Emily Zobel, Agriculture Agent Associate
University of Maryland Extension, Dorchester County
Overwintering bean leaf beetles are emerging and starting to feed. Soybean seedlings can recover, with no yield loss, from 40% defoliation. Many small caterpillars, such as the green clover worms will also defoliate plants. However, once soybean plants start to bloom, you want to control defoliating insects when you have greater than 15% defoliation.
Check for cutworm and armyworms leaf feeding on young corn plants. The threshold for cutworms is when 10% of the field has feeding damage at 1-2 leaf, and 5% damage at 3-4 leaf or 4 larvae found per 100 ft. For armyworms, the treatment threshold is when 25% of the plants are infested and larvae are under a 0.75 inch long. Armyworms that are 1.25 inches are late instars and have likely completed their feeding.
No-till fields of both corn and soybean are at an increased risk of slug damage. Slugs feed at night, so you will likely not find them during daytime scouting. Their feeding damage will be found on the lower leaves of plants. The leaf will have narrow, irregular, linear tracks or scars of various lengths that may be eaten partly or entirely through the leaf. Peter Coffey wrote a great article about slug management, which can be found here (https://blog.umd.edu/agronomynews/2018/05/03/what-should-i-do-about-slugs/) .
As wheat gets harvested during the month, stink bugs may move into nearby cornfields. Their feeding could affect the developing ear and kernels. Populations will be highest around the edge of the field, and full-field control may not be needed. Field corn treatment threshold are when 25% of plants are infested with stink bugs before pollination, and 50% of plants are infested with stink bugs are after pollination up to early dough stage. Counts should be done on 10 plants in 10 different locations in the field. Do not count beneficial stinkbugs, such as the spined soldier bug.
