By Christy Sprague
The colder than normal spring and wet weather has made it difficult to spray winter wheat this year for weeds. While we normally would have all of our wheat herbicides applied by now, there are still several fields that haven't been sprayed. However, winter wheat has continued to develop and many fields have reached jointing, or Feeke’s growth stage 6. Below 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. These herbicides include 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, or 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. The herbicides 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.
Other herbicides that should be applied prior to Feeke’s stage 6 are Osprey, PowerFlex HL and Puma. These herbicides are some of our best options for control of grasses in winter wheat including common windgrass. Osprey and PowerFlex are also our best options for control of annual bluegrass. Again, these herbicides should not be applied after winter wheat has started to joint.
Some herbicides, including Affinity BroadSpec, Harmony Extra, Harmony and Express, do not have the same restrictions as several of the one previously mentioned. These 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. These herbicides also have better control of common chickweed than many of the growth regulator herbicides. Peak is also an option for common chickweed control; however, longer rotation restrictions of 22 months on many crops including soybeans often restrict the use of this herbicide.
One 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, such as 2,4-D and dicamba. The application window for Huskie is from 1-leaf wheat up to flag leaf emergence, or 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, or 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 common windgrass, can be found in Chapter 3 of the “2014 Weed Control Guide for Field Crops,” Michigan State University Extension bulletin E-434.