Insect Strip

Insect Strip

Friday, June 24, 2016

Early Summer Pest Update

Last week on June13 while sampling field plots in corn near Hart, Tx there were extremely heavy thrips pressure. Clouds of thrips hovered around us while walking through the corn field. These heavy thrips densities had dispersed when sampling the field plots on June 20. But, the thrips had cleaned up the spider mites that were beginning to develop in these fields. We could find a few spider mites away from the field edges. Can we expect that spider mites will not be able to build back or with fewer spider mite numbers and fewer spider mite predators will the mites develop to damaging infestations? So, it still should be prudent to continue scouting for spider mites. And, for late planted cotton with fewer than five true leaves scouting for thrips should continue. 

Southwestern corn borer moth activity has begun to increase in a few counties on the Texas High Plains. So far, the SWCB moth activity primarily been in Dallam, Deaf Smith, and Moore Counties. These moths are coming out of overwintering and are laying the first generation eggs in the whorls of corn. Bt corn will provide good control of the larvae hatching for this egg lay. Even for non-Bt corn this first  generation larval infestation usually does not cause significant damage. Begin looking for shot-hole damage to get an indication of the percentage of plants that are infested. Infestations rarely exceed 5 percent infested plant. Even if there is a higher percentage of infested plants, control treatments may not be effective since larvae may be deep in the whorl where the insecticides will not penetrate or the larvae may have already tunneled into the stalk.
Southwestern Corn Borer - Shot Hole Damage. Photo: Dr. M. Rice

Seeing any Unexpected Insect Damage to Cotton and Corn

On June 19, Dr. Pat Porter posted this article on the Focus on Entomology newsletter. This post has some important information to consider regarding Bt corn and Bt cotton. 
He wrote, “It has been 20 years since Bt corn and cotton were put on the market, and we are now seeing signs that some of the Cry toxins in Bt crops are less effective than they once were. It is certain that fall armyworm is resistant to Cry1F in parts of the country (but not known to be resistant on the High Plains), and corn earworm/cotton bollworm is showing elevated levels of tolerance to several of the toxins in Bt cotton and corn. I want to make it perfectly clear that I am not suggesting we have resistance on the High Plains, but, given what is happening elsewhere in the country, I am saying that it would be prudent to begin watching our fields for elevated levels of damage from fall armyworm, corn earworm/cotton bollworm, southwestern corn borer and western bean cutworm. (This also goes for corn rootworm that is known to be resistant to at least one toxin in Bt corn.)
On top of this we have the old world bollworm, Helicoverpa armigera, knocking on the southern door of the U.S.A., and it may bring with it resistance to some Bt toxins. This species is indistinguishable from our domestic corn earworm/cotton bollworm, except by dissection of the adults. The Texas A&M University Department of Entomology and the AgriLife Extension Service have rapid sampling teams ready to collect from fields that might have H. armigera

This post is a request for growers and consultants to report any signs of higher than normal damage to  corn and cotton regardless of whether they have Bt or not, but especially if they have Bt. We can visit a field and determine whether the damage is within the bounds of "normal" and, if not, we can collect insects for resistance and/or H. armigera screening. My office phone number is (806) 746-6101. Pat Porter” Also, please contact me, Ed Bynum, at (806) 677-5600.