Competition between downy brome (Bromus tectorum) and winter wheat causes serious economic losses to growers in the Pacific northwest. On a site which received 25 cm average annual rainfall and had a light soil (very fine sandy loam) winter wheat yields were reduced 28% by fewer than 54 downy brome plants per m2 (5 plants/ft2). On a site which received 55 cm average annual precipitation and had a silt loam soil, winter wheat yields were reduced 92% by more than 538 downy brome plants per m2 (50 plants/ft2). Downy brome seed‐to‐straw ratios were indicative of a tremendous yield potential. Seed‐straw ratios of 1:4 are probably an exception but ratios of 1:1 and 1:2 were common. Chemical fallow studies at three sites showed that nonselective downy brome control can be obtained by the use of herbicide combinations such as 3‐amino‐l‐2, 4‐triazole‐ammonium thiocyanate (amitrole‐T), plus chloro‐4‐ethylamino‐6‐isopropylamino‐s‐triazine (atrazine) or amitrole‐T plus 2,4‐dichlorophenoxyacetic acid (2,4‐D). Amitrole‐T plus atrazine was more effective when used as a fall treatment. Amitrole‐T plus 2,4‐D was more effective in the spring. These chemicals reduced tillage requirements and decreased downy brome growth by 90%.

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%.

Above-ground seedling development was characterized for five annual grass weeds: downy brome, bulbous bluegrass, jointed goatgrass, Italian ryegrass, wild oat; and three cereals: winter wheat, winter barley, and winter triticale in field experiments over two years. The rate of leaf production on the main stem of each species was linearly related to cumulative growing degree days (GDD) since planting. Leaf production rates were faster for bulbous bluegrass, downy brome, Italian ryegrass, wild oat, and barley than for wheat, triticale, and jointed goatgrass. The main stem development stage when individual tillers appeared was similar in all species except under poor seedbed conditions in 1991, in which case lower-node tillers were delayed in the cereals and jointed goatgrass, but not in most of the weed species. Bulbous bluegrass, downy brome, and barley had the same percentage of plants produce the first four primary tillers on the main stem in both years; the other species showed more year-to-year variation. Seedling heights at full emergence were generally greater for large-seeded species. Small-seeded species compared to large-seeded species tended to have greater relative increases in plant height over time. Knowledge of comparative development rates between these weeds and cereals could provide information for development of growth models for each of the species and could also improve understanding of the competitive relationships between grass weeds and cereal grains.

This article describes one model for organizing and mobilizing scientific resources to address the highly complex and costly problem of soil erosion in the Pacific Northwest. With a U.S. Department of Agriculture grant to the agricultural experiment stations in Washington, Oregon, and Idaho, as well as supplementary state and federal funds, STEEP awards intermediate-term (15 year) grants for research in five areas: tillage and plant management, plant design, erosion and runoff predictions, pest management, and socioeconomics of erosion control. Most of the research projects require collaboration across disciplines and, in some instances, across state boundaries. After 6 years of effort the results obtained with STEEP indicate that the model might be applicable to other regions and problems.

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