Applying residual herbicides to prepared cotton beds in the fall, when time is more readily available and weather is cooperative, may save time and money in the spring.
If the fall burndown application results in the field being clean at planting, there is no need for a spring burndown application.
Ken Smith, Extension Weed Scientist with the Southeast Research and Extension Center, Monticello, Ark., examined four fall burndown treatments last fall to determine which ones could provide a clean field at planting.
The four alternatives included Valor at 2 ounces per acre, Reflex at 32 ounces per acre, Goal at 24 ounces per acre, and Envoke at 0.15 ounce per acre. He also had an untreated check.
Weeds observed throughout the winter and spring consisted of chickweed, poa, and henbit.
Weed control ratings were taken on four occasions; Jan. 8, Feb. 27, March 17, and May 12.
On Jan. 8 all four treatments were providing 97.5 percent to 100 percent control of all three weeds with one exception. Reflex was not controlling the chickweed.
By Feb. 27, the control of chickweed in the Goal plots had slipped to 89 percent, and poa control in the Reflex plots was slipping.
On March 17, poa control in the Envoke plots and chickweed control in the Goal plots was slipping.
Finally, on May 12, weed control in the Valor plots had slipped to 83.8 percent and 37.5 percent for chickweed and poa, respectively.
In the Envoke plots, weed control had slipped to 68.8 percent for both chickweed and poa. Goal's control of poa and chickweed was 84 percent and 79 percent respectively. Reflex was providing only 25 percent control of both poa and chickweed.
None of the fall burndown treatments were still giving greater than 90 percent control of all the weeds by May 12. A spring burndown application would be necessary to achieve a clean field at planting.
Six spring burndown alternatives were superimposed on the fall burndown treatments. The least expensive combinations are displayed in accompanying table.
The cheapest way to be clean at planting in this experiment was a total spring burndown program at a cost of $17.65 per acre. For $2 per acre more we achieved a clean field all winter and at planting by applying Valor in the fall and glyphosate in the spring.
Our Reflex burndown treatment was expensive and had to be followed with a good spring burndown to achieve good control on May 12.
The Goal and Envoke fall burndowns required a $26 or $27 per acre program, which included a spring burndown.