Cheatgrass (Downy Brome)

  • Cheatgrass (Downy Brome)

    The term ‘cheatgrass’ is often used to describe various annual brome species. Locally, cheatgrass refers to downy brome and Japanese brome collectively, both species found throughout Larimer County below 9,000 feet. Downy brome is the more prominent of the two grasses. Dense stands of dry plant material create a fine-fuel source for frequent summer wildfires in the western United States.

    Growth Habit – Cheatgrass species follow a winter annual life cycle – seed germinates following late summer or early fall moisture (some spring emergence can occur as well), becomes dormant in winter, and is the first grass to green-up in the spring. Cheatgrass typically sets seed in May and dries down by July. Cheatgrass proliferates following summer wildfires that eliminate desirable plants and create openings for cheatgrass emergence with late summer rains. Also, fire removes the thatch layer that can disrupt an herbicide’s effectiveness.

    Identification– Cheatgrass plants grow from 6 to 24 inches tall, depending on available soil moisture, fertility and plant competition. At emergence, leaves are brownish-green. Mature plants are red-brown in color and have erect and slender stems. Leaf sheaths and flat, twisting blades are covered with soft hair. Leaves are approximately 1⁄32 inch wide and 2 to 6 inches long. Panicles are 2 to 6 inches long with slender branches that droop to one side. It has numerous, five-to-eight-flowered spikelets with ⅜ to ⅝ inch awns that are slender, straight and purple at maturity. Each awn is attached to the lower lemma of a hairy, buffbrown, ½ inch long and narrow seed. Roots are fibrous, relatively shallow, and grow many hairs which enable the plants to extract soil water very effectively.

    Reproduction – At maturity, the abundant and very prickly seed heads become a nuisance to hikers, pets and livestock. Cheatgrass is a prolific seed producer. Seeds become germinable soon after maturation, but typically do not remain viable for more than two or three years.


    • The most common herbicide for controlling cheatgrass is imazapic (Plateau/Panoramic).
    • Treatments should be applied in the fall either pre-emergent or early post emergent (prior to the tillering stage of the grass).
    • Glyphosate (Roundup and others) can be applied at low rates in the winter when perennial grasses are dormant for selective control.
    • No insect biocontrol agents are available for control of cheatgrass. Grazing in the early spring when the grass is palatable can suppress seed head production, but can also be injurious to desirable perennial grasses at that time.
    • Hand pulling or tillage (where feasible) is effective if conducted prior to seed set. Mowing is marginally effective, as re-growth will occur and plants will set seed from a reduced height.