Controlling Cool-Season Invaders

Controlling Cool-Season Invaders

October 23, 2009

Cheatgrass, downy brome, bluegrass, smooth brome and other cool-season plants have invaded many warm-season grass pastures and rangeland. This invasion shifts good grazing away from summer and toward spring when most folks have plenty of pasture anyway.

Cool-season grasses take over summer pastures relatively easily because they develop rapidly during fall and spring when native grass provides little competition. Then they use moisture and nutrients during spring before warm-season plants have a
chance to use them.

Hard grazing this fall after the recent freezes as well as early next spring will weaken brome and bluegrass when warm-season plants are dormant and unaffected. This can stop further invasion and slowly improve summer production. A prescribed spring burn also can do wonders for a warm-season pasture if you have enough fuel to carry a fire and can conduct the burn safely and legally.

Maybe the fastest approach, though, is to apply glyphosate herbicides like Roundup in late fall. Recent hard freezes have turned warm-season plants dormant but weedy cool-season grasses are still green. For best results apply glyphosate when daytime temperatures are above 60°F and nighttime temperatures stay above 40°F. This will kill or weaken the green and susceptible cool-season grasses but not affect dormant warm-season plants. By reducing competition, warm-season plants will grow more vigorously next year and provide better summer pasture.

Bruce Anderson
Extension Forage Specialist