Harvest Aids for Winter Wheat

Chris Boerboom, Extension Weed Scientist

I have received a couple calls concerning options to control large weeds in winter wheat fields to aid in harvest. First, Gramoxone or paraquat is not labeled as a harvest aid in wheat or other small grains. Options for harvest aid herbicides in winter wheat include glyphosate, 2,4-D, and dicamba.

Glyphosate can be applied to wheat and feed barley (no other small grains) to control grasses and suppress broadleaf weeds. Wheat must be in the hard dough stage (30% or less grain moisture) before treatment and wheat harvest must be delayed at least 7 days after application. Only 0.75 lb ae/a of glyphosate may be applied preharvest, which is equivalent to 32 oz/a of most generic glyphosate formulations, 22 oz/a of PowerMax and WeatherMax, and 24 oz/a of Touchdown Total as examples. It is not recommended to apply glyphosate preharvest to seed wheat because it may reduce seed germination.  

2.4-D ester should be more effective as a preharvest treatment than 2.4-D amine, but overall control of broadleaf weeds may be limited. Wheat must be in the hard dough stage before the application. Check the label of the 2,4-D product for allowable rates. Most labels have a maximum of 1 pt/a, but at least one lists a maximum of 2 pt/a. Most labels require a 14 day interval between application and harvest. 

Clarity (not other dicamba formulations) can be applied at 8 oz/a for broadleaf weed suppression. Wheat must be in the hard dough stage and the green color must be gone from the nodes in the stem. Wait 7 days before harvest after application.

As you can see, these preharvest herbicide options are rather limited. Consequently, it may be wise to consider these questions before making a preharvest herbicide application to winter wheat.

• Does the increased harvest efficiency outweigh the expense of the herbicide, application, and lost grain from sprayer tracks?

• If the weeds are mainly in patches, is there enough wheat in the weed patch to justify the expense of spraying the weeds and combining or would it be more logical to combine around the patches. This may be the case with weeds in areas where the wheat suffered winter damage or with large weeds like giant ragweed. 

• Will the herbicide provide enough control to desiccate the weeds before harvest? Often the herbicide label may not allow a high rate to control the large, mature weeds found in wheat fields.