As wheat harvest arrives in South Dakota, producers may be faced with problem areas in their fields where the weed control didn’t work as planned. These settings are candidates for pre-harvest herbicide applications. Treating them may help speed up harvest by drying the weeds down prior to combining. The non-selective herbicide options may also help in drying down the late maturing wheat heads that seem to be common with this years’ wide variation in plant development within fields.
There are several herbicides labeled for pre-harvest applications. They include Clarity, various glyphosate products, and several formulations of 2, 4-D Ester or Amine. Information on these products can be found in the 2013 South Dakota Crop Protection Guide Wheat. Check the individual labels for approved pre-harvest use.
Further information on pre-harvest herbicide treatments can be found in the SDSU Extension Harvest Aid Weed Control in Small Grain publication.
It is very important that anyone applying these herbicides on maturing wheat read and follow the label carefully for any restrictions or timing intervals that need to be observed. This is critical because misapplications can cause damage to the wheat seed. This may effect next year’s germination. So, any wheat intended for next year’s seed needs to be tested for proper germination prior to seeding.
Also watch out for neighboring fields and other sensitive areas. The herbicides listed above can volatilize and drift. Watch out particularly when using ester formulations and when temperatures are over 85° F.
The decision to apply a pre-harvest treatment must be weighed against the crop damage potential. South Dakota research showed the time of greatest yield risk when applying a dry down treatment is five to seven days before heading to seven to 10 days after heading. In addition to yield concerns North Dakota researchers have determined a link between pre-harvest treatments and poor end use quality.
Finally, it is critical to get the best control possible when spraying. Most of the weeds are going to be large and it will be important to use a full rate of herbicide and look at possible tank-mix options for the best control potential.