Wednesday, July 19, 2017

Texas High Plains Cotton: Stay Vigilant for Bollworms

Suhas Vyavhare, Extension Cotton Entomologist, Texas A&M AgriLife Extension Service

We have a wide range of cotton out in the field. Early planted fields are in bloom while some of the late or replanted cotton is a little behind. Overall, insect pest pressure remains light. Cotton fleahopper wouldn’t be an issue post bloom, however, the younger cotton should continue to be monitored for fleahoppers.

I haven’t come across any significant worm activity in the region yet. However, with the cotton blooming and the recent rain putting on some new extra growth, bollworm moths can be attracted to it. With so much talk going around with bollworms breaking Bt shields in south Texas and other parts of country, we need to be more vigilant. Treatable levels of headworms (bollworms) have been spotted in some of the sorghum fields around, which also warns of a potential threat in cotton.

I wouldn’t rush with insecticide application just seeing egg lay or the smaller (<1/4 inch) worms in Bt cotton; worms first need to feed on plant for the technology to show its effect. Similarly, I wouldn’t pull the trigger in non-Bt cotton based upon egg lay because natural control often helps keeping bollworm numbers in check. Give the technology (Bt traits) and the predators a chance to work their magic first.

The extent of fruit damage and the presence of live worms should be taken into account while making decisions about insecticide applications. The threshold is 6% fruit injury (post bloom) with the presence of live worms in both Bt and non-Bt crop. Some of the old data indicates pyrethroid insecticides may still work against cotton bollworms but no recent susceptibility data are available from the High Plains. The diamides (Prevathon and Besiege) are the most effective insecticides. Besiege contains both a diamide and a pyrethroid so it would be a better choice if stink bugs are present too. If stink bugs aren’t an issue, prevathon is a better option--it is always good to avoid unnecessary pyrethroid applications to keep secondary pests (aphids and spider mites) at bay.