Submitted to: Eastern Oregon Agricultural Research Center
Publication Type: Experiment Station
Publication Acceptance Date: 1/1/2004
Publication Date: 6/29/2004
Citation: Carpinelli, M.F. 2004. Effect of mowing prior to applications of picloram and clopyralid on Russian knapweed control. Eastern Oregon Agricultural Research Center. Range Field Day Report 2004: Current Forage and Livestock Production Research. Special Report 1052. P. 40-44.
Interpretive Summary: Russian knapweed is a perennial weed that forms dense colonies by adventitious shoots arising from an extensive root system. It infests some of the most productive pasture and hayland of the Great Basin. Fall application of a soil-active herbicide may be an effective way to control Russian knapweed growth the following year. Recently developed equipment mows and applies herbicide in a single pass, removing standing dead plants and allowing more herbicide to reach the soil where it is taken up by plant roots. In a recently completed study, we tested two soil-active herbicides with and without mowing. Generally, Russian knapweed control using either herbicide was improved where preceded by mowing. This method may increase profits to hay and forage growers by reducing herbicide costs while improving control of Russian knapweed.
Technical Abstract: Russian knapweed is a perennial weed that forms dense colonies by adventitious shoots arising from an extensive root system. It infests some of the most productive pasture and hay land of the Great Basin. Fall application of a persistent, soil-activated herbicide has been shown to effectively control Russian knapweed. The objective of this study was to investigate if mowing prior to a fall herbicide application improved herbicide efficacy on Russian knapweed. The Brown Brush Monitor mows and applies herbicide in a single pass, removing standing dead plants and allowing more herbicide to reach the soil surface. Using the Brown Brush Monitor, two persistent, soil-active herbicides (picloram and clopyralid) were tested with and without mowing at two sites in southeast Oregon. Treatments were applied in fall 2001, and Russian knapweed control, density, and height were measured in summers 2002 and 2003. Results were inconsistent at Site 1. At Site 2, mowing increased Russian knapweed control by clopyralid in 2002 and by picloram in 2003, and reduced Russian knapweed height and density for both herbicides in 2003. Results from this study suggest that control of Russian knapweed may be improved by mowing prior to fall herbicide application, but that results may be site-specific.