Pre-harvest weed control in wheat

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Once again it appears that weeds are going to cause harvest problems in wheat. Thin stands from winterkill in some areas and the abundant rains in May and June have resulted in weeds showing up in many wheat fields, especially if not treated earlier. No one wants to spend extra money on a below-average crop, but these weeds can make harvest very difficult.

Unfortunately, there aren’t many good options at this point in time. There are also a lot of questions about which herbicides are approved and the “use guidelines and restrictions” for pre-harvest treatments in wheat. Listed 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.

Sharpen is now labeled for use as a pre-harvest treatment in wheat and is approved in North America, but is not included in the table because it does not have Maximum Residue Limit (MRL) approvals for use as a pre-harvest wheat treatment in some key export markets. Some grain marketers have indicated they will not accept wheat that was treated with a pre-harvest application of Sharpen, so it is not being promoted for that use at this point in time.

Please note that the 2,4-D rate approved for pre-harvest weed control in wheat has been reduced to a maximum of 0.5 lb/acre, which is equal to 1 pt of a 4-lb formulation or 2/3 pt of a 6-lb material. 2,4-D also has a 14-day pre-harvest requirement. 

Another herbicide that is sometimes mentioned as a possible pre-harvest treatment is paraquat. Paraquat is not labeled for pre-harvest 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. 




Product and rate




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.

High potential for spray drift to susceptible crops.

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 qt  of 3 lb ae/gal product, or 22 fl oz of Roundup PowerMax or WeatherMax)

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.  Kochia, pigweeds, and marestail may be resistant.

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.  Kochia, pigweeds, and marestail may be resistant.

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 (1 pt of 4lb/gal product or 2/3 pt 6 lb/gal product)

Provides control of susceptible broadleaf weeds.

Acts slowly. Weak on kochia and wild buckwheat.

Cannot harvest grain until 14 days after application.

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