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Department of Agronomy

Kansas State University

1712 Claflin Rd.

2004 Throckmorton PSC

Manhatan, KS 66506

785-532-6101

agronomy@ksu.edu

Extension Agronomy

Special Edition: Preharvest weed control in wheat - Reminder

Late-season weeds in wheat continue to be a problem in many parts of Kansas as a result of the thin wheat crop and continued wet weather. No one wants to spend extra money on a below-average crop, but these weeds can make harvest very difficult. However, there continues to be a lot of questions about which herbicides are approved and the use guidelines and restrictions for preharvest treatments in wheat. 

One herbicide that is sometimes mentioned as a preharvest treatment is paraquat. Paraquat is not labeled for preharvest treatment in wheat. Application of paraquat to wheat is an illegal treatment and can result in a quarantine and destruction of the harvested grain, along with severe fines. 

Below are the various herbicide options producers can use as pre-harvest aids in wheat. There are differences in how quickly they act to control the weeds, the interval requirement between application and grain harvest, and the level or length of control achieved. All of them will require good thorough spray coverage to be most effective.

 

 

Product and rate

Advantages

Disadvantages

Comments

Aim EC (1 to 2 oz)

Acts quickly, usually within 3 days.

Short waiting interval before harvest – 3 days.

Controls only broadleaf weeds.

Regrowth of weeds may occur after 2-3 weeks or more, depending on the rate used.

Apply after wheat is mature. Always apply with 1% v/v crop oil concentrate in a minimum spray volume of 5 gal/acre for aerial application and 10 gal/acre for ground applications.

Do not apply more than 2 oz of Aim during the growing season.

Dicamba (0.5 pt)

Controls many broadleaf weeds.  

A waiting period of 7 days is required before harvest.

Acts slowly to kill the weeds.

Controls only broadleaf weeds.

Apply when the wheat is in the hard dough stage and green color is gone from the nodes of the stem.

Do not use treated wheat for seed unless a germination test results in 95% or greater seed germination.

Glyphosate (1 to 2 pt of 3 lb ae/gal product)

Provides control of both grasses and susceptible broadleaf weeds.

Acts slowly. May take up to 2 weeks to completely kill weeds and grasses.

Cannot harvest grain until 7 days after application.

Apply when wheat is in the hard dough stage (30% or less grain moisture).

Consult label for recommended adjuvants.

Not recommended for wheat being harvested for use as seed.

Metsulfuron (0.1 oz)

Provides control of susceptible broadleaf weeds.

Acts slowly.

Cannot harvest grain until 10 days after application.

Controls only susceptible broadleaf weeds.

Apply when wheat is in the dough stage.

Always apply with a nonionic surfactant at 0.25 to 0.5% v/v.

Generally recommended in combination with glyphosate or 2,4-D.

Do not use on soils with a pH greater than 7.9.

Weeds growing under limited moisture may not be controlled.

Do not use treated straw for livestock feed.

2,4-D LVE (0.67 to 1 qt of 4lb/gal product)

Provides control of susceptible broadleaf weeds.

Acts slowly. Weak on kochia and wild buckwheat.

Most products have a 14 day preharvest requirement.

Apply when wheat is in the hard dough stage to control large, actively growing broadleaf weeds.

Weeds under drought stress may not be controlled.

Do not use treated straw for livestock feed.

 

Dallas Peterson, Weed Management Specialist
dpeterso@ksu.edu