The New Mighty Mite
May 11, 2009 There is one very distinct difference in the two spotted spider mite and every other cotton insect.
That would be that the spider mite is not an insect at all. It truly is a spider, and as such is a member of the arachnids class that includes over 100,000 species.
In years past, the spider mite that tended to show up only during weather extremes. It its case, it was hot, dry conditions. But over the last couple of years, that’s started to change and mites are becoming a season-long problem.
“Spider mites have been around since we’ve been keeping records on cotton,” says Dr. Angus Catchot, Mississippi Extension entomologist. “But what has changed is the severity of the problem in the Mid-South. We’ve always considered spider mites to be a late-season problem and we sort of designed our thresholds around that.”
But starting in 2005, Catchot says it became evident that spider mites were becoming much more of a season-long problem. “In some areas we were finding them when cotton was coming out of the ground. They have been very consistent since then.”
Spider mites damage cotton by feeding on the bottoms of leaves and puncturing individual cells. When the cells rupture, reddening of the leaves occurs. “If it’s bad enough, the plant will actually defoliate itself,” says Catchot.
There’s no definitive data yet to say exactly why spider mites have become a season long problem, but a good bet would be that it’s a combination of several factors. There is the unpredictability of a naturally occurring fungus that comes and goes, the increasing use of on-seed treatments and broad-spectrum applications of foliar sprays that eliminate beneficials, the decrease in the use of Temik and crop mix.
There are several beneficial insects that feed on spider mites and prevent them from flaring, including pirate bugs, big-eyed bugs and other predatory mites. Believe it or not, the western flower thrip feeds on spider mite eggs.
Crop Mix
The increase in corn acreage in the Mid-South had been blamed most notably for the increase in problems with cotton bollworms and plant bugs, but now it may be time to throw the spider mite into the mix.
“Corn is a major player in this,” says Catchot. “I don’t think we have a full appreciation yet of just how much. With corn, I’m talking about late season. We’ve been in corn in the Delta region and there are almost always a lot of spider mites. When corn starts drying down, there’s a mass exodus out of corn. In cotton in the Delta, it really doesn’t matter what you did right or wrong, you’re going to have spider mites late in the season.”
And Catchot says the move to no-till over the last 10 years has to be considered as well. “We know they’re out there surviving on winter annuals.”
That is a point not lost on consultant Billy Beegle who has clients in west Tennessee and the Missouri Bootheel.
“We’re leaving green vegetation in the field all winter long and that gives them a host,” he says. “We’re allowing the vegetation to stay there, sometimes up to two or three weeks prior to planting. So when we put the cotton in the ground, there are already mites there.
“They’re waiting on something new and tender and green to come up ― and that happens to be our cotton.”
Beegle is seeing a shift back to Temik among his growers and they are remembering why they liked it. “It seems to give us early season suppression that keeps them from building up so rapidly,” he says. “We used to go with 3½ pounds for thrips control, but we’ve increased that to 5 pounds. We’re even sidedressing with 10 pounds around the edges of fields in-season that are perennial hotspots.”
Something New
Among the newer foliar insecticides recommended are Syngenta’s Zephyr, Bayer’s Oberon, Nichino America’s Portal and Valent’s Zeal.
Jim Kirkpatrick, a Professional Crop Advisor in Pinal County, AZ, has been working with, and recommending, Zeal.
“Zeal is one of the premier miticides on the market right now,” he says. “You don’t need to start using it at the first sign of spider mites, but you need to before you have what we call out here ‘lightning strikes.’”
Zeal is a mite growth regulator that has contact activity on spider mite eggs, larva and nymphs. Eggs laid by adults that have come into contact with Zeal will not hatch. And as a translaminar, it moves through the leaf from top to bottom.
“I’ve put it on at every level of pressure you can have and had it work,” says Kirkpatrick. “It’s a very effective products. The best thing I can say about it is that it works as advertised.”
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