Cotton planting and early season thrips management are almost upon us. We are fortunate today to have varieties that have three-plus bale yield potential. While we can’t control rainfall patterns for 2020, we can make sure that other factors such as early season insects, especially thrips, do not stunt or delay growth and development of seedling cotton.
Seed treatments alone are not as effective as in-furrow granular insecticides used in the past. Because the seed treatments imidacloprid (Gaucho) and thiamethoxam (Cruiser) have lost some or much of their effectiveness due to insect resistance, we are forced to add additional thrips-suppressing measures such as in-furrow or foliar sprays in our management programs. Research has shown that foliar thrips sprays are most effective when applied at the 1st true leaf stage or very shortly thereafter. Such treatments on early planted cotton may be needed before growers finish planting later fields. Furthermore, an initial, timely spray may be most beneficial even before the 1st true leaf has visible thrips injury.
We now have a tool that helps us know when this first foliar spray may be most effective. This tool is a Thrips Prediction Model. It is quite accurate in forecasting thrips pressure based on planting date and local weather. The model can be accessed at climate.ncsu.edu/cottonTIP. To indicate your farm location, scroll across the map to your site and click to drop a red pin. You then select anticipated planting date. The model accesses nearest weather station information for temperature and rainfall, data which enable predictions about the growth of seedling cotton as well as the status of wild hosts that serve as sources for thrips migration.
We have determined that thrips migration from adjoining hosts can peak early, mid, or late in the planting window. Since weather is a big factor in both seedling growth and the dry-down and maturity of wild hosts, the accuracy of the model improves when it is used as close as possible to the actual planting date. The model color codes the level of predicted thrips injury: GREEN=low pressure, YELLOW=moderate pressure, or RED=high pressure. Based on 2019 experiences, a model prediction of RED indicates that an automatic foliar spray will be necessary, even before leaf symptoms are evident.
Insecticide choices for foliar thrips treatments are listed in the Extension Cotton IPM Guide – IPM-0415. They include acephate (Orthene or generics), dicrotophos (Bidrin), dimethoate (or generics), and spinetoram (Radiant or Intrepid Edge, which contains Radiant).
Since the model will likely contact the same weather station even if you plant in multiple counties, it makes sense to simply use one pin as your farm location. However, it is beneficial to run the model with varying planting dates, probably at least once every 7 days. Different regions of the state (North, Northeast, Central, Southeast, Southwest) may have significantly different thrips pressure as occurred in 2019.
To increase our chances of profit for 2020, we need to begin the season with the goal of producing the highest possible yield. Insect-wise, this begins with preventing the yield robbing and delaying effects of thrips injury.