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Pesky Spider Mites Won’t Go Away

By Tommy Horton
Editor

 
Spider mites defy description. In fact, it’s difficult to understand these cotton pests and put them into the proper pecking order with today’s other insects.

They never did as much damage as boll weevils and certainly can’t be mentioned in the same conversation with plant bugs. That puts them somewhere in the middle of the pack.

Don’t be deceived by their middle-of-the-road ranking among pests that cause extensive damage to cotton each year. Barring any change in trends, they are quickly becoming one of the most troublesome pests in today’s ever-changing insect complex. These microscopic critters have always plagued cotton plants, but it’s only been in the last five years that they have caught the attention of entomologists and producers.

In 2005, a serious outbreak of spider mites occurred in the Mid-South – primarily in Mississippi. At the time, entomologists thought it was a one-time incident. Since then, spider mite infestations have occurred every year in the region.

“This problem isn’t unique to Mississippi,” says Extension entomologist Angus Catchot. “Out in California and Arizona, they’ve also had to treat for early season spider mite outbreaks. That’s why we looked to them to take advantage of their expertise.

“The fact that they are becoming a season-long pest is a new experience for us here in the Mid-South.”

Serious Damage Inflicted

In Mississippi State University’s official 2008 report on cotton insect losses, 181,415 acres in the state were reported as infested by spider mites, with 106,829 acres treated. The average treatment cost was $21.85 per acre, and 3,074 bales were lost due to spider mite damage.

Several factors potentially are contributing to the mite outbreaks:

• Less-than-clean fields at planting

• No-till or minimum-till practices

• Proximity to corn fields

• Any stubble or vegetation in fields

• Henbit or evening primrose weeds

• Other weeds on ditch banks

The major symptoms of spider mite outbreaks center on the timing of infestations. Catchot says mites traditionally were known as “cutout pests.” They would only show up later in the season. Now, because of new environments, they are visible during the entire crop season.

“Occasionally, you can have an unexpected pest outbreak in any year,” says Catchot. “What has happened since 2005 is that this has become a consistent threat. In some areas of the state, it’s a season-long problem. All of this has definitely surprised us.”

Several Options Available

Entomologists are working on various tactics to control these pests, and Catchot says several insecticides and miticides are effective. The challenge is convincing a producer to make an expensive application to control this particular pest.

Some of those products include Syngenta’s Zephyr, Valent’s Zeal, Bayer’s Oberon, Nichino’s Portal and Chemtura’s Comite II. Meanwhile, the problem has become serious enough that other producers are simply increasing their early-season applications of Temik.

Catchot says researchers also are recommending different cultural practices. Those include identifying early-season vegetation hosts, burndown options and intensive scouting.

“The advice that I like to give producers is go ahead and make a spray application if you have 40 percent of your plants infested and the conditions are hot and dry – and do it before you have severe symptomology,” he says.

Developing a strategy for controlling spider mites also is compounded by the complicated nature of what causes outbreaks. As Catchot says, a number of factors contribute to the problem. Just as plant bugs became a major threat after the boll weevil was eradicated, spider mites became more serious because of changes in farm management strategies and crop diversity.

Perhaps the most progress has been made in convincing producers not to make a broad spectrum pyrethroid or acephate spray. This seems to always cause a flaring of spider mites if they are present in the field.

“I have seen that happen numerous times,” says Catchot. “I really think our consultants and producers do a great job in avoiding unnecessary applications that flare spider mites. They also don’t automatically make a thrips spray when they’re in these spider mite areas of a field.”

Big Factors: Corn, No-Till

Two situations apparently are contributing to the problem, and there isn’t much that can be done to change them. Corn acreage is a known host environment for spider mites, and they can easily migrate into cotton fields.

Another factor is the popularity of no-till and minimum-till practices. Leftover stubble in the field is a perfect overwintering environment for mites.

“Sometimes it might seem like a no-win situation for farmers,” says Catchot. “But the priority should be in scouting those fields and getting on top of the problem before it spreads.

“We don’t want to scare anybody. Spider mites can be an expensive problem, and that’s why you need to scout and spray when necessary.”

Spider mite infestations are serious enough that treating for this pest is sometimes a determining factor in whether some producers planted cotton in 2009.

That fact troubles Catchot.

“We have seen cases where producers in the central and south Mississippi Delta have chosen not to plant cotton because of the high costs of treating spider mites and plant bugs,” he says. “That really bothers me, and it’s why we’re working on this problem to find an answer.”

Contact Tommy Horton at (901) 767-4020 or thorton@onegrower.com.


Texas Battles Mites

Spider mites have always been present in cotton production, and they are not limited to one region. Some of Catchot’s entomology colleagues across the Belt report similar outbreaks in recent years.

Megha Parajulee, associate professor and cotton entomology project leader at Texas AgriLife Research and Extension Center in Lubbock, has observed increased spider mite populations on the Texas High Plains for several years. He says most producers are aware of how serious the pest has become.

“I don’t know if it’s unusually erratic weather events or varietal shifts during the last few years, but we definitely have seen some increases in spider mites in the High Plains,” he says.

The problem, however, isn’t as serious as what confronts Mid-South producers. Parajulee says most spider mite outbreaks in the High Plains occur late in the season.

“The situation isn’t that bad here in Texas,” says Parajulee. “But it’s an insect pest that we are watching. We know what’s happening in the Mid-South, and that concerns us.”



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