Controlling Western Ragweed in Pasture

Controlling Western Ragweed in Pasture

May 18, 2007

Western ragweed (Ambrosia psilostachya) is a native weed commonly found 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 seeds and rhizome. Rhizome is a horizontal creeping root system growing in the top 5-10 inches of soil surface.

Plants usually grow in sparse groups (patches or clusters). The stem is very erect, up to 3 feet tall, with many branches and long hairs that give it a coarse feeling. Leaves are alternate on the upper part of the stem and 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. Western ragweed, in Nebraska, 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.

Western ragweed provides forage for deer and its fruits are an important food source for upland gamebirds, wild turkeys and songbirds. Native Americans made a tea from the whole plants 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 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 one to two times a season, depending on the amount of rainfall. One mowing in mid June is effective if the season is dry, due to lack of moisture needed for weed regrowth. If the season is wet, an additional mowing is needed in July-August.

Herbicides also can be effective in providing season long control. Herbicides should be applied when ragweed plants are 3-5 inches tall. Some effective herbicides and their rates are: 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

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