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   Wednesday, November 26, 2014

Introduction

Downy brome (Bromus tectorum)is an aggressive, grassy weed that has invaded southwestern Saskatchewan. Other common names for downy brome are cheatgrass, cheat, downy chess and downy cheat. Its presence in the southwest and its ability to infect many habitats makes it a threat to winter and spring cereals, dryland hayfields, pastures and rangelands across southern and central Saskatchewan. Downy brome is designated as a Noxious Weed in Saskatchewan.

Downy brome was first introduced to Saskatchewan in the Maple Creek area around 1960, probably in contaminated hay or seed. Since the early 1960s downy brome has spread to infest 116 townships in 31 rural municipalities. Throughout the region downy brome is common in waste areas, along roadsides and in ditches, fence rows, shelterbelts and railroad rights-of- way.

Even when downy brome is controlled in the crop, infested rangelands, pastures, roadsides, and waste areas throughout the southwest provide a continuing source of downy brome seed for reinvasion of winter wheat crops.

Identification

Downy brome is an annual grass that typically germinates in the fall and overwinters as a small seedling. Plants resume growth early in the spring.

Downy brome is easily distinguished from other grasses in the seedling stage by its very hairy leaves. Downy brome can be confused with fall rye in the seedling stage as both plants are purplish in colour, but fall rye has small hooks, called auricles that encircle the stem at the base of the leaf blade. Downy brome does not have auricles.

Japanese brome (Bromus japonicus) is less abundant that downy brome in Saskatchewan, but it is also a potential problem weed. It is very difficult to distinguish the two bromes in the seedling stage, but Japanese brome tends to grow in wetter sites than downy brome. Both species are very shallow rooted compared to cereal crops and once the heading stage is reached the species are easily separated. Downy brome has an open drooping panicle with long straight awns attached to the seed. Japanese brome has a panicle with the spikelets borne at the ends of long branches. Japanese brome seed is somewhat shorter than downy brome seed and has a twisted awn. Downy brome seed is a reddish colour at maturity while Japanese brome is tan in colour.

Biology

Downy and Japanese brome are both winter annuals which typically germinate in the fall in response to rain, but if fall moisture is not adequate they can act as spring annuals. Most downy brome seed is present in trash or on the soil surface. Accumulation of trash on the soil surface favours germination and establishment of downy brome. Thus continuous cropping and zero or minimum tillage production systems provide ideal conditions for the germination and emergence of downy brome. In fields with heavy trash cover downy brome readily germinates within the trash and on the soil surface and quickly emerges.

Fall emerged downy brome resumes growth very early in the spring and usually heads out in April or May. Plants from seeds that germinate in the spring normally do not produce seed in the same year but must first overwinter. Downy brome becomes very conspicuous at heading as the plants have a silvery sheen and, as they mature, take on a reddish-purplish appearance. The seed matures from mid-June to mid-July and is shed from the plant on maturation.

Control and Containment

Since downy brome reproduces only by seed, successful control can be achieved by preventing seed production and exhausting the soil seed bank. Seed spread is primarily through contaminated grain, hay, straw, manure and farm machinery. The long awn attached to the seed aids in sticking to animal fur, so seed is also likely spread by birds, antelope, deer and small rodents.

In cultivated land the best strategy is to prevent the initial infestation. This can be achieved by ensuring that any seed purchased is certified free of downy brome and by thoroughly cleaning equipment, particularly swathers and combines. Rotation to a spring cereal with at least one cultivation prior to seeding can be an effective control strategy. The spring seedbed preparation should kill any downy brome that germinated either in the previous fall or early spring. If a winter cereal is grown exclusively, then downy brome must be controlled in the fallow year using either cultivation or herbicides.

On rangelands and pastures farmers should be diligent and remove downy brome plants when the infestations are small because no herbicides are registered for control on rangelands. Preventing infestations is probably the best method for excluding downy brome from grazing and hayland.

Please refer to Saskatchewan Agriculture's Guide to Crop Protection for current herbicide rates and application recommendations.

Additional Information

Downy Brome - A Potential Problem in Winter Wheat. 1989.
Univerisity of Saskatchewan Publication No. 477

Managing Downy Brome in Crops and Pastures. 1991.
Agriculture Development Fund New Ideas.

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