Insect Pests Make Waves in 2011

Given average mid-season conditions, insecticide applications in the Southeast are winding down. In the Mid-South, they’re just getting started.
 
“Virginia and North Carolina assuredly lead the rest of the Cotton Belt in thrips problems,” says Dr. Jack Bacheler, North Carolina Extension Entomologist. 
 
Then once the thrips-damage window closes, foliar insecticide applications in the Southeast tend to drop off. 
 
“Damage on two-gene cotton by any caterpillar species in North Carolina is down in the 0.5% range. So that’s not a really high priority,” Bacheler says.
 
But due to the decrease in Temik availability – Bacheler says 70% of North Carolina’s acres in 2010 received a Temik treatment – 2011 is setting itself up as anything but average. 
 
“We’re having a big thrips year, and that’s going to translate into more than one foliar application in some cases, in addition to the seed treatment,” he explains. “If you don’t have Temik down, the odds of having to treat for spider mites or aphids goes up a lot – say an average of 8- to 10-fold. So certainly in a year where we’re using a lot of insecticides for thrips and much less Temik, they could be more of a problem.”
 
Meanwhile in the Mississippi Delta, growers averaged six sprays for plant bugs alone in 2010. “Which is right up there with most years,” says Mississippi Extension Entomologist Dr. Angus Catchot. 
 
But Catchot says plant-bug control in the Mid-South is improving.
 
“The difference in 2010 was that, although we were treating threshold numbers in a lot of places, we weren’t treating ‘2X’ and ‘3X’ numbers like we’ve had to deal with in previous years on as many acres,” he says. “Overall, we did a better job of keeping numbers down with foliar sprays because overall population numbers were not as high.
 
“One thing about plant bugs – and it’s something I think all of us in the Mid-South agree on – is that cotton is not really a source; it’s more of a sink. In years where we have low cotton acres, plant bugs are more concentrated in the acres that we do have since they’re increasing their numbers on other crops and wild hosts.”
 
Because of Mississippi River flooding in the Mid-South, much of the Delta region was planted late. And that, too, could make insect pressure this year anything but average.
 
“We have a lot of cotton that is planted after May 15, and many acres were replanted due to hail and sand blasting,” Catchot says. “Anytime we have a late crop, it sets us up for more problems with late-season plant bugs. Our consultants have done a great job of utilizing the tools available to get the most out of them, but we still desperately need new chemistries to add to our toolbox.”
 
Weather Matters
Both Bacheler and Catchot agree that weather conditions also affect insect pressure. 
 
“Our main mid-season pests are stinkbugs in the Southeast,” Bacheler says. “There’s a good correlation between how wet or dry it is and stinkbug problems. In North Carolina, for example, about 4% of our crop is irrigated. So that means if the weather turns dry, the cotton becomes a lot less attractive to stinkbugs. If that happens, we just won’t get a lot of stinkbug damage in those kinds of years. Whereas if we get more generous rainfall, cotton and other hosts are doing better.”
 
Adds Catchot: “It really has a lot to do with what kind of spring we have. It doesn’t matter how well plant bugs survive the winter. We could have a really hard winter that reduces plant bugs, then a very good spring, and they can blow up and be a big problem. Or we can have a soft winter and have a lot survive, then a very poor spring and the numbers will drop. This year we had good rain and the wild host plants were abundant, so I would expect that we’re going to have pockets in the Mississippi Delta that will have the high populations of plant bugs that we’re accustomed to.”
 
Mixing Crops, 
Mixing Chemistries
The crop mix in each area is another concern when it comes to insect populations in cotton. 
 
“As corn begins to dry down, spider mites are ballooning everywhere across the landscape. No matter whether you did everything right, or everything wrong,” says Catchot. “As corn dries down, they’re going to move out and find their way to cotton. We have been sampling corn fields for mites in the Delta over the last few years and it is difficult to find a field where mites are not present at some level. We’ve talked at length with growers about trying to block their corn and cotton away from each other.”
 
Adds Bacheler: “Let’s just say stink bugs are on wheat early, and they move on to field corn, and then into peanuts and cotton and soybeans. They tend to feed on the fruiting parts of things, and in wet years, the plants are doing better and higher populations seem to build up. Everything from pecan trees to other hosts are just doing better, and we just seem to have quite a few more stinkbugs, and therefore greater potential for damage.
 
“Where we have cotton next to corn, spider mites can be a problem,” he continues. “And if this year stays hot and dry, they can build up pretty high numbers in field corn and move into other crops.” 
It’s universally accepted that alternating modes of action, or tank mixing modes of action, increases efficacy and decreases the chances of resistance developing. 
 
“We’re starting to learn how to use the chemistries a little better, given the problems we have with resistance,” Catchot says. “We’ve really pushed mixing pyrethroids with organophosphates after bloom. 
 
“We’re learning how to use Diamond – an IGR – better, and we’re incorporating it into the system earlier – around the third week of squaring to first bloom. It only has activity on the immatures and affects them when they try to molt. But when the adult female is exposed to Diamond, it reduces the number of eggs they lay and the viability of the ones they do lay.” 
 
For stink bug control, know your species. Green stink bugs can be effectively controlled with pyrethroids, while brown stink bugs are better controlled by organophosphates, like Bidrin.
“Pyrethroids do a very good job with green stinkbugs, and are, of course, very inexpensive,” says Bacheler. “But in a lot of the Southeast, brown stinkbugs are definitely part of the species composition. So for us, it’s very common for growers to use at least some Bidrin, and more often than not it will be mixed with a pyrethroid.”

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