Thrips migrated from wild hosts unusually late in 2019 and in extremely high numbers. The peak movement into cotton occurred from mid-May to early June. This late movement was likely the result of an extended May to June drought that caused wild host plants to dry down rapidly following abundant moisture going into the spring season.
In other words, a heavy buildup on wild hosts was followed by drought, which caused thrips to search for a better host. Seedling cotton was that host. Our later planted cotton encountered this heavy pressure and was at the most susceptible stage (1 to 5 true leaves) when the thrips migrated from wild hosts. Earlier planted cotton also had heavy thrips damage in some areas.
I visited earlier planted fields under extreme drought that received economic damage from thrips even at the 5th to 9th true leaf stage in 2019. Some fields required two or more foliar thrips sprays on top of an at-plant seed treatment.
Seed treatments or in-furrow sprays are still wise investments, even though they have lost some of their effectiveness against thrips due to resistance. Multiple foliar sprays with acephate can aggravate spider mites, especially under hot, dry conditions as occurred in 2019. In the future, I would not advise more than one foliar application of acephate on seedling cotton, and that application should be timed prior to the 2nd or 3rd true leaf.
Other options for foliar sprays that should be less likely to aggravate mites are Bidrin, dimethoate, and Radiant.
Some growers may want to consider going back to the granular insecticide aldicarb (sold under the trade name Ag-Logic) on some acreage in 2020. This may be especially true where nematodes or spider mites have been a limiting problem in recent years.
Aldicarb has always provided good to excellent control of spider mites. CNI (formerly ChemNut) has been the primary distributor for Ag-Logic in recent years, but it is my understanding that Helena will also be a supplier in 2020. The usage range for aldicarb on cotton in the past was 3 to 5 lbs of granules per acre.
When used in this range it should perform as good as or better than seed treatments, which would not be needed when using aldicarb. In talking with consultants in Georgia who have used this product in recent years, they have been pleased with the 4 or 5 pound rates. Three pounds is adequate, but if there is a mistake in calibration there is no margin for error.
AgFax Weed Solutions
The thrips prediction model, developed by entomologists at North Carolina State University with input from other southeastern cotton entomologists, was highly accurate in predicting the late thrips pressure in 2019 and will help us be more prepared for this pest in future years. This predictive model can be accessed on the web by going here.
To get a thrips prediction for your farm, just drop a pin on a location and give an expected planting date. The closer you are to the actual plant date, the more accurate this model is. Rather than selecting several field sites on a farm, I would access the model about once each week during the planting season for one location or field.
The model will obtain your local weather conditions from the nearest weather station. By knowing the local rainfall and temperatures, the model can predict how fast the wild hosts are drying down and the growing conditions for the seedling cotton.
This information may alert growers as to when a foliar overspray for thrips would be beneficial, even before the thrips damage and crinkled leaves are visible.