tectorum) and Kentucky bluegrass (Poa pratensis) as a function of herbicide placement, adjuvants, and environmental conditions. Primisulfuron rates needed to produce GR50 (50% growth reduction) values were 0.97 ± 0.57 and 8.07 ± 1.85 g/ha for downy brome and Kentucky bluegrass, respectively. Primisulfuron was applied to downy brome and Kentucky bluegrass at three placement sites: foliar, soil, and foliar plus soil. Foliar or foliar plus soil applications were more effective at reducing downy brome dry weights than the soil application of primisulfuron, whereas Kentucky bluegrass was injured more from the soil or foliar plus soil applications than from the foliar application of primisulfuron. Primisulfuron at 5 g/ha applied alone reduced downy brome dry weights by 5%, whereas when an adjuvant was added, dry weights were reduced by 52 to 83%. Primisulfuron was more phytotoxic to downy brome at alternating temperatures of 8 to 16 C and 16 to 24 C than at 0 to 8 C. Phytotoxicity of primisulfuron was less when downy brome plants were stressed for soil moisture after herbicide treatments than when the plants were not stressed or only stressed before treatment.

Seedling vernalization was more effective than seed vernalization in promoting flowering of downy brome (Bromus tectorum L. # BROTE). Vernalizing imbibed downy brome caryopses at 3 C for 0 to 30 days did not induce rapid flowering when the caryopses were planted. Downy brome seedlings were exposed for 30 days to six photoperiod/temperature treatments. After subsequent transfer to long days, plants from the short-day/3 C treatment flowered within 30 days. Flowering was delayed or was absent in treatments with higher temperatures or long days. The shoot apex increased in volume during the short-day/3 C vernalization period. Two days following vernalization, floral initiation had occurred. By day 5, lateral organs had proliferated. Rudimentary glumes and lemmas were visible by day 8.

Preemergence and postemergence application of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)-one] at 0.6 and 1.1 kg ai/ha controlled downy brome (Bromus tectorum L. ♯ BROTE) in winter wheat (Triticum aestivum L. ‘McDermid’) but caused considerable injury without the use of activated carbon over the seeded row. Activated carbon applied in 5-cm bands over the seeded row at 84, 167, and 336 kg/ha protected winter wheat at Pendleton on a silt loam soil. On a sandy loam soil, only a 336 kg/ha rate provided protection from metribuzin. Metribuzin toxicity to winter wheat was more difficult to neutralize when applied preemergence. Downy brome control was not reduced by carbon applied over the wheat row. The best treatment in this study was carbon at 336 kg/ha applied preemergence over the row followed by metribuzin at 0.6 or 1.1 kg/ha postemergence. A 10-week delay between preemergence carbon banding and postemergence metribuzin protected winter wheat from chemical injury.