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New options for pest control

Plan ahead and use rotation to minimize resistance development.


March 11, 2008
By Donna Fleury

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As new chemistries and modes of action become available, it is critical that the industry use good management strategies to reduce the risk of resistance. Some of the currently available products have resistance problems, so the industry must use best practices to keep as many tools available as they can.

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European corn borer larvae feeding on potato.

Dr. Galen Dively, Professor Emeritus at the University of Maryland, explains there are currently two main classes of insecticides available for potatoes. The neonicotinoids class, which includes products such as Admire, Assail and Actara (Platinum is registered in the US), are available as systemic products or foliar formulations. “Admire was registered in the US in 1995 and we’re already starting to see resistance to that class of chemistry in both the US and Canada,” explains Dively. The active ingredient is imidacloprid.

In Maine, Delaware and several states, the level of resistance is quite high. “I completed bioassays of about six populations in Canada this year and two are definitely showing tolerance,” says Dively. Another product, Success (called Spintor in the US), with the active ingredient spinosad, offers an alternate mode of action.

DuPont Canada is working with the PMRA to have a new insecticide registered in 2008. “Rynaxypyr, which is to be marketed under the name Coragen in potatoes, is from a completely new family of chemistry,” explains Adam Vaughan, product registration manager, DuPont Canada. “It is the first active ingredient from the anthranilic diamide class of insecticides and offers a novel mode of action.” Research is showing this unique molecule is effective at providing long-lasting control of a broad spectrum of chewing insects and several other important insect species at low application rates in a wide variety of crops. Coragen is a foliar application product.

Rotating pesticide groups and modes of action is very important. “When the new Rynaxypyr chemistry becomes available, growers will have at least three modes of action to use in rotation, plus some older chemistries that may work,” explains Dively. Growers are reminded that new products or new formulations are not necessarily new modes of action. For example, a new generic imidacloprid, the same active ingredient and mode of action as Admire, was registered recently as Alias 240 EC. Therefore, it is important to understand all of the details about a new product or formulation so proper resistance strategies can be followed.

Since Rynaxypyr is from a completely new family of chemistry, it has no cross-resistance with existing products. “Managing new and existing chemistry involves rotating the use of products with different modes of action,” says Vaughan. “A good resistance management strategy is based on rotation of different modes of action and not rotation of different products with the same or similar mode of action.” History tells us that cross-resistance can quickly develop between products with the same mode of action. “Large scale research permit field trials conducted in 2007 from Manitoba to Prince Edward Island have shown Rynaxypyr to be a useful tool in resistance management,” he adds.

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Left side of the picture shows untreated potatoes with significant defoliation from Colorado potato beetle feeding. Right side of the picture shows protection provided by 75 grams active ingredient per hectare rate of Rynaxypyr. Photos Courtesy Of DuPont Canada.

One of the other key tactics for delaying resistance is to follow good crop rotations. “Where possible, moving potato fields at least a half kilometre away from last year’s crop is a good idea,” explains Dively. Adult beetles do not move very far, so any beetles that survived a pesticide regime and have possibly selected for resistance will likely overwinter just outside the field. “By moving the new crop farther away, it reduces the chances that any resistance can be passed on to the new population in the new location. In popular potato growing areas and for some growers, this can be a challenge.

Growers are encouraged to monitor populations and follow economic thresholds. Wait, scout and monitor before making a decision to use a pesticide. “Potatoes can actually tolerate a lot more damage than what most growers think they can,” says Dively. “There has been quite a bit of research, particularly on early adult feeding damage, and we’re realizing it’s not as bad as we always thought.” So do not use pesticides if it is not necessary. The more the crop is treated, the more selection pressure and the greater the chance of driving that insect to resistance.

“Consider whether or not you need to use a pre-plant systemic insecticide at planting,” explains Dively. In many situations, a pre-plant application may not be necessary. “One of the strategies some of the potato growers in the US mid Atlantic areas are doing for planting treatments is to just treat the outer perimeter of the field, leaving about 70 percent of the acreage in the middle untreated.” When the beetles come out from overwintering, they are usually quite weak and tend to walk into a field rather than fly. Therefore, if the outside perimeter of even 100 feet is treated, this treated barrier will kill the adults before they get into the rest of the field. That means a savings of 70 percent of the costs and provides a central refuge for the few that do survive. Leaving a refuge for some bugs to survive helps delay resistance.

If a pre-plant systemic product was used at planting, then use a different mode of action for any in-crop applications. For in-crop control, monitor and wait for the first generation of larvae to hatch and exceed economic thresholds, and then use a product like Success. Dively says, “If you need to use another foliar application, there will be two modes of action once Coragen becomes available.” Never repeat a treatment because adequate control was not obtained. This is the first sign that resistance is high. Always change chemical groups if repeated treatments are necessary.

Planning ahead and keeping new chemistries away from the risk of resistance as long as possible is important. “Follow good crop rotations, use good agronomics and IPM strategies to keep the crop as healthy and competitive as possible and always follow good chemistry and mode of action rotations,” says Dively. “Rynaxypyr is going to have a good fit for potato growers with its new chemistry and new mode of action, helping to address pest control resistance issues.” -end-

Another product for CPB

Rynaxypyr is the first product to be simultaneously reviewed by Canada, the US, Europe and Australia under an Organization for Economic Co-operation and Development (OECD) work-sharing project, according to DuPont. The project is aimed at an accelerated review and approval timeline and regulatory harmonization. This process ensures that Canadian growers have access to the same products, for the same crops as growers in the US and other countries. It also ensures that Maximum Residue Levels (MRL) are established at the same time in as many countries as possible. The application for international CODEX MRL has also been accepted
for review.

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Craig Hunter, technical advisor,
pesticide and minor use issues, OFVGA.
Photo Courtesy Of Iden Ford Photography Toronto.

“We take our hats off to DuPont for taking a real global leadership role with this registration approach,” says Craig Hunter, technical advisor, pesticides and minor use, Ontario Fruit and Vegetable Growers’ Association (OFVGA). “They are really a ‘poster child’ of how growers would like to see companies approach new registrations. We hope other companies follow their lead.” Having the product registered globally at the same time ensures growers are facing the same residue tolerances in all countries, and trade is therefore not an issue in terms of pesticide use.

With an entirely new chemistry and novel mode of action, Rynaxypyr will expand the range of tools growers have to address pest problems and the potential of resistance. “We’ve already lost some products over the past few years because of resistance, or voluntary elimination in the face of the US FQPA review program, and other standbys such as Guthion are slated to be taken off the market in 2012,” says Hunter. “Therefore, it is exciting to see some new chemistries being brought in that will have spectrums of activity that will eliminate or greatly reduce the impact of losing these old standbys we’ve relied on for years.”

Rynaxypyr was accepted for review under the reduced risk category. It is applied at low use rates and has a unique mode of action. The many regulatory studies conducted over the past few years demonstrate the effectiveness and extraordinarily low toxicity of Rynaxypyr to mammals, birds and fish. The product also achieves the goal of delivering safe and environmentally sustainable options for growers. -end-