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Changes affecting insect control

Significant changes have occurred in peanut production over the past decade, many of which have impacted insect management, says Steve L. Brown, University of Georgia Extension entomologist.

“Tomato spotted wilt virus has caused tremendous changes over the past decade,” says Brown. “Among other things, the virus has driven variety selection for the past 10 years. If you don't have resistance to tomato spotted wilt in your breeding program, you're not going to make it.”

These factors and more have caused changes in how insects are managed in peanuts, he adds. “One thing we've seen is an increased response to thrips control. If you go back and look at the research — and this was good research — you'll see that it tells us it does not pay to control thrips on peanuts. Thrips makes peanuts look ugly, and it stunts their growth, but with time they grew out of it and there was no yield loss. It didn't make sense to do anything — no Temik, no Thimet, and no Orthene sprays,” he says.

While that was true at one time, it's no longer the case, says Brown. From 1987 through 2001, he and other researchers looked at different options for controlling thrips in more than 100 trials.

“For a long time, there wasn't a consistent trend where we saw a positive yield response from controlling thrips. Then, along about 1997, we started to see a dramatic change. After that, we got a much more consistent response to thrips control.

“In 1997, Georgia Green came on the scene, and that variety apparently is more sensitive to thrips damage. I feel confident saying that it does pay to control thrips in our current environment. We would encourage you to control thrips because we think there is a yield response,” he says.

Yield data from 2001 shows an average yield response from thrips control of 724 pounds per acre from 23 comparisons, says Brown. The range was from 121 pounds to 1,578 pounds per acre.

Another change in insect management has been the increased use among growers of Thimet and Phorate, says the entomologist. “Thimet was the dominant product, and it's still out there. And we're still using a lot of Temik. Our goal at the University of Georgia was not to get people to use more Thimet. But when tomato spotted wilt virus came onto the scene, we started seeing documented responses to Thimet. It wasn't a big response, but we were getting a consistent reduction in the virus where we used Phorate and Thimet,” he says.

Over time, more growers tried Thimet, says Brown, and their initial reaction was that they didn't like it. “It burns peanuts and makes them look yellow for a time. But we found over time that we could use Thimet, burn the peanuts, get our reduction in tomato spotted wilt virus, and still make good yields,” he says.

But Thimet isn't always the best option, says Brown. “If you have nematodes, Temik probably will be your best option.”

Temik and Thimet both are highly toxic materials, he says, and this can become a problem when applying them. The EPA is making an effort to reduce applicator exposure to these products.

“We're trying to keep from handling bags, pouring these toxic materials, and breathing the dust. We have the ‘lock and load’ system, which works great, and the makers of Phorate also have responded to the EPA mandate with a system that reduces your exposure. This system is free from your dealer if you're buying Phorate.”

Another change in peanut insect control has been the labeling of Steward and Tracer, says Brown. “Steward came along at the right time in Georgia, when we were having an outbreak of beet armyworms. Prior to Steward and Tracer, we didn't have anything to help us against beet armyworms. Steward is the most reliable beet armyworm control available to us, and it has other advantages as well. Unfortunately, it's a little pricey. But when you have beet armyworms, you'll be glad to have this product.”

Georgia growers have used a lot of Tracer in the past year or two, he says. “It's a good, broad-spectrum material, covering a lot of the weak spots we had before Tracer became available.”

There also are legal implications with the use of Tracer, says Brown. “There is a pre-harvest interval of three days prior to nut harvest. That's not within three days of digging, but three days prior to nut harvest. This means that we can, at times, use Tracer up until the day of digging. We've never had that before. Everything else has had at least a two-week pre-harvest interval.”

Over the past decade, peanut growers also have seen a decline in the utilization of pyrethroids, he says. “We've used Asana and Karate in peanuts for years, and they've been workhorses for worms, leafhoppers and three-cornered alfalfa hoppers. They also are inexpensive products. They are becoming less effective because of the increasing percentage of tobacco budworms versus corn earworms.

“For years, we called them all corn earworms. They're two very closely related species, and they look almost identical in the field.

“For many years, it really didn't matter which species you had in peanuts. In cotton, it makes a big difference for a lot of good reasons. But over time, and with our increase in cotton acreage, we're seeing a higher percentage of tobacco budworms versus corn earworms in peanuts.”

Pyrethroids, says Brown, aren't very effective against tobacco budworms. “We haven't been able to control that particular insect with pyrethroids, and we've seen a reduced efficacy in cutworms. Cutworms have become more of a problem in the past two to three years. In some cases, we've seen control problems with Asana and Karate. We've never had trouble controlling velvetbean caterpillars, but for the past two seasons, we've seen some indications in the extreme southwest corn of the state that pyrethroids weren't working on velvetbean caterpillars.

“I'm hoping it was just an odd thing blown in from one of the hurricanes. Last year, we had multiple failures in about a three-county area. So I'm getting a little apprehensive about the use of pyrethroids in those situations. I'm not telling you not to use them. I hope they still work, and you might not ever see a problem. It's something we'll have to continue watching.”

Pyrethroids, he says, have never been effective on beet armyworms, loopers or large fall armyworms. But Tracer and Steward are filling that void, he adds.

Another change in the past several years has been a decline in the use of Lorsban, says Brown. At one time, Georgia growers probably were treating 50 to 70 percent of their acreage with Lorsban.

“That has decreased over time. But I think there still are certain situations where it pays to use Lorsban. There are other situations where it doesn't pay. The trick is trying to determine when your chances are the greatest for getting a return on your investment from Lorsban. There's no magic answer, and the toughest question I field is when a grower calls and asks if he should spend $16 to $20 per acre for Lorsban.”

Brown says Lorsban is a good investment in heavy clay soils in the western part of Georgia, due to Southern corn earworms. And this is even truer, he says, where soils are irrigated and remain wet for much of the growing season.

“It doesn't happen every year, but you're buying insurance. There's enough of a threat in those types of soils that I'd use Lorsban every year.”

There also has been a big change in recent years in peanut tillage, says Brown, with more growers moving to conservation-tillage. And this change has had a large impact on insects, he says.

“We're seeing a relatively new insect problem in our peanut fields. It's not a new insect, and it has always been there, but the absence of tillage has made it a problem. When you take tillage out of a system, you see burrower bugs. We had several fields that went Seg. 2 due to damage from this insect, and that's all due to conservation-tillage.”

Conservation-tillage fields also are more susceptible to wireworms, Southern corn rootworms and white grubs, says Brown.

“I'm not saying that you shouldn't use conservation-tillage. The advantages of conservation-tillage probably outweigh any disadvantages from the soil insects. You just need to be aware of the potential problem, and Lorsban may be more of an advantage in those situations.”

There also has been a reduction in recent years of white mold pressure in Georgia peanut fields, says Brown. “When we were using a lot of Lorsban, it was going towards white mold suppression. This was before Folicur, Abound, Moncut and the other good fungicides came on the market.

“Now that we have better fungicides, we don't really need Lorsban for the white mold problem. But, data continues to show that even where you're using Folicur and Abound, particularly in a reduced rate situation where you're trying to reduce costs, Lorsban actually will give you a little bit better white mold suppression.”


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