Integrated Management of Downy Brome in Winter Wheat

Integrated Management of Downy Brome in Winter Wheat

PNW668
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Drew Lyon, Extension Small Grains Weed Scientist, Washington State University, Andrew Hulting, Extension Weed Science Specialist, Oregon State University, Don Morishita, Extension Weed Science Specialist, University of Idaho, Frank Young, Research Agronomist, USDA-ARS, Pullman, WA
Downy brome (Bromus tectorum L.), also known as cheatgrass, is especially troublesome in low precipitation production areas where crop rotations are mostly limited to winter wheat followed by a year of summer fallow. The invasive weed is best controlled with a combination of management tools to reduce a plant population to an acceptable level while preserving the quality of natural resources.
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Introduction

Downy brome (Bromus tectorum L.), also known as cheat- grass, was introduced into North America from the Mediterranean area of Europe. It was first identified in the eastern United States in 1861, and by 1914 this invasive weed had spread throughout the continent. Downy brome is adapted to climates with annual precipitation ranging from 6 to 22 inches. It can colonize both disturbed and undisturbed sites with a wide range of soil conditions.

Downy brome is a major weed problem in winter wheat (Figure 1). In eastern Washington, 54 downy brome plants per square foot reduced winter wheat yield by 92 percent (Rydrych and Muzik 1968). Downy brome is especially troublesome in low precipitation production areas where crop rotations are mostly limited to winter wheat followed by a year of summer fallow.

Downy brome is best controlled in wheat using integrated weed management (IWM). This approach involves a combination of management tools to reduce a weed population to an acceptable level while preserving the quality of natural resources.

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Identification

Downy brome is a winter annual grass that ranges from  12 to 24 inches in height at maturity. The seed head is 2–6 inches long, with 5–8 spikelet flowers (Figure 2). Magnification reveals greater detail of the ½ inch long seeds and their ½–¾ inch long awns (Figure 3), as well as the fine hairs on the leaf sheaths and blades (Figure 4).

Biology

Downy brome seed germination typically occurs in autumn shortly after the onset of rains when the soil temperature is about 70°F. Seeds can continue to germinate at soil temperatures between 35° and 40°F if soil moisture is adequate. Established plants overwinter in the vegetative stage, resume rapid growth in the early spring, and mature in May or June (4–6 weeks before winter wheat).

Downy brome can also be produced from seeds germinating in the spring, although seed production is much more prolific from autumn-germinating plants. Newly mature downy brome seed requires a short after-ripening period for optimum germination. After-ripening, a process that

Figure 1. Downy brome infestation in a winter wheat–fallow crop rotation. (Photo by Drew Lyon)
Figure 2. Mature downy brome plant showing slender, erect culms (tillers) supporting dense, slender, drooping panicles (seed heads) with spikelets of flowers. (Photo by Larry Burrill, formerly with Oregon State University)

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