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Cotton Susceptibility to Insect Damage Down
Last weekend’s rainfall helped many but still left others high and dry. Light trap levels of bollworm moths continue to pick up, perhaps somewhat aided by recent rainfall. However, our projected 7-day forecast for much of the state generally looks like a continuation of hot dry conditions. This will certainly be an early-maturing crop overall.
I realize exceptions are probably common, but many areas now have cotton that has been cut out for several weeks, with a very few fields even beginning to open. Many of the other fields have either greatly diminished blooming or have stopped blooming altogether. In these above situations, remember that cotton is quickly becoming unattractive to both bollworms and stink bugs. Even in rapidly growing cotton with plenty of blooms and good moisture levels, the 7th or 8th week of bloom signals the raising of the internal damaged boll threshold to the 20 to 30% range, making the need to treat less likely. In many of our cotton fields, bolls are now too mature to be damaged by stink bugs.
During the next few days and weeks, perhaps our most significant task will be cull out cotton fields that are no longer susceptible to insect damage, and place a higher scouting priority on those fields that still contain susceptible bolls. As a general rule of thumb, fields that are no longer blooming will not likely be attractive to or damaged by insects.
We had had some recent calls about fall armyworms feeding on pastures but none on cotton. The fall armyworm race that feeds on pastures (the grass race) is different than the one that can damage cotton. Additionally, both Bollgard II and WideStrike cotton lines are quite resistant to fall and beet armyworm damage, so we’re probably safe from these species. The cases that I have seen fall and beet armyworms and European corn borers on WideStrike or Bollgard II cotton at economically-damaging levels in parts of cotton fields was almost always when a particular host weed was burned down late in the spring and the half-grown larvae were able to transfer to the Bt cotton. Even these cases are rare.
Additional rainfall in the coming days or weeks would be welcome to help fill out bolls that are generally on the small side this year due to our hot and dry conditions.
I’ll see you again next week on August 10. See you then.