By Dallas Peterson and Curtis Thompson, Extension Weed Management Specialists
'Sometimes a single early preplant burndown treatment prior to planting wheat does not hold down grass and broadleaf weed pressure all the way until the time wheat is planted. In some areas of Kansas this year, higher-than-normal rainfall in August and September has led to a flush of grasses, volunteer wheat, and broadleaf weeds on some fields that had received an earlier burndown treatment.
When this occurs, producers may want to add another herbicide to glyphosate for additional broadleaf weed control in the second burndown treatment closer to the time of wheat planting. Is 2,4-D a good option for tankmixing with glyphosate in this situation?
The label for 2,4-D LV, which is the best form of 2,4-D to use in this case, is a little vague about the required waiting time between application on fallow or stubble ground and the planting of wheat. When used on fallow ground or crop stubble, the label states you can plant only those crops listed on the label within 29 days after application of 2,4-D LV4. Wheat is one of the crops listed on the label, so that’s fine. Corn and soybeans have specific guidelines for preplant application on the label, but small grains and sorghum do not.
The label also states that wheat and other crops listed on the label may be at risk of crop injury or loss if planted soon after application, especially during the first 14 days. The risk of injury to wheat following a 2,4-D application to fallow or crop stubble increases: (1) at higher use rates, (2) if soil temperatures have been cold, or (3) if soils have been excessively wet or dry in the days following application. All of these factors affect the degradation of 2,4-D LV4 after application. In practice, the risk of injury is probably minimal if you allow a 7-day waiting interval between application of up to 1 pt/acre of 2,4-D LV4 and planting wheat.
The greatest risk of crop injury to wheat would occur with 2,4-D application close to planting and a good rainfall shortly after planting.