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Issue No. 20, Article 4/August 26, 2011

Preharvest Herbicide Applications in Corn and Soybean

The list of herbicide active ingredients available for preharvest applications in corn or soybean is relatively short. In corn, glyphosate, paraquat, and some formulations of 2,4-D or premixes containing 2,4-D may be applied to suppress/control weeds before harvest, while glyphosate, paraquat, dicamba (Clarity), and carfentrazone are labeled for preharvest applications in soybean. Be sure to consult product labels for specific application details. For example, not every formulation of 2,4-D is labeled for preharvest application in corn, and specific application intervals, rates, and restrictions can vary by product. See Table 1 for a compilation of general guidelines by product.

Table 1. General guidelines for preharvest herbicide applications in corn and soybean.

Product

Crop

Application rate

Application timing

Restrictions

Comments

2,4-D

Corn

1-2 pints/Aa

Apply after hard dough or dent.

Allow at least 7 days before harvest.

Consult the product label.

Rage D-Tech

Corn

Up to 31 fl oz/A

Apply after hard dough.

Allow at least 3 days before harvest.

Make only one preharvest application.

Glyphosateb

Corn: glyphosate-sensitive)

Ground: up to 64 fl oz/A
Aerial: up to 44 fl oz/A

Apply when grain moisture is 35% or less and the plant is physiologically mature.

Allow at least 7 days before harvest.

Not recommended for glyphosate-sensitive corn grown for seed.

 

Soybean: glyphosate-sensitive

Ground: up to 3.3 qt/A
Aerial: up to 44 fl oz/A

Apply after pods have lost all green color.

Allow at least 7 days before harvest.

Not recommended for glyphosate-sensitive soybean grown for seed.

 

Corn: glyphosate-resistant

Up to 22 fl oz/A

Apply when grain moisture is 35% or less and the plant is physiologically mature.

Allow at least 7 days before harvest.

Application allowed if combined total of previous applications does not exceed 1.54 lb ae glyphosate/acre.

 

Soybean: glyphosate-resistant

Up to 22 fl oz/A

Apply after pods have lost all green color.

Allow at least 14 days before harvest.

Will not control glyphosate-resistant waterhemp.

Gramoxone Inteon

Corn

1.2-2 pt/A

Apply after black layer.

Allow at least 7 days before harvest.

Make only one application.

 

Soybean

8-16 fl oz/A

Apply when at least 65% of pods are a mature brown color or when seed moisture is 30% or less.

Allow at least 15 days before harvest.

Do not graze or harvest for forage or hay.

Clarity

Soybean

8-32 fl oz/A

Apply after pods have reached a mature brown color and at least 75% leaf drop has occurred.

Allow at least 14 days before harvest.

Do not feed soybean fodder or hay.

Aim EW

Soybean

Up to 1.5 fl oz/A

Apply when crop is mature and grain has begun to dry down.

Allow at least 3 days before harvest

Can help defoliate or desic-cate velvetleaf, morning-glory, and pigweed.

aActual use rates can vary by product. Always consult the product label for information specific to that formulation.
bData taken from the Roundup WeatherMax label.

Preharvest herbicide applications should be made soon enough before harvest to allow sufficient time for dry-down of treated weeds. Dry-down of weed vegetation may be slowed during periods of cool and wet weather. All products labeled for these applications specify a period that must elapse between application and harvest, but additional time may be needed for dry-down of large weeds. Contact herbicides usually provide faster dry-down than translocated herbicides. Application practices that increase spray coverage of the target vegetation can improve control.

Also, be very cautious not to make a preharvest herbicide application before the crop development stage indicated on the product label. Applying herbicide before the stated interval may reduce crop seed production or viability.--Aaron Hager

Author:
Aaron Hager

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