Insecticides: Making the Most of Limited Chemistries
While no widespread, plague-like insect infestations hit growers in 2017, a number of traited Bt crops continued to struggle under heavy pest pressure — and growers found some soybean aphids are slipping through go-to controls.
New active ingredients are few and far between, so insecticide manufacturers are getting creative. Here, CropLife® takes a brief look at problems in fields and new strategies for combatting them in 2018.
Corn Problem Spots
In Indiana, Dr. John Obermeyer, Extension Specialist with Purdue, says Western bean cutworm made a strong appearance in northern counties. Once growers and pest managers realized the problem, many tried aerial foliar insecticides, but most were too late because the worms had reached ears.
The cutworm was first seen in the state in 2006, with first actual damage noted three years later. At one point, researchers actually thought the pest was disappearing, thanks in part to control from the Cry1F Bt trait in corn hybrids.
“It’s come back with a vengeance,” says Obermeyer. “In northern Indiana in 2016, a few growers and researchers noticed that the trait was starting to falter — then in 2017 it really hit the fan. It’s the old typical textbook scenario where over-reliance on any one given control mechanism, whether a pesticide or trait, falters.”
If growers did find the cutworm thanks to scouting this year, timely application of any of the newer generation synthetic pyrethroids worked well.
And in a more unusual development, slugs came on strong in the state. What worked here? Pretty much nothing. “Desperate times call for desperate measures,” says Obermeyer. “Growers applied metaldehyde baits, sprayed high-salt fertilizers (e.g., 28%) and even used ill-advised organophosphates.”
One big reason for the slug problem is the growing use of cover crops in many parts of the country. In Indiana, estimates place the number of acres planted at around one million.
“Point being, as we increase vegetation and residues in a field, we make them more habitable for these mollusks/slugs, Obermeyer says. “Populations build slowly, over more than one season. All of a sudden, farmers are missing stand in an area of a field. Then when they try to go out and replant it, the same thing happens.”
Cover crops can also bring in other insects, including wireworms and grubs, cautions Jim Lappin, Crop Marketing Manager, Corn & Soy with AMVAC.
In addition, he reports growing corn rootworm issues in Iowa. Beetle trap counts, gathered through a program that the company helped sponsor with the Iowa Soybean Association, have increased through 2015-17. “The figures don’t always mean growers are going to have heavy pressure the following season but it’s an indicator they need to pay attention.
In the western Corn Belt, growers in Minnesota saw Western corn rootworm problems in fields that hadn’t been rotated for awhile, says Bruce Potter, Integrated Pest Management Specialist with the University of Minnesota.
“We still have the resistance issue with Cry3Bb1 trait — and might as well say is not working. There is some cross resistance to other traits and pyramids as well, but that’s only in specific fields.
“Northern corn rootworm populations were down in 2017, as Western corn rootworm populations had been knocked back after the tough winter a few years back, but they’ve been increasing over the last three seasons,” he says.
Bob Hooten, FMC Technical Expert, would suggest the industry use common sense and throw everything, including the kitchen sink, at the rootworms. “Let’s not allow them to develop resistance. Let’s use a pyramid stacked corn, so it has two different genetic events, then use an insecticide on top of that to at least slow down as much of the resistance as possible,” he says.
For corn in 2018, AMVAC is launching a new liquid at-plant insecticide called Index, containing both bifenthrin and an organophosphate.
“Where growers are seeing heavier corn rootworm pressure, bifenthrin-only solutions haven’t held up as well,” he says AMVAC’s Lappin. One issue: The compound is pretty much immobile in soils.
Organophosphates are more soluble and can move with water up and down the soil profile. “So you get a little larger zone of protection around that early root mass,” he says. With both modes of action, Lappin would describe the Index’s activity as granular level of performance in a liquid format.
This year Syngenta is offering a new liquid formulation of its corn rootworm insecticide Force (tefluthrin), called Force Evo. As a liquid, it offers better cold tolerance and freeze-thaw performance, better starter fertilizer compatibility and easier equipment cleanout, says John Koenig, Insecticide Technical Product Lead.
Syngenta has partnered with John Deere and Raven, both of which make a closed, direct-injection liquid application system to apply Force Evo.
FMC recently received registration for the use of Steward EC insecticide (indoxacarb, formerly from DuPont) in field corn. Target pest here is Western corn rootworm adults.
“Unlike some other chemistries, Steward doesn’t flare mites, which are very difficult and expensive to control. Plus, it provides two weeks of residual control of the beetles, which is also unique,” says Sally Feeley, Insecticide Product Manager with FMC.
As in many parts of the Midwest, soybean aphids are still the number one soybean pest every year in Minnesota, says Potter. The state found some populations resistant to pyrethroids, and the problem seems to be spreading. “We saw it initially in the southwest part of the state in 2015, and this year it was up into North Dakota, South Dakota, and Manitoba,” says Potter. “That’s going to make managing it a little more difficult.”
The industry is “kind of short on products” to manage the aphids with and to rotate, he notes. Control of pyrethroid resistant aphids is currently limited to two other insecticide groups. Growers are using chlorpyrifos and pyrethroid mixes with organophosphates and neonicotinoids.
Chlorpyrifos dodged a bullet in March 2017 when EPA Administrator Scott Pruitt denied a petition to ban it. In 2015, the Obama Administration had announced a proposal to revoke U.S. food tolerances for chlorpyrifos. But EPA’s own Scientific Advisory Panel, along with USDA and other experts, voiced concern that the agency was attempting to regulate chlorpyrifos based on a single unreplicated and unvalidated epidemiology study.
Potter and many other stakeholders are still concerned that all organophoshates, not just chlorpyrifos, are “on the bubble,” as are all the pyrethroids. Neonicotinoids continue to be targeted, too, he says, particularly because of ongoing concerns about their impact on bee populations.
Beyond soybean aphids in the North, the soybean looper was a problem on southern crops for the fourth consecutive year in 2017, reports Syngenta’s Koenig. “This caterpillar is a voracious feeder. High populations can completely strip the soybean foliage from fields, and significantly reduce yield,” he says. “It tends to stay low in the canopy, on leaf undersides. And historically, this looper has been difficult to control since many populations have at least some reduced susceptibility to pyrethroid insecticides.”
Bollworm moths and eggs were abundant in cotton in 2017, and universities have reported more bollworms came through Bt cotton than ever before, says FMC’s Feeley.
One contributor: The warmer weather earlier in the year. Insects will feed on corn as well as cotton — and have a chance to develop on both of those crops, says Hector Portillo, FMC Product Development Manager.
Feeley says Prevathon (chlorantraniliprole (rynaxypyr)), one of the legacy products FMC recently acquired from DuPont, was an important tool to help here.
“It gives growers more freedom to select cotton varieties that are best for their land,” she adds. “By protecting the genetic potential of the crop, they can yield 50 to even 300 pounds greater lint per acre.”
In the West, aphid pressure in cotton came on earlier and stronger than normal this year, which was then followed by whitefly problems, reports California-based Leigh Ann Harrison, Technical Service Representative with BASF.
To help, the company is bringing a new mode of action insecticide to the market in 2019, which combats both of these cotton pests and the growing concern of sticky cotton — as well as many aphids. “We will be sharing more information about this exciting development soon,” offers Harrison.
New Broad Controls
In 2018, HELM Agro US will offer two insecticides, Kendo EC (lambda-cyhalothrin 13.1%) and Diflumax 2L (diflubenzuron).
Bettner says Kendo EC is a versatile tool against the worst economically damaging insects on both row crops and specialty crops. “It’s an advanced third generation pyrethroid with relatively low application rates and a best in class EC formulation. It’s also one of the most competitive and cost-effective pyrethroids on the market today,” Bettner contends.
Diflumax 2L, which can be used on a wide range of row crops, specialty crops and orchard crops is an insect growth regulator (chitin inhibitor) with long residual activity and versatile rates and use timing. According to Bettner, Diflumax is an ideal resistance management product which is ‘easy’ on beneficial insects and pollinators.
“We are excited about the upcoming season,” Bettner says. “Both Kendo EC and Diflumax performed extremely well in 2017. Everything that went out last season exceeded grower expectations in performance and economic value.”
Helena Chemical Co.’s new foliar insecticide, Sultrus, controls insects across a broader range of crops than pyrethroids currently available, says Mark Wayland, Brand Manager, EPA Products. Sultrus is a petroleum solvent-free liquid formulation of beta-cyfluthrin. While providing fast knockdown and long residual control over a large spectrum of insects, it also helps lower the risk of crop injury, particularly when mixed with other crop protection products.
“It offers growers the flexibility to protect over 240 crops from more than 215 insects with short re-entry and pre-harvest intervals,” he adds.
Sultrus has a co-formulated adjuvant system, which enhances spray application coverage and increases adhesion to plant surfaces. And as a spray mix partner, Sultrus is highly compatible with pesticides and foliar fertilizers, Wayland says.
More Bt Stacking
While Monsanto is not offering any new insecticides this year, the company is introducing a new aboveground Bt hybrid, Trecepta. It builds upon the company’s VT2P trait (Cry1A.105 and Cry2Ab2), and stacks that with a third mode of action provided by the Vip3A Bt protein.
The new Bt stack offers control of pests such as corn earworm, Southwestern corn borer and fall armyworm, plus bumps up protection against Western bean cutworm — which continues to be an emerging pest in some corn growing regions, including the Great Lakes and the western Great Plains, says Sean Evans, Corn Technology Development Manager.
He says Monsanto did large-scale strip trials with growers in 2017 throughout the mid-South and into the Southeast. One benefit that emerged is cleaner grain — and more accrued value — due to less ear feeding.
Initial Trecepta release will be in Southern markets, with Midwest availability coming after 2018.
By 2020, Monsanto is looking to release a new product targeted against corn rootworm, called SmartStax PRO. In addition to the two SmartStax corn rootworm-active toxins (Cry1A.105 and Cry2Ab2), it will contain a third mode of action utilizing RNA interference (RNAi) technology. “It’s a completely new mode of action and will help provide more consistent control of corn rootworm — and we also think it’s going to lend a lot to the durability of the current Bt platform,” says Evans.
SmartStax PRO received U.S. registration last summer and is now awaiting all state approvals as well as import/export approvals.
One field taking off is products that allow insecticides to be mixed with other categories such as fertilizer and fungicides.
“We are seeing greater use of a combined insecticide technologies tank mixed with foliar nutrients to manage insect resistance and help recovery from feeding, says Ed Corrigan, Agronomy Manager with BRANDT. “We are also seeing higher volumes sprayed per acre and the use of buffering agents for improved control.”
He recommends products such as BRANDT Smart B and/or BRANDT Smart Quatro for foliar nutrients in insecticide tank mixes. The nutrition boosts plant health, mitigates plant stress from heat and insects, and also buffers the tank mix solution for improved insect control, he says.
By the end of 2018, FMC will be labeling a new fungicide/insecticide combination for use in the company’s exclusive 3RIVE 3D expanding foam delivery system, introduced in 2015. With it, growers can use ultra-low volumes of finished solutions, while still getting the coverage needed, says Bob Hooten, Technical Expert with FMC. He views it as a breakthrough in ag: a new delivery system “that really saves time, labor, weight — all of the things a user is looking for,” he says.
The new 3RIVE 3D application system uses patented formulation and application technology to precisely deliver the broad spectrum insect protection that growers need and is available free to growers if they sign up for the qualifying amount of FMC products.
Timing is crucial for this kind of dual pest control. Purdue’s Obermeyer said growers battling western bean cutworm last season did try applying insecticides with their fungicide, which typically goes on at the late R1, R2 growth stage. “Guys were wanting to try and hold off the insecticides until that stage, but it was too late to get the insecticide on,” he says.
A possible solution would be to put the fungicide/insecticide combination on before tassel.
Pest Predictions for 2018
“The kind of weather we get over the next several months will indicate the corn rootworm egg survival rate will be going into the spring,” says AMVAC’s Lappin. Beetles have laid their eggs in the soil, and they tend to move down to moisture, so in dryer areas they will be deeper in the soil profile. In wetter areas they will stay near the surface.
HELM’s Bettner says growers should expect more insect pressure in 2018, especially if the winter months are “soft.” Beyond corn rootworm, western bean cutworm and corn earworm, pests to watch include soybean aphids, bean leaf beetles, Japanese beetles and spider mites. “Growers will also be on high alert for stinkbug populations not only in the South but in pocket areas of the Midwest,” he adds.
Insect numbers will be on the rise as dry soil conditions continue to dominate in many areas, says BRANDT’s Corrigan. There will be increased “hot spots” of rootworms where less rootworm traits are used and where there are late planted fields that become “trap crops” for the insects to lay eggs in.