By Mike Owen, Department of Agronomy
Isolated fields of glyphosate-resistant weeds are likely showing up in Iowa. While absolute "certification" of field-wide glyphosate resistance weed populations is currently underway, the occurrence of glyphosate resistance was inevitable — certain members of any weed population have the genetics to fight whatever strategy is used against them. The occurrence of isolated glyphosate resistant common waterhemp plants in Iowa was documented in 1998.
But we can still get ahead of the resistant weeds. We need to think like this: It's not broken and we need to fix it so it stays that way. By realizing the inevitable potential for the problem early and taking appropriate action, producers can create management plans that keep glyphosate-resistant weeds from advancing.
Globally, 15 weed species have evolved resistance to glyphosate, and it looks like the trend is increasing.
Resistant weeds can be in a field for up to two years before they are discovered. That is why it is important to fix the problem before you have it. Prevent resistant weeds from moving in and increasing in relative importance within fields, because once you have a problem it can be managed, but never totally fixed.
The benefits of glyphosate stewardship will be realized in improved profitability because eliminated weed competition means higher soybean yields. Weeds that aren't controlled early will affect crop yields and increase the general weed population which will become a significant problem for many years.
The Iowa Soybean Association (ISA) in partnership with Iowa State University (ISU) has published a guide, "Glyphosate Stewardship: Fix It Before It Breaks," to help soybean producers keep glyphosate-resistant weeds out of their fields…and keep yields up.
The publication discusses strategies for fighting resistance, including using soil applied herbicides in addition to glyphosate applications. Copies of "Glyphosate Stewardship: Fix It Before It Breaks" are available at no cost by calling Iowa Soybean Association at 515-251-8640.
Micheal Owen is a professor of agronomy and weed science extension specialist with responsibilities in weed management and herbicide use. Owen can be reached by email at firstname.lastname@example.org or by phone at (515) 294-5936.