Potato Grower

May 2014

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www.potatogrower.com 39 and more valuable, and their efficiency should not be squandered due to a less- than-optimal use. The most basic principle of insecticide resistance management is not relying on repeated applications of the same, or closely related, chemicals for pest management. Otherwise, a single mutation may mean control failure in the field. To the contrary, using a multiple- attack strategy would require that the beetles undergo profound genetic changes to become simultaneously adapted to multiple unrelated factors. Such changes are significantly less likely to occur than a one-gene mutation. Therefore, practicing integrated pest management is by far the best approach to delaying the evolution of resistance. In practical terms, this means doing the following: Not following an insecticide with any other insecticides that have similar chemistry within the same season. Doing so will ensure the most favorable conditions for resistant beetles because all their competitors for food and mates will be dead. The Insecticide Resistance Action Committee, an industry group working on managing resistance, separates all insecticides into groups based on their mode of action (basically, on how they kill their target pests). Some of the groups are further divided into subgroups. Most insecticide labels have this information on the first page. The best approach is to rotate insecticides from different groups. If this is absolutely impossible, rotating insecticides from different subgroups is also acceptable, but somewhat more risky. Insecticides from the same subgroup (or the same group that is not divided into subgroups) should not follow each other. Not relying on insecticides alone. Whenever possible, chemical control should be supplemented with other management techniques. In particular, crop rotation has been repeatedly shown to suppress Colorado potato beetle populations. Rotated fields should be separated as much as possible both in time (number of years between successive potato crops) and space (separation between previous and current year crops). Using economic thresholds when making decisions about spraying. Not only does excessive spraying result in a waste of time and money, it also contributes to rapid resistance development. Trying to kill all the beetles with insecticides usually results in killing all susceptible beetles. Only resistant beetles survive. (That's exactly what makes them resistant on the first place). When resistant beetles mate with each other, all their progeny are resistant. When resistant beetles mate with susceptible beetles, their progeny is less resistant and usually can be killed by the full label rate of insecticide. The same applies to treating areas of elevated beetle activity within a field instead of treating the entire field. Using full label rates of insecticides. Otherwise, the hybrids between resistant and susceptible beetles will not be killed. Because of the way insecticide resistance is inherited at the gene level, some of these hybrids may produce highly resistant offspring. Necessary steps should be taken before insecticide failure becomes noticeable in the field. Preventing resistance is as essential a part of good insecticide stewardship as minimizing drift or wearing personal protective equipment. PG Dr. Andrei Alyokhin is an associate professor of applied entomology at the University of Maine. The primary focus of his research has been on insects affecting potatoes. Custom Saddle Tanks For Your Tractor 522 Lincoln • American Falls, Idaho • 208-226-2555 1801 South 2800 West • Aberdeen, Idaho • 208-397-5300 C h e C k F o r n e W, C u S to m o r u S e d e q u I p m e n t At W W W.d o u b L e m S u p p Ly.C o m KEEP BUGS OFF YOUR BOTTOM LINE Double M for your chemigation needs!

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