KSU: Pre-harvest Weed Control in Wheat - Sharpen Update

July 11, 2019

The following article is by Dallas Peterson, Kansas State University extension weed specialist, and reprinted with permission from their Extension Agronomy eUpdate. It was recommended by Bob Klein, western Nebraska cropping systems extension specialist.

Last week’s eUpdate featured an article on pre-harvest weed control options in wheat, but did not include Sharpen in the table. Sharpen has been labelled and approved as a pre-harvest treatment in wheat in the U.S. for several years, but still does not have all the export approvals, including China. We made the decision, in conjunction with BASF, a few years ago to not include Sharpen in our recommendations as a pre-harvest treatment as some major wheat buyers at that time indicated they would not purchase wheat that had been treated with Sharpen. However, some additional markets have since been approved. If you want to use Sharpen as a pre-harvest treatment, it is important to visit with your grain buyer about whether they will accept wheat that has been treated with Sharpen. It has also has been brought to my attention that other herbicides labelled as pre-harvest treatments in wheat also may not have universal export approvals. Below is an updated table on pre-harvest treatments for wheat that includes Sharpen.

Product (rate/acre)	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. 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.
Sharpen (1 to 2 fl oz.)	Quick acting, usually within 3 days. Short waiting interval before harvest – 3 days.	Primarily effective on susceptible broadleaf weeds.	Apply when wheat is in the hard dough stage and grain contains less than 30% moisture. Apply with MSO and an ammonium-based adjuvant in a minimum spray volume of 10 gpa by ground or 5 gpa with aerial application. Consult grain buyer to see if they will accept Sharpen treated wheat because of export restrictions. Treated straw may be grazed or fed to livestock.
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.