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Pay Attention to Alfalfa Insects This Spring

alfalfa weevil
Insecticides are available to control alfalfa pests.

Maybe you grow alfalfa for a living. Maybe you only have a field or two for your own livestock. Whatever the case, now is the time to be checking for insects so that you don't sacrifice yield and quality to these pests, including alfalfa weevil and potato leafhopper.

That's the message from Mark Lawson, a farmer and technical agronomist for Syngenta. He's based near Danville. While he doesn't raise alfalfa himself, he sometimes gets questions about how to protect the crop from pests.

Inspect alfalfa: Now is the time to check for insects and make decisions about spraying or taking the crop off early if insects are reaching the economic threshold. (Purdue photo)

The first thing is to know that the pest is there, Lawson notes. That requires scouting. One method involves using sweep nets. Purdue University Extension educators should be able to hook you up with more specific information about how to look for the various pests, how to identify and quantify them and how to make decisions about when it would pay to treat the pest. It can vary depending upon level of the infestation plus stage of growth of the insect and the crop. If the crop is close to maturity, one remedy is to harvest it and then be ready for pests in the next cutting. This depends on if the weather cooperates, and what capabilities you have to harvest the crop as perhaps baleage, or if you have to wait and make dry hay, which could take longer with current weather patterns.

The product in Syngenta's line that can control weevils and potato leafhopper is Warrior II with Zeon Technology. Whatever product you use, Lawson says it's important to carefully study the label, not just glance at it.

For example, the Warrior II label gives specific instructions about when to treat for alfalfa weevil. The label says to treat when 40% or more plant stems show recent tip-feeding and the average is three or more larvae per stem. Compare this against Extension recommendations. It also gives very specific rates to the one-hundredth of an ounce. The label also lists crops the product is approved for, and which pests it will control.

Going to the field to spray without checking the label is going out blind. Lawson strongly suggests you follow the label.


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