Air April 9, 2003

Thank you Gary, and good morning everyone. I love April weather! Up down and all around, but at least we received some precipitation out of it all.

With temperatures in the high 80s for several days last week, it should come as no surprise to anyone that the alfalfa weevil started hatching and feeding. By late week I was finding weevil larvae that were anywhere in size from half grown to just hatched. Now, while there was certainly some obvious feeding going on, we don’t want to be in too big of a hurry to spray. If the weather had stayed in the 80s over the weekend, there would have been some concern, but this colder weather has worked to our benefit. No, they haven’t all been killed by the cold weather, although a few may have perished - but the colder the weather the slower they eat and the slower they develop. We should be back into the 70’s the rest of the week and into the weekend so that will get the little rascals cranked back up. Therefore it would be prudent to start checking your fields every couple of days. We have to remember that we don’t spray as soon as we see a pest. We want to wait until the damage that they are about to do is going to cost us more than the treatment. This economic threshold is different for every pest and every crop, and in the case of alfalfa even changes with the value of the crop. Given the current value of first cutting alfalfa, we probably need somewhere from 1 to 2 larvae per stem to justify treating. Obviously we want to hold off as long as possible so that we only need to treat once on the first cutting. Early in the season we know that there are still more weevil eggs to hatch. Unfortunately, though, if we wait too long, alfalfa weevil can not only damage the current cutting, but they can cause residual effect that will reduce production the entire rest of the season. IF we decide we need to spray, we next are faced with a myriad of insecticides. So we need to look at how many days of protection a product gives us and then later on we need to look at how long until we can harvest. In reality we can’t expect more than about 14 days of protection from even the strongest products, and less on others. We don’t really have many new products this year to choose from. But the first step is to get out there and scout your own fields! Call me if you need some help!

This is Chuck Otte, Geary County Extension Agent, with Ag Outlook 2003.

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