Agronomic Crop Insect Scouting

David Owens, Extension Entomologist,

Now that most of the alfalfa has been cut, scout the regrowth for potato leafhopper. Remember, once hopperburn is observed, yield has already been damaged. In our alfalfa recommendations there is a threshold table, similar to that for alfalfa weevil, taking plant height, control cost, and value of the hay into account. Generally, leafhopper abundance needs to be between 20 – 30 for plants less than 8 inches tall, and greater than 60 for taller plants. Pyrethroids work well for leafhopper.

Continue scouting corn for stink bugs. Generally, they are going to be concentrating near the ear-zone, where the ear would emerge. Stink bugs will hide in leaf axils, so a sharp eye is necessary. They also like to flip over to the opposite side of the plant to avoid being seen. North Carolina and Virginia revised threshold guidance last year given research efforts from 2016 onward. You do not need to treat if you have less than 4 bugs per 100 plants, and a treatment is advisable when there are greater than 10 stink bugs per 100 plants. You can find the full threshold table here:

The earliest planted soybean is now in flower. During the reproductive stages, defoliation thresholds decrease to 15-20% defoliation. Make sure that it is ‘new’ defoliation and not old injury. Currently active defoliators include bean leaf beetle, grasshoppers, bean leafroller, thrips, and the occasional spider mite, all generally at low enough levels to not warrant a treatment. For grasshoppers, we did a spray trial last July on a grasshopper population using low to mid-rates of pyrethroids and they did not provide satisfactory control. If treating for grasshopper, use a high label rate or consider using Prevathon or Vantacor (chlorantraniliprole) or a diamide premix like Besiege or Elevest. All three of these chemicals should be mixed with methylated seed oil for grasshopper control, per label guidance.