You plan years ahead for crop rotation, fertilizer and machinery acquisitions. Since the rise of glyphosate-resistant weeds, you should be doing the same for your herbicide program, says Lisa Behnken, a Minnesota Extension crops specialist.

She urges growers to devise a multi-year plan to increase herbicide diversity. Adding multiple, effective modes of action and rotating herbicides are “key steps to prevent resistant weeds from gaining a foothold on your farm.”

Purdue University weed scientists Travis Legleiter and Bill Johnson suggest a similar exercise to help diversify weed control. “We encourage growers to go after herbicide management from a long-term standpoint,” says Legleiter.

Look back 2 or 3 years at your past chemical use, Behnken suggests. “Look for red flags,” such as repeated use of the same products and over-reliance on a postemergence program.

Next, Behnken says, write out herbicide plans for the next two seasons, targeting the worst weeds in each field. Study herbicide performance charts from your local Extension service or herbicide distributor.

Then record the site of action for each herbicide you’ve selected. That’s the specific biochemical pathway that the herbicide uses to disrupt plant growth. North Central weed scientists publish a “Corn and Soybean Herbicide Chart” that lists sites of action for individual herbicides and premixesat

This information is also on herbicide labels. Tally the sites of action your plan deploys: How many are effective against your target weeds?

Now take a critical look at your plan, Behnken says. A diversified herbicide program should:

  • Use at least two or three effective sites of action against your worst weeds
  • Avoid overusing any site of action in a single growing season
  • Rotate herbicides so you are not using the same sites of action consecutively

An ideal herbicide program maximizes the number of effective sites of action without using any site of action more than twice in a growing season, Legleiter says. “Three or more passes of the same site of action really raises selection pressure.”