Two weeds, downy and Japanese brome, are spreading across North Dakota at an alarming rate, according to a North Dakota State University (NDSU) weed specialist.

"Downy brome especially is causing concerns and has been found across the southern third of the state," says Kirk Howatt, assistant professor of weed science at NDSU.

Both weeds often are more common in cropland than other brome species. In the seedling stage, the two plants are very difficult to tell apart. The plants are more easily distinguished once the seed heads emerge because Japanese brome has a very wide, compact arrangement of seeds in the panicle, compared with the very long, slender seed arrangement of downy brome.

They emerge in the fall or very early in the spring and often are reaching reproductive stage before spring crops are sprayed for weeds. Plants might emerge after preplant weed desiccation, but a cold period is required for seed production. Downy brome tends to mature earlier than Japanese brome, which makes downy brome more difficult to control.

"Downy brome that emerges in the fall can produce a seed head by the end of May," Howatt says. "Herbicides will have better activity on young plants, so herbicides applied in the fall or very early in spring are necessary when tillage is not an option."

Glyphosate will control young plants, but plants with seed heads emerging are more tolerant. ACCase inhibitors, such as Puma, Discover and Achieve, often give poor control of Japanese and downy bromes, but Assure II, Select and Poast provide excellent control of nonstressed plants up to full tillering.

ALS-inhibiting herbicides provide good to excellent control, depending to a large degree on precipitation, as well as the specific herbicide. In wheat, Maverick and Olympus have activity on bromes, but producers need to consider the residual activity of these herbicides, which may prolong the intervals before seeding many crops in North Dakota.

Everest and Beyond (Beyond can be used only on Clearfield
wheat) also have good activity on these bromes, and the rotation intervals are much shorter. Beyond and Raptor are registered in several other crops but will be effective only on late emerging bromes in many crops because of the timing of herbicide use. In corn, herbicides with activity on bromes include Option and Basis.

"It might be too late to significantly affect the brome population in your field this year," says Howatt. "It is important for producers to scout their fields to determine if they have Japanese or downy bromes and then create a plan for getting after the weeds this fall and next season."