Controlling Western Ragweed in Pasture

Controlling Western Ragweed in Pasture

June 1, 2007

Western ragweed (Ambrosia psilostachya) is a common native weed in northeast Nebraska's rangeland, prairies and disturbed sites in all soil types. It is a perennial forb from the sunflower family (Asteraceae) that reproduces both by seed and rhizome.

Plant description

Rhizome is a horizontal creeping root system growing in the top 5-10 inches of soil. The plants usually grow in sparse groups (patches or clusters). The stem is very erect, up to 3 feet tall, and has many branches with long hairs that give it a rather coarse feeling. Leaves are alternate on the upper part of the stem, opposite on the bottom, with many divisions and teeth. Like many other plant species, the overall growth and development depends on the amount and timing of rainfall. In Nebraska western ragweed can flower from July to October, with greenish-yellow flowers positioned on the top of the main stem and branches. It produces inch long bur-like fruits with a single seed within each bur.

Uses

Western ragweed provides forage for deer and the fruits are an important food source for upland game-birds, wild turkeys and songbirds. Native Americans made a tea from the whole plant to treat colds and cramps. Western ragweed has almost no value to livestock because of its low palatability. With other forage limited, it may be eaten. Pollen produced in late summer causes "hay fever" in many people, due to the presence of volatile oils, which can also cause skin irritation.

Control

Mowing. Due to its low value for livestock forage, it is a concern to livestock producers and ranchers. This weed can be controlled by various means. Mowing the plants when they are 4-6 inches tall can reduce ragweed population considerably. Plants can be mowed once or twice per season, depending on the amount of rainfall during the season. One mowing in mid June is effective if the season is dry, since little moisture will be available for regrowth. If the season is wet, an additional mowing is needed in July-August.

Chemical. Herbicides also can be effective in providing season-long control. Herbicide application should be conducted when ragweed plants are 3-5 inches tall. The list of effective herbicides and their rates per acre includes: Salvo (12 oz/ac), 2,4-D-Ester (1qt/ac), Grazon P+D (32 oz/ac), Weedmaster (32 oz/ac), Ally (0.25 oz/ac), and Vista (22 oz/ac).

Stevan Knezevic
Extension Weeds Specialist
Haskell Ag Lab, Northeast REC

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