July IPM Insect Scouting Tips
Be sure to check all labels carefully before applying and combining insecticides and herbicides.
Scout for the usual defoliators, including bean leaf beetle, Japanese beetle, and caterpillars. The treatment threshold is 15-20% defoliation for bloom to pod fill. Note that defoliation percentages should be based on the entire soybean plant or canopy, not just the top leaves or worst leaves. University of Nebraska Extension has a nice guide for defoliating insects in soybeans (https://croptechcafe.org/defoliating-insects-in-soybeans-thresholds-training-and-tools/).
Adult Dectes Stem Borer will be emerging over the next several weeks. Chemical control is not recommended since it would require multiple applications to reduce larval infestations, which is not economical. However, if a high number of adults are found, harvesting that field as soon as it matures will reduce losses associated with lodged plants.
At the start of silking, scout for Japanese beetles and stink bugs. For Japanese beetles, the treatment threshold is when there is less than ½ inch of silk and less than 50% pollination, and an average of 2 or more beetles per ear. For stink bugs, the threshold is 1 bug per 10 plants (V1 to V6), 1 bug per 8 plants (V14 to VT), and 1 bug per 4 plants (R1 to R2). Stink bugs and Japanese beetles are ‘edge’ pests, so treatment may only be needed around field edges and pivot tracks.
Continue scouting for potato leafhoppers (PLH). Cutting will destroy many of the nymphs, and adults will often move elsewhere, but be sure to scout the regrowth. A rough threshold estimate is 20 PLH per 100 sweeps on alfalfa 3 inches or less in height, 50 PLH per 100 sweeps in 4-6 inch tall alfalfa, and 100 PLH per 100 sweeps in 7-11 inch tall alfalfa. A more precise threshold chart can be found on the Penn State Extension website https://extension.psu.edu/potato-leafhopper-on-alfalfa.
This article appears on July 2021, Volume 12, Issue 4 of the Agronomy news.