Soybean Checkoff Funds Glyphosate-Resistant Horseweed Survey

Barbara Scott, Weed Science Research Associate, University of Delaware

In November 2004, over 20% of DE soybean farmers responded to a University of Delaware Weed Science survey. The objectives of the survey were to determine: 1) how many DE soybean farmers encountered glyphosate-resistant horseweed, 2) what, if any, crop management changes were made and if the level of horseweed control had since changed, and 3) what are grower perceptions of Roundup Ready® (RR™) crops in light of glyphosate-resistant horseweed. Survey results showed that glyphosate-resistant horseweed continues to be problematic in the First State.

The vast majority of the survey population (98%) reported using both glyphosate and RR soybeans at some point in the last five years, with 90% planting RR soybeans three or more years. Of these respondents, 38% (81 of 213 farmers) reported having an experience with glyphosate-resistant horseweed. Even though 94% of those that encountered resistance made one or more changes in soybean management practices, only 37% reported a decrease in the severity of the infestation. No single management strategy or combination of strategies provided consistent horseweed control.

Many farmers (59%) reported that the presence of glyphosate-resistant horseweed decreased the value of RR technology, and 78% agreed that it was worthwhile to incur greater short-term costs in order to preserve glyphosate herbicide for future use. Yet, of the survey population, 70% reported that horseweed control was not a greater concern than control of any other weed associated with no-till soybeans. At the present the attractiveness of glyphosate herbicide is clear as 91% of farmers reported their use of glyphosate had either remained constant or increased over the last five years. Based on survey results, DE soybean farmers currently feel the benefits of glyphosate (and RR technology) continue in the presence of glyphosate-resistant horseweed.

Gary King, Manager, Indian River Marina; Bob Metz, 1st V.P., American Soybean Association; Jeffrey Allen, President, Delaware Soybean Board; Charles Salkin, Director, Delaware Parks and Recreation; Michael Scuse, Delaware Secretary of Agriculture; Janice Dahl, Executive Director, United Soybean Board; Douglas Corey, Mark Wilson, and Dee Watson, Jr., Directors, Delaware Soybean Board; Robert Baker, President, Delaware Farm Bureau.