Pulling the trigger on a foliar spray for thrips management for cotton can be a tough call to make. Some seasons, at-plant insecticides get cotton growers through the thrips window. But seasons can vary regionally and locally, and sometimes an in-season spray for thrips is needed.
Ron Smith is the retired Alabama Cooperative Extension Service cotton entomologist. Scott Graham is the current ACES cotton entomologist. In the recent ACES Cotton Team Cotton Shorts, they provided some things to consider when considering a foliar spray for thrips on cotton:
- When was the cotton planted? In general, earlier planted cotton tends to have higher thrips pressure than later planted cotton. Use the Thrips Model to monitor the expected thrips pressure on your farm.
- What is the weather like? The main reason for the point above is weather. Earlier planting dates tend to be much cooler (particularly at night) and cotton is not growing as fast. Thrips injury is largely dependent on how many thrips are in the field AND how well the cotton is growing. When the cotton is growing rapidly, it can ‘out-run’ thrips in many cases. In cooler conditions lower populations of thrips can do significant damage because the cotton simply isn’t growing.
- What at-plant insecticide was used? If a basic insecticide seed treatment (IST) was used, such as imidacloprid alone, a supplemental application may be needed. Premium ISTs (Aeris, Avicta Elite, BASF Prime) have at least two modes of action against thrips and typically provide slightly better control vs basic ISTs. Typically, in-furrow insecticides (liquid or granular) provide better control than ISTs. In particular, cotton treated with aldicarb (AgLogic) rarely requires supplemental foliar treatments. One thing to watch is weather. If conditions become cool and wet, there is potential to leach acephate out of the rootzone prior to plant up take. In these situations, a foliar spray is likely to be needed. My experience is that imidacloprid in-furrow performs better than acephate under these conditions.
If the amount of thrips injury does justify a spray, several options are available. You can read more about options available for thrips control here.