Early season cotton seedling insect activity is
heating up. Both grasshoppers and thrips
need attention this week (May 8-12).
Cool (cold) nights last week slowed down the growth of cotton seedling
on our earliest planted cotton. This
will serve to keep cotton in the thrips susceptible stage longer. At the same time, where we have had multiple
rain events, we likely have lost some of our at-plant thrips protection
chemicals to leaching. This would be
true of both seed treatments and in-furrow sprays. Cotton planted on or after May 10th
should have reduced thrips pressure and less need of a foliar spray.
Cotton that is emerging in the next several weeks will
be at some level of risk from grasshopper feeding. Immature grasshoppers are abundant in fields
statewide from the Florida line in the South to Tennessee line in the
North. These immature, up to thousands
per acre, will jump when disturbed but cannot yet fly. A few grasshoppers have already spent 30-50
days as immatures and are already in the adult stage. The most susceptible stage of cotton to
grasshopper damage is the “crook” stage just as it emerges. Damage at this stage kills the plant leading
to reduction in stands. Seed are too
expensive to plant a few extra for these grasshoppers. This is the reason I would suggest that
growers treat on damage potential or risk, and not on thresholds. In fact, it would be difficult to establish a
threshold since grasshopper feeding on cotton is unpredictable. Immature grasshoppers can be controlled with low
rates of several cotton insecticides.
These include acephate, Bidrin, Lorsban, pyrethroids and others. A couple of ounces of Dimilin added to the
spray would add to the residual control of late emerging or migrating
grasshoppers. Immature grasshoppers
require 30-50 days to reach the adult stage.
Development may be somewhat quicker with warmer weather which we
incurred in March and April. Adult
grasshoppers are very difficult to control.
Even the highest labelled rates of insecticides often do not give 100%
control. If growers observe a need for
grasshopper control to minimize stand loss risk, sooner is better than later to
apply these controls.