The only weapons that cotton producers have for managing insect resistance is their assortment of chemicals and a little foresight. Insects have time and history.
A case in point, according to Michael Boyd, Extension entomologist at the Delta Center in Portageville, is that “since we've used synthetic chemicals, insects have always been able to adapt to whatever products we use. We can't let our guard down.”
This was a driving force behind strict resistance management guidelines and refuges to protect Bt cotton's insecticidal protein, which unlike traditional insecticides, is in the field 24 hours a day for several months.
But growers should understand that insects can still develop resistance to Bt cotton and to foliar insecticides directed at secondary pests in both Bt and conventional cotton.
As to the latter, “We encourage farmers to rotate their chemicals whenever they possibly can,” Boyd said. “Make sure you have an economic problem with the insects before spraying.
“With some of the newer products, they are a little expensive and there is a tendency to cut rates. You have to be careful about that. If you don't get a good kill, it could set up a situation where insects could be resistant to products.”
Don't over-rely on any one class of chemistry, added Scott Stewart, cotton insect specialist at University of Tennessee's West Tennessee Experiment Station in Jackson, Tenn. “People need to be aware that if they are putting on sequential applications in the early season for plant bugs and aphids, they have several different classes of chemistries they can choose from.”
“Sometimes you may have to spend $2 to $3 more to rotate to another chemical, but bite the bullet and do it because it's an investment in the future,” says Missouri Extension cotton specialist Bobby Phipps. “I know money is tight, but resistance is not funny.”