How Nut Growers Can Get the Best of Brown Marmorated Stink Bug

In the Central Valley of California, we first located a large population of brown marmorated stink bug (BMSB) in Sacramento in 2013. Since then, it has been spread to 16 counties, and largely remains as a backyard nuisance and in several cities and towns. In 2017, we reported the infestation of brown marmorated stink bug in a commercial almond orchard near Modesto in Stanislaus County. Since then, this pest has been detected alive and in traps in several almond and peach orchards in the Northern San Joaquin Valley, and has begun to cause economic damage to a few almond orchards in the area. Although the BMSB population in the commercial orchard is limited to a few counties to this date, when present, they are causing economic damage to crops — in some cases, very substantial damage.

Advertisement

Brown marmorated stink bug is a new invasive stink bug species to the U.S. and has spread to more than 44 states since its introduction in Pennsylvania in the early 2000s, causing economic damage to multiple crops. The adult stink bug is about ¾ inch long, has a shield shape, is marble brown in color and typically has two white bands in the antennae. Similar to other stink and plant bugs, BMSB also has straw-like piercing and sucking mouthparts for feeding.

BMSB attacks multiple host plants (more than 170 host plant species reported, stopbmsb.org) including crops and other ornamental and landscape trees. The major host crops include apples, peaches, nectarines, pears, cherries, grapes, peppers, tomatoes, sweet corn, beans, soybean, and more. BMSB adults overwinter in man-made structures such as houses, barns, shops, and even in dry and dead trees during the fall and early winter. Therefore, BMSB is also considered a significant nuisance pest in residential areas when populations get established.

HOW TO DETECT

The brown marmorated stink bug causes damage when it punctures the nut and inserts its straw-like mouthparts into the fruit, releasing a small amount of digestive enzyme to dissolve the fruit’s tissue, and sucks out the juice. In peach, feeding damage creates a depression on the surface, and corky tissue internally, that renders unfit for consumption. The almond hull shows feeding signs externally (multiple gumming, light brown speckles, and yellowing) as well as internally (brown and cork tissue and internal gumming).

Top Articles
Have a Plan For Climate Change? Why Fruit Growers Need To Act Now

If feeding occurs early in the season during the spring (March to May), it can cause nut abortion and nut drop. Mid- to late-season (May to July) feeding on the nuts can result in kernel damage that includes gumming, shriveled kernels with dark sunken spots, and dimpled kernels. Some of these feeding signs match with that from the leaffooted bug and native stink bug feeding damage in almonds. The presence of adults and the feeding damage have been noticeably higher in the border rows, mostly in a side of the orchard next to the open field or alternate hosts such as tree of heaven, Ailanthus altissima, which are abundant in many residential areas.

BMSB adults can be active and begin to move into the crop from nearby overwintering shelters as early as March, and therefore, the detection of that first moving population at the orchard edge in traps is important. To monitor for BMSB in the orchard with traps, growers and PCAs should use a commercially available BMSB lure in a clear sticky panel (9 inches x 12 inches) that is affixed to the top of a 4-foot-long wooden stake installed in the ground.

A minimum of three of these traps should be placed at least 50 feet apart in an orchard along orchard borders to intercept the BMSB activity when these adults are moving into the orchard from nearby overwintering habitats such as homes, barns, or early-season preferred hosts (e.g., tree
of heaven).

In addition to putting out traps, it is important to scout BMSB activities regularly in the orchard. Visual observations of the insect (egg mass, immatures, and adults) and damaged fruits (deformed fruits and exuded fruits) and beat tray sampling (shaking branches/twigs to dislodge insects from the tree) are early BMSB detection methods. Visual observation of the border trees for the presence of insects and gumming fruits is highly recommended.

HOW TO MANAGE

Scout for BMSB using traps and visual sampling methods, as BMSB populations are expanding to more commercial orchards every year. It is important to understand the basic biology of BMSB and the presence of any potential overwintering structures of alternate host plants near the orchards. Since BMSB infestation in California’s commercial orchards is relatively new, we are still learning about the specific control methods that can be recommended for growers. At this point, the use of insecticides targeting the plant bug and other native stink bug species in almonds and peaches may be the best option to use.

In general, pyrethroids and some neonicotinoid insecticides are considered to be effective. However, these insecticides are a poor fit into an IPM program because of their negative impact on predators and other beneficial arthropods. For organic production, a few neem-based products, Spinosad, pyrethrum, and pyrethrin insecticides are available, but not surprisingly, the efficacies of these products are weaker compared to conventional insecticides in general and may require more frequent treatment.

Follow the pesticide label, and some specific label restrictions for the target crop, pre-harvest interval (PHI), re-entry interval (REI), etc. For example, the use of pyrethroids in the spring can destroy predators of spider mites, resulting in a flare-up of the mite population in almond and other tree fruit orchards.

BMSB is an invasive pest and does not have any active biological control agents specific to it. However, in the past few years, a BMSB-specific parasitic wasp of Asian origin, samurai wasp (Trissolcus japonicus) has been found in several states. Certainly, it takes time to test these types of biocontrol agents, especially for control on a mass scale. However, we can hope that these kinds of biocontrol agents may be available in the future to minimize the impact of the BMSB population.

0