Tuesday, May 9, 2017

Thrips and Grasshoppers Need Attention

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.