Every year, peanut growers question if they should spray for thrips in peanut. Mississippi State University Extension recommends using an at-planting insecticide to manage thrips. Normally, that approach is adequate in most situations, say Jeff Gore, Research and Extension Entomologist and Jason Sarver, Extension Peanut Specialist.
Research and Extension Entomologist and Jason Sarver, Extension Peanut Specialist - See more at: http://www.mississippi-crops.com/2016/05/20/thrips-in-peanut-when-to-spr...
Two years ago, they did a study two years ago where they sprayed peanuts one, two, three or four times at weekly intervals after emergence. The results are shown in this figure.

There was an increase in peanut yields with each subsequent application for thrips. Yields ranged from about 5,000 pounds per acre in the untreated to about 5,800 pounds for four applications. This would suggest that spraying thrips in peanut will provide significant economic benefits for growers.

However, one key is that the peanuts in this study got a substantial amount of rain at emergence that resulted in heavy herbicide injury. The researchers did more studies in 2015 that are being repeated this year to simulate this same scenario. The results are similar to the data shown above.

The overall conclusion from these studies is that significant benefits from thrips sprays in peanuts can be seen when the plants are under some type of stress. The stress can come from herbicide injury, extremely dry conditions, extremely wet conditions, cooler temperatures, or any other factor that can slow peanut growth.

In general, thrips populations appear to be very high this year across the state. In general, at-planting insecticides should provide adequate control as long as the peanuts are growing normally. However, when peanuts are under stress and thrips are causing additional stress, sprays may be justified even where an at-planting insecticide was used.

This is especially true given the cooler temperatures we have had this spring. It is important to remember that the clock starts ticking on the longevity of at-planting insecticides as soon as they go in the ground, not when the peanuts emerge. The insecticides will work better if the peanuts emerge within a week than if it takes 2 weeks for the peanuts to emerge.

The key is to minimize the stresses that you can control when multiple stresses occur on seedling peanuts.