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.
