Brown Marmorated Stink Bugs Threaten Minnesota Apple Orchards

By Scout Nelson

Brown marmorated stink bugs (BMSB) are invasive insects that pose a threat to fruit crops, including apples. These pests feed directly on fruits and can cause visible damage, making apples unsuitable for sale. They also enter homes and buildings during colder months as they search for shelter.

In Minnesota, recent reports of BMSB activity in orchards raise concerns about possible crop damage. Growers are encouraged to watch these insects, check their orchards regularly, and report any signs of pest activity.

Madeline Wimmer, UMN Extension Fruit Production Educator, highlighted the importance of identifying and managing this pest in Minnesota orchards. Angie Ambourn, an entomologist with the Minnesota Department of Agriculture (MDA), has also received reports of BMSB activity from orchards in Washington and Scott counties. These reports highlight the need for better pest monitoring and information from growers to understand the spread and impact of this insect.

Brown Marmorated Stink Bugs in Minnesota

Brown marmorated stink bugs are considered serious agricultural pests in several parts of the United States, especially along the East Coast, in Michigan, and in Oregon. However, they have been detected in 48 states, including Minnesota. Although their impact is considered less severe in Minnesota, they still pose a risk to different agricultural crops.

Ramsey County was the first Minnesota county to report this pest in 2010. By 2019, BMSB had also been detected in Washington, Dakota, Chisago, Scott, Goodhue, Nicollet, and Carver counties. Through its trapping program, the MDA identified the insects in 15 orchards across these counties.

Reports of BMSB in Minnesota orchards have continued since 2019. However, the MDA has used fewer traps in recent years because of limited funding. Continued reports from growers can help experts understand where the pest is present and how much damage it causes.

How to Identify Brown Marmorated Stink Bugs?

Several stink bug species live in Minnesota, so growers need to identify BMSB correctly before taking action. Other species found in the state include brown, green, one-spotted, dusky, rough, and spined soldier stink bugs.

Brown marmorated stink bugs have a few features that help distinguish them from other species. These include light-colored bands on their antennae, metallic green spots underneath the head and thorax, and alternating light, and dark bands along the edges of their bodies beneath the wings.

The metallic green spots are easier to see with a hand lens. Growers can use identification guides from the MDA to compare BMSB with other stink bug species and avoid confusion.

Timing and Signs of Apple Damage

Brown marmorated stink bugs mate, and lay eggs earlier in the growing season. However, the main damage to apples comes from adult insects rather than their young. Unlike pests such as codling moths, and apple maggots, BMSB adults feed directly on fruit using piercing and sucking mouthparts. In some cases, damage to apple blossoms can also occur.

In Minnesota, apple orchards may face a greater risk of BMSB damage from late August through October. More research is needed to confirm this time. Some studies suggest that apples become more vulnerable when they are about four to eight weeks away from harvest. Early ripening apple varieties may face a lower risk.

The feeding activity of BMSB can make apples unsuitable for the fresh market. On the outside, damaged apples may show small depressions that look similar to bitter pit, especially in Honeycrisp varieties. However, the internal damage is different. Cutting open an affected apple may reveal uneven areas of corky tissue beneath the skin. These internal marks can be more serious and less uniform than the damage caused by bitter pit.

Monitoring and Managing BMSB

Regular monitoring helps growers understand pest activity and make better management decisions. Black pyramid traps and clear sticky card traps are useful tools for tracking BMSB populations. Special lures are also available and can improve the effectiveness of these traps.

The insects are more likely to be found in the upper parts of trees. Trees near wooded areas may also face a higher risk because these locations provide suitable surroundings for the pests. Placing traps between orchard rows and nearby wooded edges can help growers detect their presence.

The established economic threshold for BMSB is 10 adult insects per trap. However, growers need to consider trap location and whether a lure is used when checking trap counts. Traps placed near wooded areas or fitted with lures may collect more insects than other traps.

The Midwest Fruit Pest Management Guide provides information about controlling BMSB in apple orchards. It includes recommendations for pesticide use during the third and summer cover spray periods. Growers should base treatment decisions on trap results and established pest thresholds.

The guide also provides information about pesticide products that can help control BMSB. However, some treatments may harm beneficial insects and other organisms that help manage pests such as San Jose scale and mites. Growers should consider these effects before selecting a product.

UMN resources recommend applying pesticide products through alternate-row-middle spraying. After the first application, growers should wait seven days before applying another treatment. They should also rotate pesticides based on their classification to support effective pest management.

Management Options for Organic Growers

Organic growers can also use different methods to reduce BMSB activity. Research shows that a combination of azadirachtin, potassium salts, and pyrethrin can help control young stink bugs, known as nymphs. However, these products are less effective against adult insects and may sometimes cause phototoxicity, which can damage plant tissues.

Kaolin clay applications can also help protect crops when used at the right time and in the right way. Another possible method is using trap crops to attract stink bugs away from apple trees. Although more research is needed, trap crops may help delay the movement of these pests into orchards.

Growers Encouraged to Report Pest Activity

Reporting BMSB sightings and fruit damage is important for improving pest detection and management across Minnesota. Information from growers helps state experts understand how widely the insect has spread and how serious the problem is in different orchard areas.

Growers who find adult BMSB in traps or notice unusual damage on apples are encouraged to share their findings. They can contact Madeline Wimmer at wimm0035@umn.edu or Angie Ambourn at angie.ambourn@state.mn.us. They can also submit reports through the Minnesota Department of Agriculture's Report a Pest webpage.

Photo Credit: Angie  Ambourn