By Jim Steadman
While many growers may be finalizing their cotton plans and getting planters ready for the field, it’s also a good time to start thinking about managing early season insect pests, especially thrips.
“In normal years, we usually have to overtreat 20-to-30 percent of our cotton acres on top of the seed treatments for thrips,” stated Angus Catchot, Extension entomologist with Mississippi State University. “But for the last two years, for a variety of reasons – maybe cooler weather, maybe residual herbicides holding the cotton plant growth back a bit – we’ve had to make multiple applications on up to 70 to 80 percent of the acres. That’s a trend that may be with us for a while.
“We need to be especially careful when we have to do that,” he added, “because we can flare early season spider mites if we’re not careful and choose the wrong chemistry.”
Southern growers have to deal with two different species of thrips – the more common tobacco thrips and the tougher-to-control western flower thrips. Tobacco thrips are easily controlled with organophosphate chemistries like Orthene, Bidrin or dimethoate. However, early season use of Orthene is likely to flare spider mites. A newer product, Radiant, won’t flare spider mites and is the only product showing decent activity on western flower thrips, but at a higher cost than other products.
The key is thorough, early season scouting.
“We need to know what species we’re dealing with so we know what chemistries to use,” explained Catchot. “We don’t want to treat unless we absolutely have to. We need to protect cotton so it can grow off and get a good start. But we also don’t want to go into plant bug spraying with three sprays already out for thrips.
“Generally, with a few exceptions, once cotton gets past the fourth leaf and is growing off well, we can stop worrying about thrips.”
With projected increases in grain acres and decreases in overall cotton acres, it’s also worthwhile for growers to look at where their cotton will go, if possible, especially in relation to corn.
“One of the things we strongly recommend is to try to block your cotton away from your corn if you can,” said Catchot. “We know we can’t always do that, since fields share wells – and you certainly can’t control what your neighbors do. But as we see more and more corn, we can certainly minimize some of those edge-to-edge effects.”
Of course, early season insect skirmishes just set the stage for the battles yet to come with later-season pests.
“Plant bugs are always going to be our number one issue,” reminded Catchot. “And the fewer acres in cotton may even escalate the problem to some extent. We’ll have to wait and see.
“Bollworms are very dependent on corn,” he continued. “Even though nearly 98 percent of the cotton planted is two-gene cotton, we routinely have to make overtreatments for escapes. Where we see escapes above economic thresholds, we certainly see yield benefits from overtreating. “We often tankmix pyrethroids with OPs for tarnished plant bug control during bloom, and that is sufficient for bollworm escapes. But if we continue to see pyrethroid efficacy decline on bollworms in cotton, we’ll likely have to add the diamide chemistry in some situations.”
In spite of a warm winter last year, big bollworm flights just didn’t materialize as expected. So, what about this year?
“This winter wasn’t a killing winter, but I’d say it was more of a normal winter,” he stated. “There’s no question that we’re going to deal with bollworms with all of the corn we have now. But to what extent, it’s going to be as hard to tell as it was last year.”