Guidelines to Prevent Herbicide-Resistant Weeds

• Scout fields before applying any herbicide to determine the species occurring and if economic levels justify a herbicide application.
• Use alternative weed management practices, such as mechanical cultivation.
• Rotate crops with an accompanying rotation of herbicides to avoid repeat use of herbicides with the same mode of action on the same field.
• During a single growing season, limit the number of applications of a single herbicide or combination of herbicides with the same mode of action.
• Mix or sequentially treat using herbicides that each control the weeds in question, but have different modes of action.
• Scout fields after application to detect weed escapes or shifts.
• Clean equipment before leaving fields suspected to have resistant weeds.
• Rotate glyphosate with other herbicides.
• Don’t use more than two applications of a glyphosate-based herbicide in any given field over a two-year period.
• Use alternative burndown chemistry for Roundup-Ready fields likely to require more than one over-the-top application.
• Use the RR system that best fits your farming operation.
• Use full rates of glyphosate to minimize tolerant escapes.
• Do not allow weed escapes to produce seeds or vegetative propagules.
• In RR corn, control weeds before 3” – 4” in height to protect yields from early season weed competition. Plan to make 2 applications of glyphosate to maintain control through canopy if you don’t use a preemergence herbicide.
• If a grower prefers to use two sequential applications of glyphosate over RR crops, then we recommend rotating to conventional seed technology and other herbicide options with a different mode of action the following year.

—Weed Science Society of America, Syngenta.

More information on weed resistance online: www.weedresistance.com