By Christy Sprague
Unseasonably warm temperatures experienced earlier this month have increased the growth of Michigan's winter wheat crop. Because of these temperatures, we are seeing a wide range of wheat growth stages across Michigan. In fact, several wheat fields have reached or are approaching jointing (Feeke's stage 6), which needs to be considered when choosing herbicides for weed control. Achieving good herbicide coverage may also be tougher because of early rapid wheat growth. While some of Michigan's wheat crop has already been sprayed for weed control, here are some considerations for fields that have not yet been treated.
Weed control options need to be based on what weeds are in the field and, more importantly, the stage of winter wheat growth. If herbicides are applied after these maximum stages, late herbicide applications can lead to excessive herbicide injury that can cause kernel abortion and blank wheat heads, ultimately reducing yield. Some of the more restrictive herbicides that can be used in winter wheat are the plant growth regulator herbicides including 2,4-D amine, 2,4-D ester, dicamba (Banvel or Clarity), MCPA, and Curtail (2,4-D amine + Stinger). All plant growth regulator herbicides need to be applied prior to winter wheat jointing (Feeke's stage 6). If winter wheat is at jointing, these herbicides should no longer be used.
The plant growth regulator herbicides are typically good on summer annual weeds like common lambsquarters, pigweed, and common ragweed, but vary in their control of some of the more common winter annual weeds like common chickweed. 2,4-D, MCPA, and Curtail will not control chickweed. With the warmer weather conditions, it is important to scout fields and make sure that wheat has not exceeded the maximum growth stages in which these herbicides may be applied.
Herbicides including Affinity BroadSpec, Harmony Extra, Harmony, and Express do not have the same restrictions as many of the plant growth regulator herbicides. These herbicides can be applied when the wheat is at the 2-leaf stage (Feeke's stage 1.2) to just before the flag-leaf is visible (Feeke's stage 7.9). All of these herbicides also have better control of common chickweed than many of the growth regulator herbicides. Peak, another herbicide, is also an option for common chickweed control. However, longer rotation restrictions (22 months) to many crops including soybean often restrict the use of this herbicide.
Another herbicide that will provide good control of common chickweed and has activity on some of our common winter annual weeds is the herbicide Huskie. Huskie also has a longer application window than the plant growth regulator herbicides (e.g, 2,4-D and dicamba). The application window for Huskie is from 1-leaf wheat up to flag leaf emergence (Feeke's stage 1 to 7.9).
Buctril, Stinger, Starane, and Widematch (Stinger + Starane) are other herbicides that will control broadleaf weeds in winter wheat. These herbicides have the longest application window. They can all be applied to winter wheat up to the boot stage (Feeke's stage 9). However, many of these herbicides have fairly narrow spectrums of weed control. Buctril provides better control of summer annual weeds and is not very effective against winter annuals. Starane has a very narrow weed control spectrum, but is excellent in controlling hemp dogbane. Stinger, on the other hand, provides excellent Canada thistle control.
More information for control of winter and summer annual weeds including hard-to-control grasses, like annual bluegrass, cheat, and windgrass, can be found in Chapter 3 of the "MSU 2012 Weed Control Guide for Field Crops" (E-434).
This article was published on MSU Extension News. For more information from MSU Extension, visit http://news.msue.msu.edu. To contact an expert in your area, visit http://expert.msue.msu.edu, or call 888-MSUE4MI (888-678-3464).
Sprague is a professor at Michigan State University Extension, Department of Crop and Soil Sciences