Josh Copes, Stephenson, Daniel O., Miller, Donnie K. | 2/5/2018 3:11:08 PM
After harvest, and particularly when it is dry, questions arise concerning fall burndown applications that contain residual herbicides. As with any field operation, fall burndown should provide a monetary benefit as preparing fields for the following year requires time and money. Producers should realize that some fall-applied residual herbicides will provide control of most winter annuals, which may result in excess soil and bed erosion. If this is the case, why apply a fall burndown? When glyphosate-resistant Italian ryegrass and some other winter annual weeds like henbit are an issue, research has shown that a fall residual herbicide application will provide good to excellent control of these species into the following spring. The table below is a glyphosate-resistant Italian ryegrass weed control program developed by Mississippi State University weed scientists that LSU AgCenter weed scientists have adopted. The fall-applied herbicides listed in the table will provide some control of henbit as well.
To combat glyphosate-resistant Italian ryegrass, many producers tank-mix Select Max (clethodim) in their spring burndown. Unfortunately, Italian ryegrass control failures following Select Max (clethodim) applications have occurred in Louisiana. If controlling Italian ryegrass has been an issue, and control failures with clethodim have occurred, one of the fall programs in the Table 1 should be utilized.
Regardless of the upcoming spring crop, LSU AgCenter specialists suggest applying a spring burndown four to six weeks prior to planting. This gives plenty of time for weeds to die and break the “green bridge.” Soil residual herbicides, if applied, will keep the fields weed free until planting. If the upcoming crop is corn, a soil residual herbicide applied in the fall may provide adequate weed control until planting. Fall residual herbicides can keep the field weed-free until planting. However, if planting soybeans or cotton, a fall-applied soil residual herbicide may not be the best choice. In some years soil residual herbicides can provide weed control up to 120 days. If applied in early December, expect adequate weed control until mid-to-late March. It is a mistake to assume that if a residual herbicide is applied in December, then spring burndown can be skipped. Fields must be scouted.
When applying burndown to fields near planting, herbicide selection, rate and spray coverage are very important to ensure complete control. If marestail, henbit, cutleaf evening-primrose and sowthistle are present, be sure to apply 2,4-D at 1 lb. of acid equivalent per acre. In many instances when weed control is unsatisfactory from spring burndown, it is because 2,4-D rates were too low or 2,4-D was not applied at all.
The main goal of any burndown operation is to be weed-free at the time of planting. Choice of fall or spring burndown will depend on the intended crop, presence of Italian ryegrass and the likelihood of soil and bed erosion. Finally, economics should be an important consideration when choosing burndown programs.