April 2007
Managing for control of Colorado potato beetle

As usual, the beetle is battling back.

Potato growers are unique among all farmers in having to contend with the crown prince of insect pests, the Colorado potato beetle (CPB). It thrives on plants of the nightshade family. It is well adapted to natural toxins. It knows how to marshal its internal mechanisms to detoxify synthetic chemicals as well. The litany of its triumphs over a host of insecticides the past four decades reads like a lamentation.

And now it is showing signs of neutralizing the neonicotinoids. This class of insecticides evoked fervent grower gratitude when it was introduced a dozen years ago. For some it saved their businesses. But the early punch against the potato beetle is starting to wear off.

Resisting the increasing insecticide resistance of CPB is a complex task but extremely necessary, said new National Potato Council (NPC) President Don Sklarczyk of Johannesburg, Mich. He has been wary of CPB resistance to neonicotinoids since the beginning. In his five years as NPC’s vice president of environmental affairs, he preached the message of prudent pesticide use for the cause of extending neonicotinoid effectiveness indefinitely if possible.
EPA agrees with Sklarczyk. NPC’s productive dialogues with regulators continue the relationship formalized in 1988 with the joint NPC/EPA Pesticide Environmental Stewardship Partnership (PESP), which focuses on pesticide risk reduction in potato production and also triggered NPC’s annual Environmental Stewardship Awards (ESA). Sklarczyk believes resistance management underscores the point that sound stewardship is integral to sound business practice.

Unfortunately, despite many growers’ best efforts, CPB is making headway in its ceaseless quest for survival. Resistance is already extensive on Long Island, where the insect seems to welcome each new insecticide as a kind of fine wine for finishing off a gourmet dinner. Elsewhere the results vary, according to testing last year at the Vegetable Entomology Laboratory at Michigan State University for imidacloprid (Admire Pro, Provado) and thiamethoxam (Platinum, Actara). Beetle samples came in from as far away as Maine and Washington.

Specimens from some Massachusetts and Delaware fields and one Maine location were already far above desired resistance levels for imidacloprid. One Delaware sampling was in the same category for thiamethoxam as well. Minnesota, Wisconsin and Washington fared better, although in some cases the dose rate for killing half the population was significantly” above that of a susceptible CPB strain. The warning signs were becoming apparent.

The Michigan results also showed a sharp range from well under control to red-flag status. The highest readings make for something of a mystery, said Ed Grafius, MSU emeritus entomologist, who has been a warrior against CPB for three decades. Most were in Mecosta County, a satellite of the major Michigan potato region in Montcalm County. Growers in Mecosta County have followed similar practices as others in the state where resistance is still low, yet the Mecosta beetles have displayed much stronger detoxifying power.

Some populations seem to have a greater mutation ability, Grafius said. The early CPB history in the United States was that the insects did not even like potatoes. In southern Texas and northern Mexico they fed on buffalo bur, and in that region today, he said, they reject potatoes despite being genuine CPBs. As the insects came north, probably on the flanks of livestock during cattle drives, some populations found potatoes and mutated into critters that have made that crop their primary menu choice ever since. It’s possible, Grafius said, that CPB genetics in the somewhat isolated growing region of Mecosta County resulted in localized advanced resistance.

Among the operations there is Sackett Potatoes of Mecosta, Mich., a part of the extended Sackett family with a century-long potato history in Michigan. Twenty years ago, Alan Sackett left Montcalm County when his sons Jeff and Brian were old enough to join him in a new venture, which began with 1,200 leased acres they subsequently bought. They now grow 5,200 acres of irrigated crops, half in potatoes plus 2,000 acres in field and seed corn and 500 in peas. The quality of their farming has led to numerous honors. They are past ESA winners and have been named “Champions” in the EPA’s PESP program. In December, Sackett Potatoes received the designation of 2006 Master Farmer of the Year by the Michigan Vegetable Council, awarded at the Great Lakes Fruit, Vegetable and Farm Market EXPO in Grand Rapids, Mich.

Last summer, the operation was a major stop on the annual Michigan tour for government officials sponsored by the Michigan IPM (Integrated Pest Management) Alliance, an organization of commodity groups including the Michigan Potato Industry Commission that promotes IPM practices. Among the guests was Thomas Brennan, now chief of EPA’s Environmental Stewardship Branch, who got a front-line look at the potency of the CPB adversary.

The Sacketts, working with their crop consultant Mark Otto, president of Agri-Business Consultants of Lansing, Mich., have had a resistance-prevention program in place for many years.
Rotations have always been central in their strategy.

“There’s major mortality when Colorado potato beetles are forced to move more than a quarter of a mile from this year’s potato fields to the next year’s potatoes,” Otto said. “The greater the distance, the longer it takes for significant numbers to find the new field.”

The beetles don’t walk beyond about 400 yards, Grafius said. Although they can fly 10 miles or more, their flight plans in search of distant fields are scattershot, and most don’t make it.
“The numbers will be much lower than in fields with continuous potatoes or fields that are rotated side-by-side or across a road or fence row,” he said.

Otto takes advantage of CPB’s pedestrian habits to further thwart the pests by planting trap crops.

“This allows us to concentrate beetles and treat them with non-neonicotinoid insecticides. Then we destroy the trap rows before a new generation of beetles can attack our potatoes,” he said.

The policy impressed EPA’s Brennan.

“It’s a well-thought-out microscale strategy,” he said. “Resistance management is not just about pesticides but also cultural practices.”

Unfortunately, a new challenge to rotational strategies has reared itself before Michigan potato growers corn fever. Ethanol plants have been proliferating around the state to the extent that local prices for corn have nearly doubled from long-stagnant levels. More acreage is going into corn, and more owners who rented land are getting back into production themselves. Although some observers think the boom in corn and land prices is headed for a fizzle in a few years, right now the problem is a tight land market.

“Our potato growers are finding it more difficult to rent land,” Otto said.

That tightness forces alternatives to neonicotinoids, but Grafius said the thiamethoxam group is not a good candidate because a great deal of cross-resistance is showing up. The defense mechanisms built up by the beetles against one type of chemical become effective in detoxifying the other type.

“We don’t recommend repeat or back-to-back foliar applications with materials from the same mode of action group,” Otto said. “Whenever appropriate, we use reduced-risk materials such as Agri-Mek, SpinTor and Rimon to conserve natural enemies. And using insecticides only when needed as determined by research-based thresholds reduces selection pressure.”

Those chemicals are available and still effective in Michigan Rimon against larvae Grafius said, adding that a welcome mode of action weapon is on the horizon.

“Registration is expected this winter or spring for Alverde, a new product from BASF Corp., that will also be a good product to rotate with neonicotinoids,” he said.

Otto is hopeful for even more diversity, noting that Bayer CropScience is contemplating getting Temik re-registered on potatoes in Michigan.

“That will help us increase the diversity that we throw at them,” he said.

“This would further help us conserve CPB susceptibility to neonicotinoids. Minimizing or at least reducing insecticide selection pressure is the primary concern of most insecticide resistance-management plans. Our clients generally ascribe to the notion that only growers can prevent insecticide resistance from developing by the management decisions they make.”
Grafius appreciates that attitude.

“It’s ironic, and not immediately logical, but insecticides that are very effective and very widely used are the ones that put the most pressure on the beetle and are often the ones where resistance appears the most quickly,” he said. “Growers should be careful not to repeatedly use neonicotinoids but to alternate with insecticides from other groups that and use crop rotations.”

The historic resiliency of CPB against insecticides gives rise to the horse-and-barn-door analogy.

“Resistance management is most effective if it’s practiced before resistance has even begun to appear,” Grafius said.

He recommended NPC educational bulletins on resistance management addressing not only CPB but aphids, diseases and weeds.

“The National Potato Council is the only grower group I know of that has taken such leadership regarding resistance management,” he said.

Online bulletins can be downloaded through www.nationalpotatocouncil.org. Go to “Press Room” and then “News Flashes.”

Brennan encouraged growers to make a commitment to resistance principles.

“Sackett Potatoes is a good model for this scientific approach,” he said. “I realized during my visit there why they’re past champions in the Pesticide Environmental Stewardship Partnership.”

NPC President Sklarczyk summarized the situation growers face:

“Resistance management is not limited to one practice or one event. Resistance management ties into a stewardship plan for an operation. Without one the other would fail. Operations like the Sacketts’ that recognize the importance of proactive approaches not only benefit their own operation but provide benefits to the whole agricultural community. The benefits go beyond fence rows or crops. Resistance is a community problem and can be best served with everyone understanding the importance of total stewardship of the environment.”

The proactive approach becomes complex within the reality of dynamic agricultural markets and their unintended impacts elsewhere in the rural landscape. But, Sklarczyk stresses, it’s worth it.”

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