When selecting a herbicide for winter wheat, the first step is finding a herbicide that has good activity on the target weeds. Of course, the herbicide labels should be checked for the weeds controlled, but a quick short cut to identifying potential herbicides is to check our rating table in the Pest Management in Wisconsin Field Crops bulletin. The control ratings for broadleaf weeds with common small grain herbicides are listed on page 182. (If you do not have the bulletin, but have a fast internet connection, the bulletin is available online at http://learningstore.uwex.edu/Pest-Management-in-Wisconsin-Field-Crops2008-P155C0.aspx or a copy can be ordered from this site).

For three common wheat herbicides, here are some good rules of thumb to keep in mind about their activity.

    2,4-D:  good on the mustard family, but weak on wild buckwheat and smartweeds.
    Dicamba (Banvel, Clarity):  good on wild buckwheat and smartweeds, but generally weaker on the mustard family; higher risk of injury and the rate is limited to 4 oz/a on wheat.
    Sulfonylurea herbicides (Harmony Extra, Harmony GT, Affinity BroadSpec):  generally excellent on the mustard family.

The second step in a good weed management program is proper application timing and winter wheat is no exception. In fact, proper timing may be more critical to protect wheat from injury than in corn or soybeans. The maximum growth stage when herbicides should be applied should be closely followed (Table 1).  In particular, late applications of dicamba or 2,4-D can cause kernels to abort and leave blank heads.  Dicamba must be applied before the jointing stage.  For 2,4-D, labels may allow applications until the early boot stage.  However, we recommend applications before the jointing stage and do not recommend later applications because of the risk of injury.  Overall, most herbicides should be applied by the jointing stage to get the best weed control and this will also protect the wheat from injury.   

Table 1. Application timings of common winter wheat herbicides for broadleaf weeds
        

Affinity BroadSpec	before flag leaf shows
Aim	before jointing stage
Dicamba	before jointing stage
Buctril	before boot stage
Harmony Extra SG	before flag leaf shows
Harmony SG	before flag leaf shows
Huskie	before flag leaf shows
MCPA	before jointing
Rage D-Tech	before jointing
Starane	through flag leaf emergence
Stinger	before the boot stage
2,4-D	before jointing

A few notes are worth mentioning on new wheat herbicides or new formulations. One new herbicide for 2008 is Huskie from Bayer. Huskie is a premix of pyrasulfotole + bromoxynil + a safener. Pyrasulfotole is a new herbicide ingredient, but it is in the same family as the bleaching herbicides of Callisto and Laudis. Bromoxynil is the ingredient in Buctril. Huskie would typically be applied at 11 oz/a along with either 0.5-1 lb/a ammonium sulfate or 1-2 qt/a 28% nitrogen.  Huskie will control many annual broadleaf weeds and they should be sprayed before they have more than 4 to 6 leaves. Other weed scientists have reported that wheat has good tolerance to Huskie. If the timings fertilizing and weed control are similar, Huskie can be applied using nitrogen fertilizer as the carrier instead of water.

Rage D-Tech from FMC is another new premixed herbicide that can be used on wheat. Rage D-Tech is a mixture of 2,4-D and the herbicide in Aim (carfentrazone) and can be applied at rates from 8 to 16 oz/a. The 8 oz/a rate would give the equivalent to 8.3 oz/a 2,4-D LV4 plus 0.5 oz/a Aim. Rage D-Tech needs the addition of 0.25% surfactant and will control many broadleaf weeds when sprayed before 4 to 6 inches tall. Wheat should be sprayed before jointing because of the 2,4-D component. Rage D-Tech may speckle the wheat leaves because of the Aim component, but this should not be a concern unless the leaves are wet from dew or rain.  

 

DuPont has changed two of their wheat herbicide formulations. Harmony SG is the new version of Harmony GT and Harmony Extra SG is the new version of Harmony Extra XP. The new “SG” stands for soluble granules. While these are new formulations, the more important change is that the herbicide concentrations have changed. Both new formulations are less concentrated so labeled rates are 50% higher than with the old formulations. If you are using either of these herbicides, be sure to check which version you are spraying and double check the rates.