Early season insect pests are among the biggest problems for Mississippi peanut growers, says Jeff Gore, “and thrips are the one I probably get the most calls about, particularly in the Delta.”
There are a number of options for at-planting insecticides, he said at the annual meeting of the Mississippi Peanut Growers Association, and “while they have different strengths and weaknesses, all are good.”
In work at the Delta Research and Extension Center last year, he says, plots were treated with Dynasty, a fungicide package, CruiserMaxx, a fungicide package plus Cruiser, and completely untreated seed.
Gore, who is associate Extension and research professor at the station at Stoneville, Miss., says there were “some serious seed rot problems” in the completely untreated plots that resulted in a 35 percent yield loss because of the cool, wet weather. There was no difference in yield between CruiserMaxx and Dynasty treated seed.
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In another test, Velum Total, an at-planting insecticide/nematicide from Bayer CropScience, was compared to Thimet and Admire Pro.
“Velum Total is imidacloprid and another compound that controls nematodes,” he says. “The higher rate of Velum Total gave a little yield bump at the end of the season beyond what we saw with Admire Pro. We also saw some improvement in insect control with Velum Total over Admire Pro. We can’t explain it, but the Velum Total plants overall looked healthier and didn’t seem to sustain quite as much thrips damage.”
In a test with combinations of at-planting insecticides, Cruiser and Thimet, with foliar oversprays of Orthene or two applications of Orthene, all the treatments yielded better than the untreated control.
Thrips control in peanuts generates many questions each year, he says. “I’d always heard you can’t eliminate a thrips problem in peanuts by spraying over the top, that rows won’t lap the middles as quickly unless thrips are controlled, and that thrips make weed management more difficult. So, I decided to put out a test to try and quantify some of these statements.”
In 2014, plots were sprayed one, two, and three times with Orthene to control thrips. “Compared to the untreated check, we didn’t see any difference in plant growth and time to lap the middles,” Gore says. “After 30 days to 45 days post-planting, there was no difference in growth between any of the treatments.
Treatments increased yields
“But what surprised me when we harvested the trial and got the yield data, was that we could see a stairstepping of yield — each additional treatment increased yield.”
That “goes against conventional wisdom about what we’d always heard about controlling thrips in peanuts,” he says. “It was just one test in one year, and it may be that conditions were just right for us to get that kind of result. We were also pretty aggressive with our herbicide program on the station, where we have a lot of resistant weeds. But I think we need to start looking at interactions between thrips and some of the herbicides we’re using.”
In his work with peanuts, Gore says, “We’ve seen thrips control slipping with Cruiser-treated seed versus Thimet. Cruiser isn’t working as well as it used to, but nevertheless I’m consistently seeing that Cruiser-treated seed seems to be one of the best-yielding products in my tests.
“There are a lot of pests Cruiser will control other than thrips, so it may be that we’re controlling a bit broader spectrum of insects than with other treatments — some of the soil insects that feed on seedling plants below ground and control of various above ground insects, which helps get the plants off to a better start.’
A lot of work has been done with three-cornered alfalfa hoppers, Gore says, and “they rarely cause yield problems in peanuts. We had one cage test, out of seven, where we saw a significant yield reduction from hoppers. In that one test, we had a lot of nymphs, and they tend to girdle pegs a lot more than stems and leaves.
“I wouldn’t worry much about stem and leaf/petiole girdling, but if they are present, I would have scouts and consultants pull up a few plants and look at pegs. If there is significant girdling of pegs, that’s when you can have yield losses.”
Work was started last year, Gore says, on developing “some type of defoliation threshold for peanuts that’s easy to scout and will accommodate the entire caterpillar complex. We did 100 percent defoliation at different times during the season: 35 days after planting and every 15 days after that, through 110 days after planting.
“We wanted to see when peanuts are susceptible to defoliation. Peanuts have a remarkable capacity to recover from defoliation. In our work last year, we had significant reductions in yield with 100 percent defoliation compared to non-defoliated, from 35 to 95 days after planting, and defoliation no longer had an impact once we got to 110 days after planting.”
Don't overuse chemistry
There are “a lot of good products now to control caterpillars in peanuts,” Gore says. “Prevathon and Belt are in the diamide class of chemistry, which is by far the most remarkable insecticide class I’ve ever dealt with — it has very good efficacy and very long residual control of the entire complex of caterpillars that infest peanuts.
“But a potential problem is that this chemistry is labeled and used in every crop we grow in Mississippi, and it may not take long before we use it up. There are other products for peanuts that will do a good a job of controlling these pests and help preserve the diamide chemistry as long as possible.
Intrepid Edge and Diamond are two examples of recently labeled insecticides that will do a very good job of controlling the entire caterpillar complex and provide similar residual control, while helping to take pressure off Prevathon and Belt, Gore says.
“These have not been considered good insecticides for bollworm or tobacco budworm control in other crops, especially Diamond. The insect growth regulators, Intrepid and Diamond, tend to provide better control of defoliating caterpillars (i.e., loopers and armyworms) compared to fruit-feeding caterpillars (i.e., bollworms and tobacco budworms) in other crops such as soybeans.
“However, our tests have shown good activity against both bollworm and tobacco budworm in peanuts with these insecticides. This most likely occurs because all of the caterpillars in peanuts are feeding on the foliage. Essentially, the insects are consuming a much greater dose of the insecticides because they have to consume more leaves than if they are feeding on fruit.
“In a crop like soybeans or cotton,” Gore says, ”a bollworm will bore into the pod or boll, so the only insecticide they are exposed to is a small amount on the surface of that structure when they bore in. Once they are inside the fruit, they are no longer consuming treated plant material.
“In peanuts, these insects feed on leaves throughout their entire life cycle, so they are consuming the insecticide over several days and eventually consume a lethal dose.”