Sometimes knowing if a supplemental foliar spray for thrips management is needed can be tricky. Some years an at-plant insecticide can get us through the thrips window (≈5-6th true leaf) but other years they may not. Things to consider are:
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 fast, 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. Attached below is some data from a trial we did in Madison Co. last year. Keep in mind the threshold for thrips injury (yellow line) is 3 (see rating scale).