Alfalfa weevil woes
June 1, 2010
This has already been a difficult year for alfalfa growers. Since we have the most acres of any county in Kansas, we always have to spray for alfalfa weevils because they come every year. Normally we get good insecticidal control. We have had difficulty getting control in 2010.
This is not just a local problem but has been a state-wide phenomena wherever alfalfa is grown. I think entomologists have decided that unusually high insect numbers, combined with cool weather causing slow growth on the alfalfa, allowed the bugs to take advantage. Sometimes the hay grows fast enough to out grow the insect feeding pressure.
There was some fear that there may be some resistance in the population but at this point, after doing some testing they aren’t sure. They do know that at least one of the products which has typically given good, consistent control did not work well this year.
Earlier there was some thought that perhaps we started spraying too early and that they hadn’t all hatched yet and that we shouldn’t be tank mixing products because chlorpyrifos (Lorsban and numerous generics) can only be sprayed once per cutting and if the tank mixed failed you have no rescue treatment.
This is all compounded by the fact that the old stand-by Furadan, has been taken off the market and Malathion and even Sevin have lost their labels for alfalfa weevil.
At this point the alfalfa is ready to cut anyway, weather permitting.