Chris Boerboom, Ext. Weed Scientist

 

Despite the late planting of many winter wheat fields, it appears that most wheat fields have come through the winter in good shape. However, wheat might be smaller than normal at this time of the year, which means the wheat might be more susceptible to weed competition. Consequently, it might be worthwhile to scout fields to see if a herbicide application is justified. If so, be sure to schedule or make the application soon for two reasons. First, wheat herbicides should be applied when the wheat is at its most tolerant stage. The two herbicides that generally have the greatest risk of injuring winter wheat are 2,4-D and dicamba (i.e. Banvel, Clarity). In particular, late applications of dicamba or 2,4-D can cause kernels to abort and leave blank heads (see image). In the case of the wheat in this image, a late application of 2,4-D plus dicamba caused most of the heads to be blank and the treated field yielded less than 20 bu/a. Dicamba must be applied before the jointing stage and dicamba has a maximum rate of 4 fluid oz/a. For 2,4-D, labels may allow applications until the early boot stage. However, we recommend applications before the jointing stage for greater crop safety and do not recommend later applications because of the risk of injury. 

 

Latest application stage for 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	before flag leaf shows
Harmony GT	before flag leaf shows
MCPA	before jointing
Starane	through flag leaf emergence
Stinger	before the boot stage
2,4-D	before jointing

 

A second reason to consider applications to wheat in the near future is to optimize weed control. Right now weeds are relatively small and are more sensitive to herbicides. Moderate herbicide rates, rather than maximum rates, can be used to get good control.  Considering that corn planting is right around the corner and corn herbicide applications will be starting soon, it is probably wise take care of the wheat before the season gets busy and the weeds get large.