By Steve Byrns, Texas A&M AgriLife Extension
Insect damage to crops is ramping up across Texas, said Dr. David Kerns, Texas A&M AgriLife Extension Service integrated pest management state coordinator in College Station.
“We have been seeing a great deal of bollworm activity in Bt cotton, and there have been quite a few insecticide applications going out,” he said. “A lot of these reports have been coming out of the Wharton and Corpus Christi areas, but the problem is not confined to just those locations or to only cotton.
“In the Brazos River Bottom, we had a field of WideStrike cotton that virtually had a worm in every terminal and as much as 40% fruit loss in the upper third of the canopy. We have reports of unacceptable injury in some TwinLink and Bollgard 2 varieties as well.”
Kern is asking producers with Bt cotton exhibiting unacceptable bollworm injury to let him know (979-845-2516, email@example.com), as he would like to make further collections.
“Be sure to give the technology the opportunity to work, though,” he said. “Our research has shown that if you are running 6% injured fruit with live larvae present, it pays to spray. That said, if I had a very large egg lay in WideStrike technology, I would be inclined to spray. Make sure you check blooms, bracts and bloom tags for eggs and small larvae. A great many of the egg lays we are seeing are not so much in the terminal but in the canopy.”
Kerns said the most common insecticide choices for bollworm control are pyrethroids. Blackhawk at 3.2 ounces per acre, Prevathon at 14-19 fluid ounces per acre and Besiege at 7-10 fluid ounces per acre are common treatments.
“Be careful with the pyrethroids,” he said. “Granted, they are inexpensive, but we have had some reports of control failures, especially if the bollworms are second instar or larger when sprayed, plus they can flare aphids and spider mites.”
Grain sorghum is also on the bollworms’ menu this summer, Kerns said.
“Bollworms are also hitting grain sorghum and if you catch them small – in the first and second instar stage – pyrethroids usually will control them, but rely on Blackhawk, Prevathon or Besiege if very many large worms are encountered.”