KTIC Radio Extension Corner: Late Herbicide Applications in Soybeans

This is Dr. Nathan Mueller, your local agronomist with Nebraska Extension for Dodge and Washington counties. Do I still need to control weeds in my soybean field? Is it too late to apply the herbicide I have? Can I switch to another herbicide product? These are all important questions to answer.

Let’s talk about three important things you need to do:

Determine the soybean growth stage
Read the herbicide label so you know the latest in-season application allowed
Reduce your risks, including crop injury, unacceptable pesticide residue, monetary fines, and herbicide carryover issues

Agronomist have developed a standard growth staging system to clearly communicate how mature a soybean plant is. Soybean height is not a good way to determining maturity or how late you can apply a given postemergence herbicide. For example, full bloom or the R2 growth stage is when there is a flower or bloom is found on the one of the top two uppermost nodes with fully expanded leaves of the plant on 50% of the plants. If you do not have a new Nebraska Soybean and Corn Pocket Field Guide – 2017 Edition – please visit your local Nebraska Extension office to pick up a free copy. This pocket guide will help you determine your soybean growth stage.

You need to read the label for each soybean herbicide you will be applying to check at what soybean growth stage it can be applied up to or what preharvest interval exist. For example, some of the PPO inhibitors like Cobra and Phoenix have a 45 day preharvest interval. However, some products like Extreme, Pursuit, and Raptor must be applied prior to flowering, R1 growth stage.

Applying after these latest allowed growth stages, the herbicide can cause injury and yield loss to the soybean crop. If you apply herbicides in the window narrower than preharvest interval allowed, the harvested crop may have unacceptable pesticide residue levels which could cause problems in livestock and our food chain. Monetary fines for off-label applications can occur too. Lastly, late herbicide applications can increase chances of carryover herbicide issues in winter wheat or a cover crop and to the next spring cash crop like alfalfa or corn.

So know you soybean growth stages, read the herbicide label, and reduce your risks. To listen to this radio message again and to get more information, visit our local website at croptechcafe.org or give me a call at 727-2775. Know your crop, know your tech, know your bottom line. This is Dr. Nathan Mueller, your local agronomist for Nebraska Extension on KTIC radio.

Additional Information and Resources: