NORTH PLATTE, Neb. — Insects are causing problems for alfalfa across Nebraska. Stay tuned as I describe what to look for in your fields and what to do if an issue does arise.
From alfalfa weevil larvae and adults to potato leafhoppers, to army worms, cutworms, alfalfa caterpillars to all kinds of aphids, somebody, somewhere has had enough of each of these insects feeding on their alfalfa, damaging new seedlings or regrowth. If you have been lucky enough to avoid these pests thus far, don’t assume you are safe for the remainder of the year.
Be sure to get out and scout your fields. I’d love to be able to generalize and tell you exactly how many insects per square foot or sweep of a net is needed to economically justify a control treatment for alfalfa. But each insect and disease are different. It can range from one spotted alfalfa aphid per seedling to 100 pea aphids on 20-inch alfalfa. Or from one or two armyworms per square foot in new stands to at least 10 alfalfa caterpillars per sweep in established stands. Not all diseases cause issues.
What we use for control also varies. Simply cutting often works for many soft bodied insects. Control using natural organisms like the Bt in Dipel and Thuricide will work for some insects. And of course, insecticides. But what insecticide or fungicide to use will be different depending on the insect.
So, my take home message today is scout and identify what is plaguing your field. Look for slow regrowth or weak seedlings and scout for insects or diseases that might be causing the issue. Be sure to dig in the soil and dead litter to find insects hiding during the day. Then identify exactly what you are dealing with. If you need help, stop in at your county extension office. Remember, many insects you find will be beneficial and some diseases don’t cause yield issues.
And finally, use appropriate treatments to protect your alfalfa.
— Melissa Bartels, Nebraska Extension
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