Continued brown marmorated stink bug trap catches and some fruit damage in east Michigan

For the second week, trap catches of brown marmorated stink bugs have been on the rise, seen now in seven of the 10 trapping sites in east Michigan orchards with some fruit feeding damage as well.

Again this week we are seeing a strong trap catch of adult brown marmorated stink bugs in traps scattered over eastern Michigan orchards. Last week, we saw trap catches in half of the 10 trapping sites, and this week that number increased to seven of the 10 trapping sites. These trap catches started Sunday, Sept. 25, and Tuesday, Sept. 27.

Last week’s trap catches occurred in Genesee, Lenawee, Oakland and Washtenaw counties, and in the last few days Macomb County saw its first trap catch. Earlier this summer, MSU set up a network of more than 80 trapping sites in orchards and vegetable farms across the state, with 10 sites here in east Michigan.

I had several reports in the last few days of fruit growers finding brown marmorated stink bug adults crawling on empty apple bins, window screens and on farm buildings, and even on some people, mostly on sunny afternoons. We are finding that scouting for brown marmorated stink bugs in orchards and adjacent fields and woodlots is difficult to do, as this pest is rather illusive.

I found some limited late-season feeding damage on apples at all but one of the nine fruit farms I visited Monday and Tuesday of this week (Oct. 3-4). The list of apple varieties where I saw damage has also greatly expended in the last two days, now including Gala, Golden Delicious, Empire, Jonagold, Cortland, Red Delicious, Northern Spy, Crispin (Mutsu) and Cameo. I expect that as we move through apple harvest, we may see damage on other varieties.

This feeding damage most likely occurred in the last two to three weeks. It is hard to say at this time why brown marmorated stink bug adults are attracted to certain apple varieties at certain times, and yet will leave neighboring varieties undamaged. Brown marmorated stink bugs also feed on a wide variety of other plants that are common throughout Michigan.

As you are harvesting or grading fruit, be on the lookout for damage that at first glance looks like bitter pit or hail injury, but take a closer look. Damage is most often first mistaken for bitter pit symptoms, which is related to a calcium disorder. It is very difficult to tell the difference between bitter pit, hail and brown marmorated stink bug injury. Late-season feeding usually causes depressions on the fruit surface and the appearance of necrotic tissue or corking just below the fruit surface. Late-season brown marmorated stink bug feeding damage may look different than early-season damage. Bitter pit is usually concentrated on the calyx end of the apple and brown marmorated stink bug injury can be anywhere on the fruit. For pictures of brown marmorated stink bug injury on apples, see “Brown marmorated stink bug trap catches increased heavily in east Michigan.”

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