Thursday, July 19, 2018

Bollworm situation: West Texas cotton

I am glad folks are paying attention to what is happening in other areas. I had a few calls regarding bollworms this week--mostly in response to the hubbub in Central and South Texas. So far, worm pressure in cotton have remained light for the most part with some areas (e.g. parts of Swisher, Floyd, and Hale counties) just starting to show increase in numbers.

Our Bt sentinel research plots at Texas A&M AgriLife Research and Extension center in Lubbock are showing a few worms in non-Bt plots—no activity has been spotted in any of the Bt technology plots so far. As the season progresses, we may see increase in moth flights and the egg lay.

I wouldn’t spray for bollworm egg lay in West Texas cotton as very few eggs make it to worms (thanks to beneficials!). Treatment decisions should be made based on the amount of fruit injury and the presence of live worms in both Bt or non-Bt fields. Since newly hatched larvae must feed on the plant for the Bt toxin to be effective, delay decision making until you can determine the survivorship of larger worms. The threshold level before bloom is 30 percent or more damaged squares with worms present. After boll formation, the threshold is 6 percent or more damaged fruit with worms present.

Many of you are aware of the situation of worms breaking through some of the Bt traits across various cotton producing regions including the parts of Texas. We may experience similar events in the High Plains cotton if it turns out to be a heavy bollworm year. For now, let’s hope it remains a quiet one but don’t let your guard down. Irrespective of what Bt traits you have, keep scouting and be on the lookout.  Remember, once worms increase in size and dig into the lower plant canopy, it’s hard to get them even with the most effective diamide insecticides.