By Julianna Wilson

It took 14 years for the brown marmorated stink bug to reach Michigan from its start in eastern Pennsylvania in 1996. Since 2015, BMSB has been considered a nuisance pest in homes in the southern part of the lower peninsula. In apple and peach orchards, more growers are reporting low levels of stinkbug damage on fruit. There are a few key strategies for monitoring and assessing damage.

Because adult BMSB overwinter in man-made structures, these bugs can become a nuisance pest in homes. Woodlands provide both overwintering shelter and a ready source of non-crop host plants, especially tree of heaven, buckthorn and honeysuckle.

In Michigan, BMSB likely begins laying eggs on the undersides of host plant leaves in late May, and hatch into nymphs in early June. Nymphs and adults can feed on up to 300 different kinds of plants, potentially causing economic damage to fruits, nuts, vegetables, field crops and ornamental plants grown by producers. Visit Michigan State University Extension for more information on the crops and ornamental plants they feed upon.

There is still a lot to learn about the impact of BMSB on Michigan crops throughout the growing season. Research has shown that BMSB are very mobile — moving from woodlands to cropland and among different crops as they mature — throughout the growing season. BMSB also tends to be found along the edges of these habitats, which is important knowledge for crop scouts.

DAMAGE: To assess damage in orchards, collect 100 fruit at random from a block and count the number of fruit with suspected stinkbug damage; this number can be used to generate a percentage of damaged fruit in that block.

For instance, a telltale sign of BMSB feeding in soybean fields is delayed ripening toward the field margins. Sweep-netting, particularly along field edges, can be used to determine stinkbug abundance in soybean and other field crops.

In orchards, BMSB can be highly cryptic, and are often found in the tops of trees. Limb jarring over a beating sheet can be a good way to determine if they are lurking in the upper canopy of an orchard.

There are many BMSB monitoring traps available; all must be baited with a lure. Placement is critical so scouts should follow the manufacturer’s directions. Our observations suggest that lures work best when BMSB are abundant in the landscape and ready to aggregate; aggregation behavior begins in late August through the fall.

Visual observations to detect feeding damage is challenging because symptoms may not appear for up to three weeks after it occurred. To assess damage in orchards, collect 100 fruit at random from a block and count the number of fruit with suspected stinkbug damage. This number can be used to generate a percentage of damaged fruit in that block. Ensure that fruit are collected at random or there is risk of overestimating damage. Lastly, sampling in blocks adjacent to other favored crops or habitats should take precedence.

Over the next few seasons we expect BMSB populations to continue to build in croplands. In the meantime, read up on how best to manage this pest in Michigan orchards.

For information on managing BMSB in other crops, check out stopBMSB.org.

Wilson writes from the entomology department at Michigan State University.