Seven tips to stop spread of weed resistance

Maybe your Achilles heel is marestail. Or perhaps it’s giant ragweed. Whatever weed you fear may become resistant, Danny Greene offers tips to thwart future spread of resistance. Greene, a certified crops adviser, operates Greene Consulting Inc., Franklin.

Some other experts also added tips.

Key Points

If you don’t have a weed problem in some areas, don’t spray.

Make scouting a part of your weed control program.

Control any problem weeds in nearby noncrop areas.


Use herbicides only when needed. You may find parts of fields don’t need a post-application if you applied a residual early. Just because you have glyphosate-tolerant or LibertyLink corn doesn’t mean you have to spray every acre.

Rotate herbicides with different modes of action. Don’t use a herbicide with the same mode of action back-to-back. Check the Purdue University Corn & Soybean Field Guide to make sure you’re applying herbicides with different active ingredients. See pages 169-172. Dig further to makes sure modes of action are different.

Tank mix herbicides with different sites of action. Look for two herbicides you can mix together that kill the weed in different ways. It limits how fast resistance can build up.

Rotate crops, including those with different life cycles. A corn-soybean rotation where you apply glyphosate or Ignite each year certainly doesn’t help the resistance cause. Instead, mix in a crop where a herbicide with the same mode of action won’t be applied two years in a row.

Don’t overlook tillage options where appropriate. Tom Bauman, Purdue University weed control specialist, reminds that hard steel, such as a cultivator, is still an effective tool against weeds if you’re not in no-till.

Scout to know where weeds are problems. Jason Webster, an Illinois CCA with Beck’s Hybrids, Lexington, Ill., says many farmers don’t have a step-by-step scouting program. If someone doesn’t want to scout by walking whole fields, an aerial-based imaging program may help identify sources of problems that need to be ground-truthed by walking to GPS-identified spots. Beck’s Hybrids used Crop Health Imaging for its own use, and also offers the service to customers at a fee.

However, in many cases you may need to scout before an aerial image would identify the problem. Crop Health Imaging typically produces images later in the season. If weeds escaped, it might help identify where they’re located, but it would take another season before you could gain control.

Clean equipment to avoid weed seed transport. Shattercane is the classic weed that’s easy to track if it’s spread by a combine. If you’re spreading shattercane, you may also spread resistant weeds. Take time to clean out equipment after leaving an infested field.

Keep problem weeds out of adjoining noncrop areas. Roadsides, field borders and ditch banks are notorious places for weeds to multiply. If it’s a resistant weed, it will continue producing resistant seed. Jeff Nagel, Ceres Solutions, Lafayette, says the key to reducing the seed bank over time to prevent a resistant weed, such as giant ragweed, is to not let it go to seed.

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Rowdy or resistant? These ragweeds weren’t resistant to Ignite. They just hadn’t been sprayed yet. A spray mix with Ignite and tankmix partners took them out.

This article published in the February, 2011 edition of INDIANA PRAIRIE FARMER.

All rights reserved. Copyright Farm Progress Cos. 2011.