Plan your post-herbicide applications now
If you expect to make a postemergence herbicide application this season, remember that even small weeds can take a significant toll on corn yields. "The common recommendation is to remove weeds before they exceed 3" tall," says Aaron Hager, University of Illinois Extension weed scientist. Because most weeds can grow that much within a day or two, at the most, you need to prepare in advance so you’re able to spray at the optimum time.
Application delays will cost you crop yield, notes Dave Feist, development leader for MANA. "You’re trying to eliminate weed competition with the crop. This is an area where you can lose 10 bu. per acre very quickly," he says.
Consider these additional tips to help you get the most bang for your post-emergence herbicide buck.
Start clean. Don’t underestimate the value of having a clean tank system to start with, advises James Reiss, vice president of agricultural chemistries for Precision Laboratories. Along with that, make sure you match nozzle type to the herbicide or tank mix you plan to spray and replace any worn nozzles.
Consider crop growth stage. If you tank-mix products, follow the most restrictive label to determine the right crop growth stage restriction. This step can help you avoid potential crop injury, says Travis Legleiter, Purdue Extension weed scientist. Corn ear development can also be affected if postemergence herbicides are applied too late in the growing season.
"The type and amount of injury from an application beyond the labeled window is dependent upon the herbicide, other environmental stresses and the exact timing of application," Legleiter says.
Injury symptoms can include ear pinching, ear bottlenecking, internode stacking, onion leafing, rat tailing, brace root malformation and green snap, among others.
Here are several additional recommendations from Legleiter:
- Avoid using contact herbicides just prior to rain, or when there is a heavy dew, to avoid washing the herbicide down into the plant whorl.
- Avoid applying growth regulator herbicides if you have several nights in a row of temperatures that dip to 45°F or cooler.
- Do not use UAN solutions as the carrier when applying atrazine pre-mixes to spike stage corn.
- Do not mix growth regulator herbicides with chloroacetamide herbicides and apply postemergence. (These mixtures are fine if applied pre-emergence.)
- Do not apply ALS inhibitors past the V6 growth stage.
Make good coverage a priority. The better coverage you attain of existing weeds, the better control outcome you can expect, MANA’s Feist says.
In the process, make sure you use the recommended amount of carrier for the herbicide, that spray boom heights are accurate, and that application speed matches field topography.
"If you look behind you at the row as you spray, and the solution is moving off the crop, you’re going too fast and need to slow down," he advises.
"Keep in mind that good coverage of weeds improves control and will help your corn maximize its yield potential," he adds.
You can e-mail Rhonda Brooks at firstname.lastname@example.org.