Downy and Japanese Brome pose a growing threat on the prairies

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By Trevor Lennox, Regional Forage Agrologist with Saskatchewan Ministry of Agriculture

Downy and Japanese brome grasses have become serious pests on the southern Prairies. These invasive annual weeds pose a significant threat to native grasslands, infest tame perennial pastures and are an issue in winter cereal production. More recently, Japanese brome has created problems in spring-seeded crops in Saskatchewan.

Historically, downy brome and Japanese brome have been viewed as winter annuals occurring together in mixed populations in the traditional area of adaptation. However, there are more and more incidences of these bromes germinating in the spring as an annual weed. The weeds have taken advantage of reduced tillage and continuous cropping in grain fields and capitalized on feed movement in livestock operations to travel across the west.

Downy brome prefers semi-arid areas. It will survive well on both poor and fertile soil but is typically found in the brown and dark brown soil zones. Japanese brome prefers moister and more fertile soil found in all soil zones. It does not tolerate soil salinity.

Difficult identification often leads to one or the other being mislabelled. However, control measures are similar for both so the taxonomy question is often moot. Japanese brome is more sensitive to herbicides than its downy cousin. Both downy and Japanese bromes are prolific seed producers.

The weakest link in the life cycle of these annual bromes is that the seeds don’t persist in the soil very long. Research studies have shown that over 90 percent of the downy brome weed seeds were no longer viable past their second year. Therefore if seed production can be stopped for a period of two to five years, it is possible to make good progress in controlling this weed.

On annual cropland, a pre-seeding burn off with Glyphosate will knock out both of these bromes. Also take any opportunity to control late-germinating seedlings in the fall. In crop weed control may also be required to control later flushes of downy and Japanese brome. For herbicide options consult the ‘Guide to Crop Protection’ for recommendations.

It is very important to clean up invasive brome problems prior to seeding perennial forages, as chemical control options are very limited. When dealing with grass and grass/alfalfa mixtures producers have to resort to cultural controls such as hand pulling, early grazing prior to seed set, or baling and burning of weed infested hay patches. Do not transport the weed infested hay. Planting a mixture of competitive forages can improve plant competition, and including at least one creeping rooted species can further help displace the invasive bromes. On pure alfalfa hay stands, there are a few chemical options that can help displace downy brome from the forage stand.

Two additional articles on downy and Japanese brome can be found on the Saskatchewan Ministry of Agriculture website:, and do a quick search for the articles titled: “Grassy Weed – Downy Brome” and “Problem Weeds – A Cattlemen’s Guide”. For further information contact Trevor Lennox, Regional Forage Agrologist with Saskatchewan Ministry of Agriculture at 306-778-8294, or

Organizations: Saskatchewan Ministry of Agriculture

Geographic location: Southern Prairies

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