Downy brome thrives in all soils. This weed has an extensive shallow root system and roots with many hairs which enable the plant to extract much of the soil water. The plant tillers profusely depending on time of germination. In early spring, the plant continues to tiller, joints, and sets seed. A heavy infestation can produce as much as 400 lbs or 80,000,000 seeds per acre. Some seeds will remain viable more than two years when placed near the soil surface because of natural dormancy or unfavorable conditions for germination.
In medium-textured soils, the optimum seed depth for downy brome emergence is less than 1 inch; however, seedlings can emerge from a 4-inch depth. A downy brome density of 50 plants per square foot can remove soil water to the permanent wilting point to a depth of about 2.5 feet.
Downy brome is thus very competitive with winter wheat for soil water and nutrients. Under stress the plants can produce seed when they are only 1 to 2 inches tall. Plants under stress from tillage or harsh environments divert more of their photosynthetic capabilities to seed production than undisturbed plants or plants growing in more productive environments.
As a winter annual, downy brome is a constant threat to winter wheat, alfalfa, and rangeland. Heavy infestations of downy brome can reduce wheat yields 30 to 80 percent. Both yield and quality of alfalfa in infested fields often will be lowered. Overgrazed rangelands are more easily invaded by downy brome which reduces economic returns of the grassland.
Downy brome is a palatable grass before the seed heads emerge but becomes unpalatable with maturity. Mature downy brome can cause injury to livestock (lump jaw in cattle) by causing infection in the eyes or mouth. Mature plants are also a serious fire hazard.