Weed management in wheat
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Herbicide selection for broadleaf weeds in winter wheat past Feeke’s Stage 6
Once wheat has passed Feeke’s Stage 6, the risk of herbicide injury from 2,4-D, MCPA, Banvel/Clarity, or Curtail increases and application of these herbicides is not recommended. In this situation, the remaining herbicide options for broadleaf weed control are Harmony Extra, Harmony GT, Express, Buctril, Stinger and Starane. Harmony Extra, Harmony GT, Affinity BroadSpec and Express can be applied to wheat until the flag leaf is visible (before Feeke’s Stage 8). Buctril, Stinger and Starane can be applied to wheat up to boot stage (before Feeke’s Stage 9).
Each spring there are questions about the risks associated with 2,4-D or MCPA application to wheat past Feeke’s Stage 6. Wheat tolerance of 2,4-D is highest between Feeke’s stages 3 and 6 and is lowest in Feeke’s Stages 9 and 10. Between stages 6 and 9, sensitivity to 2,4-D gradually increases as wheat growth stage advances. Thus, the risk of injury increases as wheat growth stage advances between stages 6 and 9. Severe injury is highly probable when 2,4-D is applied at Feeke’s stages 9 and 10.
MSU recommends that application of 2,4-D to wheat be made after wheat has reached Feeke’s stage 3 but prior to Feeke’s stage 6. If growers choose to apply 2,4-D at later stages, they need to understand the associated risk. This risk can be minimized by applying the amine form of 2,4-D or reducing the rate of a 2,4-D ester. A much better alternative on wheat past Feeke’s stage 6 is to use another broadleaf herbicide with a wider application window that is effective on the weeds present in the field.
Herbicide selection for grass weeds in winter wheat
Several growers have reported problems with grasses such as cheatgrass, windgrass and annual bluegrass in their winter wheat. The control options for grass control in winter wheat is limited. Osprey, Olympus 70% and Everest are products labeled for use in Michigan up to the jointing stage; however, special attention needs to be made to the rotational restrictions found on their labels. The weeds controlled by these products will vary, so proper identification of the problematic species is important. The lengthy rotation restrictions associated with these products will restrict the rotation options for growers. Of the three products mentioned, Osprey has the shortest rotation restrictions for most crops grown in Michigan. MSU currently has limited experience with these products and cannot advise farmers on how they will perform in Michigan. Farmers should be advised to read and understand the information found on the label. Windgrass control can also be achieved using Puma. More information about Puma’s use in winter wheat can be found in the 2006 Weed Control Guide for Field Crops, E-434 (page 86).
Herbicide carrier selection
Liquid urea-ammonium nitrate fertilizer (28%N) is a common carrier for herbicides in wheat. The most common herbicide to be used in this manner is 2,4-D ester (2,4-D amine is difficult to mix in 28% N). Application of herbicide in 28% liquid nitrogen can cause leaf burn from the nitrogen, especially under hot, humid conditions. This risk increases with later wheat growth stages because more leaf area is exposed to the treatment and recovery time is shorter. In addition, the use of surfactant (required with herbicides such as Harmony Extra) greatly increases leaf burn potential. MSU research has demonstrated that excessive leaf burn from high nitrogen rates combined with surfactant can reduce wheat yield. To minimize this risk:
- Do not apply more than 20 lbs of nitrogen per acre in the form of 28% N when using a surfactant with herbicide.
- Do not apply more than 40 lbs of nitrogen per acre in the form of 28 % N when no surfactant is used.
- Avoid high-temperature, high-humidity days. Late afternoon applications carry less risk of leaf burn.