Autumn mowing may cut herbicide need

Agricultural Research, May, 2004 by Michael F. Carpinelli

Russian knapweed is a problem in ranges and pastures in the western United States, where it grows up to 4 feet tall and takes over otherwise productive land. Once established, Russian knapweed may be difficult to control. Currently, most producers apply chemicals on rangeland in spring or summer, when knapweed begins to flower, but research is showing that fall application may be preferable.

On two study sites in eastern Oregon, tests were done using a new piece of equipment that mows and applies herbicide in a single pass. They showed that mowing just before herbicide application puts more herbicide on the intended target--the soil surface. Rains later carry the herbicide into the root zone, and from there it's drawn up by growing weeds the following spring. Its degradation is slowed by the low soil temperatures of fall and winter.

Though most farmers don't mow their weeds, the added cost of this measure may be offset by a reduced need for herbicide, and the knapweed might be more effectively controlled. Michael F. Carpinelli, USDA-ARS Range and Meadow Forage Management Research Unit, Burns, Oregon; phone (541) 573-8911, e-mail michael.carpinelli@oregon state.edu.