While producers have had problems with bollworm control with pyrethroids in cotton, grain sorghum, and soybeans, the materials continue to be an effective means of managing the pest, says Ryan Jackson.
“Although we’ve seen some decrease in control of bollworms with pyrethroids, these materials are still the best option,” he said at the annual meeting of the Mississippi Agricultural Consultants Association at Mississippi State University.
“As with all pesticides, use best management practices to maximize the effectiveness of pyrethroids, such as using appropriate spray nozzles and volumes and making applications when worms are small to obtain the best control.”
Cutting pyrethroid rates and “throwing a pyrethroid in the tank just because a tractor is going across the field also can lead to an increase in exposure and tolerance,” says Jackson, who is USDA-Agricultural Research Service research entomologist at Stoneville, Miss.
Monitoring for bollworm resistance has been conducted in Mid-South states for several years, he notes, and “we’re definitely seeing a shift in survival rates in our monitoring programs, particularly in the Louisiana historical dataset that extends from the late 1980s to the present.
“Typically, we’re seeing the peak of resistant bollworms in late June and July. Many of these developed on corn and then moved into cotton.”
For the past several years, research projects in the Mid-South states have been looking at resistance of bollworms to pyrethroids.
“During the period, we saw a 59 percent increase in survival rates in Arkansas, 64 percent in Louisiana, 98 percent in Mississippi, 34 percent in Missouri, and 68 percent in Tennessee.
“In milo, we used to be able to apply very low rates of pyrethroids and get control, but in some situations we’re no longer seeing that level of control. Bollworms are exposed to pyrethroids in cotton, soybeans, milo, and other crops during several generations within a season, and this amount of exposure eventually leads to resistance development in most insects.”
Some new products are coming along that may provide some help in controlling bollworms, Jackson says, “but they will be expensive.”
In other areas of insect control, there have been questions about potential resistance of bollworms to Bollgard II technology in cotton, according to Angus Catchot, Mississippi Extension associate professor of entomology and plant pathology, who also spoke at the MACA meeting.
“I think the technology is sound,” he says. “We’re not seeing resistance issues that we can document.”
In Mississippi tests, end-of-year boll damage was reduced 47 percent with Bollgard cotton and another 74 percent with Bollgard II.
“In 2009, we had a lot of eggs and worms and a lot of Bollgard II acreage was sprayed last year,” Catchot says.
“Currently, we use a threshold of 4 percent larvae in Bollgard II cotton prior to cutout — the same as for non-Bt cotton — and I feel we could easily double that threshold with no adverse effect on yield. But threshold work in Bollgard II cotton is difficult to conduct in the Mid-South because there are only a handful of fields that actually exceed 5 percent boll damage, regardless of the initial infestation.
“We do occasionally see infestation levels that would certainly justify a treatment, but these are the exceptions and generally occur less than 1 percent of the time in our area. The difficult becomes, how do you manage for the exceptions?”
“Producers are paying a lot for this technology, and they want to get the most value from it, but it’s difficult to make treatment decisions in these situations. Eventually, researchers will have to work out a threshold that takes into account some level of damage with these newer technologies.”
Commenting on new insecticides in development, Catchot says, “There is not a lot of new chemistry these days.”
Development of new materials is increasingly more costly, he notes, and the Environmental Protection Agency “has not been very friendly” toward registering new chemistries.
For materials to reach commercialization, he says, they must have short environmental persistence, low use rates, low toxicity to non-target species, manufacturing costs that will allow a profit, and a delivery system that acts on or within the plant — a combination that is increasingly difficult to achieve economically.
Among new insecticide materials in the pipeline, Catchot says, are:
• Sulfoxaflor ISO from Dow (no trade name yet). “We’re excited about this one. In my tests, it has been very effective on plant bugs and aphids at low use rates.”
There is some flexibility in rates, he says, with up to six applications per season.
“In nearly every trial we’ve done, it has given control equal to or better than standard materials.”
Commercialization is expected in 2012.
• Belay, a third-generation neonicotinoid pesticide from Valent that is foliar- and soil-applied on numerous crops, including cotton, soybeans, sweet potatoes.
“In a red-banded stink bug test, alone and with a pyrethroid, it provided surprising control,” Catchot says.
• Belt from Bayer CropScience is currently labeled for cotton, but soybeans will be added, perhaps this season.
“It has looked very good against soybean loopers and a number of lepidopterean pests.”
• Coragen from DuPont for cotton, potatoes, and leafy vegetables. “It is highly toxic to lepidoptera at low rates,” Catchot says. “The residual in the field is pretty amazing for a foliar product. The limiting factor right now is its price for applying on cotton.”
• Spinetoram from Dow for thrips control in cotton. “This is potentially a good material for controlling thrips without flaring spider mites,” Catchot says. “The addition of a surfactant makes a world of difference with this product on thrips.”
A number of products are coming or have recently been registered in pre-mix or co-packs of insecticide products, he says, among them Leverage 360, Brigadier, Hero, Volium Xpress, Volium Flex, Cobalt, Tourismo, Agri-Flex, and Athena.
With the emphasis on IPM for transgenic crops, companies are “moving really quickly” to offer combinations of genetic traits to meet a wide variety of crop management situations, Catchot says, and it is going to “increasingly be a challenge to understand where these combinations fit.
“And if we think cotton trait combinations are confusing, corn is increasingly complicated in terms of trait combinations, modes of action, etc.
“In addition, there are going to be numerous seed treatments, which will add to the challenge for farmers and their consults in figuring out what they need in terms of traits and treatments.
“It likely means,” Catchot says, “that farmers will have to start ordering earlier in order to get a particular brand with the particular traits and treatments they want.”
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