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New Methods and Material for Weed Control

Robert Parker
Washington State University - Prosser

No new chemistry has been added to the arsenal for weed control in grapes in the last few years. In our program at Washington State University at Prosser, we have been looking at two products for possible use in the future. The two products are thiazopyr (Visor) from Rohm and Haas and azafenidin (Milestone) from DuPont. For weed control, both herbicides will probably be applied during the grape dormant period. In the one trial conducted at the Irrigated Agriculture Research and Extension Center in 2000 both herbicides were applied with glyphosate to control the winter annual weeds present at the time of application. Subsequent germinating winter annual and summer annual weeds were controlled through the growing season. The only serious weed problem in this vineyard was Canada thistle. Neither herbicide controlled that weed. Safety to the furrow irrigated grapes was good.

Milestone mixed with methylated seed oil was also evaluated as a material to burn back grape suckers. The herbicide had excellent contact activity on the suckers present without any apparent injury to the parent plant. The grape plants in both trials will be evaluated again in 2001 to determine if there is any subsequent injury from the 2000 treatments.