Updated: June 6, 2024
By Emily Zobel


June 2024


Continue scouting for cutworms and stink bugs. The threshold for cutworms is 2-5% cut plants up to the V5 stage and with active larvae present. Stinkbugs will move into corn as surrounding small grains are harvested. When scouting for stinkbugs, pay close attention to the thorax of brown color stink bugs as the beneficial spined soldier bug is often mistaken for the invasive brown marmorated stink bug. The spined soldier bug has a prominent spine on each "shoulder." NCSU's suggested threshold is 13 stinkbugs per 100 plants for V1-V6, 10 stinkbugs per 100 plants for V14-VT, and 28 stinkbugs per 100 plants for R1-R2. The most critical time to treat if between V14 to VT is just before the primary ear is exposed to avoid banana ear. Stinkbugs will likely be around the primary ear at this point so that should be the target of the application.


Bean leaf beetle
Figure 1. Bean leaf beetle with feeding damage on a soybean leaf. Photo by Adam Sisson, Iowa State University, Bugwood.org.

Early-season defoliator pests that are active right now include bean leaf beetles, green cloverworms, slugs, and grasshoppers. Soybeans can typically withstand a decent amount of defoliation before yield losses occur. If defoliation reaches 30%, and you are finding one grasshopper per sweep or 2-3 bean leaf beetles per plant treatment may be advisable.


Potato leafhoppers
Figure 2. Potato leafhoppers in a sweep net. Photo by Bryan Jensen, University of Wisconsin, Bugwood.org.

Begin scouting for potato leafhopper. Ten sets of 10-20 sweeps using a sweep net should be taken in random locations in the field. A detail threshold for alfalfa is based on the plant size and cost of the hay can be found online but a general guideline is 3” or less is 20 leafhoppers per 100 sweeps, 4-6” tall is 50 per 100 sweeps, 7-10” tall is 100 per 100 sweeps, and greater than 11” is 150 per 100 sweeps. If the field is more than 60 percent bud stage or if it has experienced “hopper burn,” the alfalfa should be cut instead of sprayed. Fresh-cut alfalfa should not be sprayed as leafhopper adults tend to move out of the field when it is being cut.

Agronomy News is a statewide newsletter for farmers, consultants, researchers, and educators interested in grain and row crop forage production systems. This newsletter is published once a month during the growing season and will include topics pertinent to agronomic crop production. Subscribers will receive an email with the latest edition.