Preemergence Herbicide Treatments Behind the Cotton Planter

–

Dr. Steve Li, Auburn Weed Scientist

–

Cotton planting will be in full swing in just another week or two. One thing that I cannot emphasize enough is to START CLEAN (free of weeds), particularly in no-till fields. A single-pass burndown treatment is often not enough. It is hard to kill everything in no-till fields with a single burndown treatment, particularly when weeds are tall and thick. A second-pass pre-plant burndown treatment, or a follow-up application of Gramoxone with soil herbicides behind the planter is needed to START CLEAN. Otherwise, some weeds that “appear to be dead” may recover and regrow. Sometimes burndown treatments only injure foliage and the readily visible plant canopy (leaving growing points, crowns, and roots alive); resulting in weeds that fully recover in a few days to exert competition to the crop.

I recommend using two-way mixes as PRE treatments. They provide both a broader weed control spectrum and longer duration control. A few effective treatments I’ve evaluated in recent years include:

1. Reflex + Cotoran (best treatment on broadleaf weeds such as sicklepod, morning glory, teaweed and pigweed)
2. Reflex + Warrant* (best treatment on annual grasses and pigweed)
3. Reflex + Brake (best treatment on pigweed)
4. Cotoran + Warrant* (best treatment on heavy soils where Reflex does not fit well)
5. Cotoran + Brake (best treatment for pigweed and broadleaf weeds on heavy textured soils).
   • *Application of Warrant herbicide is legal in Florida, but it cannot be sold in Florida

Use rates for these herbicides in two-way mixes on sandy loam soils are: Reflex 8-10 oz/A, Cotoran 1 pt/A, Warrant 2 pt/A, Brake 16 oz/A. Rates for these herbicides in two-way mixes on silt loam soils are: Reflex 10 oz/A, Cotoran 1.5 pt/A, Warrant 2.5 pt/A, Brake 20 oz/A. Rainfall or irrigation within 3-4 days after application is needed to properly activate these herbicides.

If you run into a dry spell in May and there is no chance of rain in the next 7-10 days after planting, one alternative is to apply PRE-treatments over smooth, prepared seed beds prior to planting … just ahead of rain that will eventually come. The purpose is to get herbicides activated by rainfall, then utilize the moisture to get a crop stand after the rain. A pass by a strip-till may facilitate cotton emergence by breaking any crust layer at the soil surface caused by heavy rain and reduce herbicide injury.