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Northern Illinois Agriculture

University of Illinois Extension
Weeds Kub

Late season weeds

Posted by Russel Higgins - Weeds

This has been a challenging year to control weeds in corn and soybean fields in northern Illinois. In some fields early season rains prevented intended soil applied herbicides. Our wettest June on record compounded issues by delaying post applications. Drowned out areas in fields are now  populating with weeds including pigweed species, Giant ragweed and grasses. With much of the grain fill period for both crops ahead of us, immediate options available to oversize weeds are limited. The 2015 Ohio, Indiana and Illinois Weed Guide shares the following Harvest Aid options. Note that the herbicides recommend that the crops have reached physiological maturity before application.

Corn
  • Aim - (carfentrazone) can be applied prior to harvest of corn for dessication of velvetleaf, morningglory, pigweeds, and other weeds. Apply at least 3 days before harvest when the crop is mature and grain has begun to dry down.
  • Glyphosate - Many glyphosate products can be applied as a preharvest treatment to control perennial and annual weeds in corn. Application rate varies with glyphosate product, type of application (ground vs aerial), type of corn (glyphosate-resistant corn vs other), and amount of glyphosate previously applied. Apply when grain moisture is 35 percent or less. Corn should be physiologically mature (black layer formed) with maximum kernel fill complete. Apply at least 7 days before harvest.
  • Gramaxone or Parazone -  (paraquat) may be used for drying weeds in field corn, seed corn, and popcorn just be-fore harvest. Apply when corn is mature - after the black layer has formed at the base of the kernels.
Soybean - The same products are labeled as harvest aids for Soybean plus the herbicide Sharpen.
  • Aim - (carfentrazone) can be applied prior to harvest of mature soybeans for dessication of velvetleaf, morningglory, pigweeds, and other weeds. Apply at least 3 days before harvest.
  • Gramoxone and Parazone - (paraquat) may be used for drying weeds in soybeans just before harvest. For indeterminate soybean varieties, apply when 65 percent of the seed pods have reached a mature brown color or when seed moisture is 30 percent or less. For determinate varieties, apply when at least one-half of the leaves have dropped and the rest of the leaves are turning yellow.
  • Glyphosate - can be applied as a preharvest treatment to control perennial and annual weeds in soybeans. Dessication from glyphosate application is less rapid than that from Gramoxone.
  • Sharpen - (saflufenacil) can be applied broadcast at rates of 1 to 2 oz/A to soybeans that have reached physiological maturity. Indeterminate varieties should have greater than 65% brown pods and greater than 70% leaf drop with seed moisture of 30% or less. Determinate varieties should have greater than 50% leaf drop with the rest of the leaves yellowing.
If considering a pre-harvest herbicide application please read the label for additional information including harvest interval and annual product application restrictions.


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