Your Garden … with Kate Russell – Brown marmorated stink bugs have invaded South County

Published in the October 31 – November 13, 2018 issue of Gilroy Life

A brown marmorated stink bug. Image courtesy Wikipedia.

The brown marmorated stink bugs have invaded Gilroy and Morgan Hill. Well, maybe not invaded, but these invasive pests can be serious garden pests.

Most stink bug species eat popular crops, including corn, tomatoes, nut and fruit trees, beans, peas, peppers, berries, grapes, and cucumbers. Stink bugs inject plants with enzymes that makes the fruit brown and tough. This sets the stage for bacterial, viral, and fungal diseases. Stink bugs also feed on buds, flowers, leaves, stems, and new bark, and they like to overwinter in your house. So, what makes brown marmorated stink bugs worse than other stink bugs?

Brown marmorated stink bugs are originally from Eastern Asia. They appeared on the East Coast in 2001. By 2004, they had reached the West Coast. They are now found in more than 40 states. While beneficial predators control native stink bug populations, this pest has few natural enemies and chemical insecticides are ineffective.

Adult brown marmorated stink bugs are 5/8-inches long and mottled brown. Like other stink bugs, they have a shield-shaped body. These particular stink bugs feature two white bands on their antennae, a blunt face, faint white bands on the legs, and a banded edge around the abdomen.

Barrel-shaped eggs are white to pale green, and are normally laid in clusters on the underside of leaves. After hatching, nymphs go through five developmental stages, or instars, that change from dark brown with orange markings to the mottled brown of adulthood. Nymphs are commonly seen next to egg clusters.

Each autumn, these pests gather along fences, tree trunks, and buildings. Then they move to protected areas to overwinter in a resting stage called “facultative diapause.” In spring, adults become active again and start feeding. Within two weeks, they mate. Soon after, each female will lay 200 to 500 eggs. In the Mid-Atlantic, there are two generations each year. Here in Gilroy, there will probably be more than two.

Since insecticides don’t work, and there are few natural predators, what is a gardener to do about brown marmorated stink bugs? First, exclude them from your home using caulk and weather-stripping. Next, turn off unnecessary lights at night. Assassin bugs, green lacewing larvae, some parasitic wasps, and earwigs are known to feed on stink bugs, so avoid using broad spectrum insecticides. Row covers can also be used. Heavy infestations can be addressed with a shop vacuum. The most effective stink bug control is simply handpicking.

Kate Russell is a UCCE Master Gardener in Santa Clara County. For more information, visit mgsantaclara.ucanr.edu or call (408) 282-3105 between 9:30 a.m. and 12:30 p.m., Monday through Friday.