Herbicide injury and weed control are both challenging when dusting in cotton and the topic deserves discussion.
The most effective approach to minimize cotton injury from preemergence (PRE) herbicides is to place the cotton seed in moist soil where it can imbibe (absorb) clean water free of herbicides. Next we need our cotton roots to “out run” the herbicide as the herbicide is moving down into the soil with rainfall or irrigation.
When placing cotton seed in dry soil and then applying a PRE herbicide, it is likely impossible for water to get to the seed without being contaminated with the herbicide. However no two herbicides pose the same challenge under these conditions; here are a few thoughts with several products:
1. Reflex moves very effectively in water thus it is the product most likely to reach the seed at higher concentrations. Although that is not beneficial for the cotton seed, it is very beneficial for weed control as the product is activated more effectively with lower amounts of rainfall or irrigation than other cotton herbicides. Additionally, our research has shown Reflex to sit on the soil for 17 days before being activated and then still providing about 90% control of the pigweed emerging after activation.
2. Warrant poses a unique challenge, if the encapsulation breaks down releasing the active ingredient prior the cotton plant emerging then injury can be quite significant. It is the encapsulation of Warrant that provides us the ability to use it “safely” PRE in cotton. Any time one is uncertain of cotton emergence within 5 or 6 days of applying Warrant, one may want to consider other options. Ideally Warrant needs around a half inch of rain for activation and our research has shown it to still be quite effective on pigweed after sitting on the soil and waiting 11 days for activation.
3. Diuron will move down to the seed less aggressively than Reflex but if a heavy rain occurs within a few days of dusting the cotton in and applying diuron, injury will be much greater than normal.
4. Brake likely poses the least damage potential to cotton in this environment but the herbicide may not perform on weeds properly until a half inch or more of rainfall occurs.
AgFax Weed Solutions
Obviously, dusting cotton in and applying PRE herbicides is far from ideal. The next thought from every grower is, of course, I just want apply herbicides after planting. This thought is extremely scary when considering the monumental challenges our family farms face with herbicide resistance in Palmer amaranth. If one does follow this path of not using PRE herbicides, there are several key points to consider.
First, there must be no weeds emerged when the cotton seed is placed in dry soil. In theory, no additional weeds should emerge until it rains.
Second, the first postemergence herbicide application should occur as soon as the cotton is fully emerged (do not wait to see weeds at 70 mph from the road); the treatment must kill emerged weeds (Palmer and spiderwort) and must include residual herbicides.
Third, a second postemergence herbicide application should be made 14 to 18 days later and again include a residual product.
And finally, and absolutely essential, is that the layby application is made with hoods or a layby rig improving weed coverage and control while minimizing cotton injury. The layby application should include conventional herbicide chemistry such as diuron, Caparol or Cotoran; also include Envoke if help is needed with morningglory or nutsedge.