With many parts of Louisiana experiencing significant rainfall events in the past week and corn planting in full swing, some insecticide seed treatments may have been adversely affected by the excess moisture. Insecticide seed treatments (ISTs) are neonicotinoid based insecticides that coat the outer layer of the seed offering protection from below and above ground early season insect pests. The systemic nature of ISTs make these compounds water soluble and facilitate the vascular movement of the insecticide into the plant tissue. Adequate moisture is required to move the insecticide into the root zone and available for plant uptake.
However, excess moisture may move the insecticide out of the root zone. Of the three neonicotinoid insecticides available for use on corn seed, thiamethoxam is the most water soluble at 4.1 g/l of water, followed by imidacloprid and clothianidin at 0.5 and 0.33 g/l, respectively. These values represent the degree of leachability but are highly dependent on soil type. Movement below and around the root zone may increase below ground control of insects such as wireworms, rootworms, and sugarcane beetles ; however, the dilution may limit root uptake and the amount of above ground protection offered. This can leave plants more susceptible to injury from chinch bugs, false chinch bugs, stink bugs and bill bugs.
Under ideal conditions, corn ISTs will give 14 to 18 days of protection from above ground pests. Fields under excess moisture, for extended periods of time, should be scouted routinely for damage after emergence. If immature and adult insects, such as chinch bugs, are found to be feeding on early corn it is often a sign that the IST may have lost its efficacy.
For more information or if you have any questions or concerns please contact Sebe Brown, or Drs. David Kerns or Julien Beuzelin.
Sebe Brown Cell: 318-498-1283 Office: 318-435-2903
Dr. David Kerns Cell: 318-439-4844 Office: 318-435-2157
Dr. Julien Beuzelin Cell: 337-501-7087 Office: 318-473-6523