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Corn Growth Stage and Post-Emergence Herbicides

by Aaron Hager, Extension Weed Scientist
University of Illinois

The labels of most post-emergence corn herbicides allow applications at various crop growth stages, but almost all product labels indicate a maximum growth stage beyond which broadcast applications should not be made, and a few even state a minimum growth stage before which applications should not be made.

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These growth stages are usually indicated as a particular plant height or leaf stage; sometimes both of these are listed. For product labels that indicate a specific corn height and growth state, be sure to follow the more restrictive of the two. Application restrictions exist for several reasons, but of particular importance is the increased likelihood of crop injury if applications are made outside a specified growth stage or range. The following table lists the maximum corn growth stage for broadcast application of several post-emergence corn herbicides. Be sure to consult the respective product label for additional precautions or restrictions.

How to Properly Use Dicamba on Soybeans

read farmdocdaily article

As the growing season approaches it is important for farmers to understand how to use dicamba on resistant soybean varieties. Todd Gleason has more with University of Illinois weed scientist Aaron Hager.



The following is an excerpt from the March 23 farmdocdaily article posted by University of Illinois Weed Scientist Aaron Hager.

Steps for Successful Weed Management in Dicamba-Resistant Soybean

Step 1
  • plant dicamba soybean seed into a weed-free seedbed
  • achieve a weed-free seedbed through the use of preplant tillage, an effective burndown herbicide(s), or a combination of tillage and burndown herbicides
Step 2:
  • select and apply within 7 days of planting a soil-residual herbicide that targets your most problematic weed species; if desired (and labeled), add dicamba and an appropriate buffer
  • for waterhemp or Palmer amaranth, select a product containing the active ingredients from one of the following categories of control:
Excellent Good Acceptable
sulfentrazone pyroxasulfone     S-metolachlor/metolachlor
flumioxazin metribuzin acetochlor
fomesafen+metolachlor     dimethenamid pendimethalin
  • Excellent: greatest efficacy on Amaranthus species and longest residual control
  • Good: good efficacy on Amaranthus species, residual control generally not as long
  • Acceptable: stronger on grass species but with some activity on Amaranthus species
Step 3:
  • scout fields 14 days after planting, apply dicamba at 0.5 lb ae/acre when weeds are less than 3 inches tall and when conditions allow for the application, consider adding an approved soil-residual herbicide to the tank mix
Step 4:
  • scout treated fields 7 days after the dicamba application; if control is not complete or another flush of weeds has emerged, consider using non-dicamba options for complete control; examples include alternative herbicides, cultivation, and hand rogueing; the goal should be zero weed seed production