Residents of California, especially those living in cities like Los Angeles, Sacramento and Yuba City, are no strangers to the brown marmorated stink bug (BMSB) as these insects seek and aggregate in homes and businesses for overwintering in the late fall season.  

First discovered in California in 2006, the stink bug has largely been limited to urban areas at first, primarily to feed on ornamentals and backyard variety fruit trees. They also feed on seed pods of a variety of ornamental and shrub species, and especially its favorite, the tree-of-heaven (Ailanthus altissima).

But according to USDA’s Animal & Plant Health Inspection Service (APHIS), the BMSB also can be a major threat to commercial and garden vegetable crops like tomato, sweet and field corn varieties, cotton, soybeans, lima beans, snap peas, peppers and fruit trees like apple, peach, pear, and nectarine. Raspberries, blueberries, cherries, pecans, hazelnut, grape and most recently almonds are also at risk.

A voracious feeder, overall 170 host plants can be targeted and the damages it can cause can be moderate to devastating depending on population levels.

University of California Cooperative Extension (UCCE) reported last week that in May, a Turlock almond grower reported nearly all the nuts in one row of his almond orchard had fallen to the ground. UCCE Integrated Pest Management advisor Jhalendra Rijal responded to the call to discover an infestation of BMSB were responsible.

He said this is not the first time he has seen BMSB damage in almonds. The stink bug was found in two other Valley counties in 2017 and 2018 respectively. While the Turlock orchard received the greatest damage in 2019 so far, Rijal said three other almond orchards have also experienced some level of damage from the pest.

“We have also successfully trapped BMSB in peach orchards as far back as 2016,” Rijal said, an indication the pest may be expanding its presence. 

Discovery of the pest in Turlock, located between Merced and Modesto, represents a concern for farmers of the area as it could mean increased movement of the pest from cities and into more commercial orchards.

According to UC Cooperative Extension’s Jeanette Warnert, a 2013 infestation of the pest in midtown Sacramento has been the most serious outbreak since BMSB moved into California, though in 2016 there were a few reports of the stink bug filtering into Stanislaus County. That’s when Rijal first began actively researching and tracking the pest and the risks it poses to commercial agriculture.

Orchard demonstration

Warnert reported last week that Rijal staged a gathering of growers and pest control advisers at the Turlock orchard on Aug. 13 to provide a demonstration of the types of damages the stink bugs can cause and how to recognize and detect the pests.

"I recommend growers and pest control advisors put BMSB traps in orchard edges if they suspect BMSB damage or if the orchard is located near potential overwintering structures or host crops," Rijal said. "BMSB are good flyers and active throughout the season, damaging nuts from April through the fall. But the most substantial damage happens in the spring through early summer."

Rijal reports the pest has now been found in commercial peach and almond orchards in Stanislaus and Merced counties.

According to stopbmsb.org, BMSB is difficult to detect in some vegetation. While the adult stink bug is typically shaped and marbled brown in color, eggs are barrel shaped, white to pale green, and laid in clusters on leaves. Nymphs shed their outer skin (molt) as they progress through five stages or nymphal instars before becoming adults.

In the fall BMSB adults aggregate in large numbers on the sides of buildings or on trees. They then move to protected places and overwinter as adults in a state of facultative diapause, or resting stage. In urban areas they can become problematic in large numbers, often found nesting between interior and exterior walls of homes and outbuildings and even attics.

According to USDA-APHIS, Halyomorpha halys is a native of Asia and has been expanding its range in the U.S. since its U.S. discovery in Allentown, Pennsylvania, around 1996. At last count it can be found in 40 U.S. states.

Management and control of the pest can be difficult. Entomologists warn the stink bug poses real danger to commercial crops and ornamental plants alike, and methods of control and eradication are still being explored and tested across the nation.

A major risk of movement exists because the pest often attaches itself to vehicles, including trucks, or lays eggs in shipments of nursery stock that can hatch after traveling between locations. Homeowners are warned to monitor their gardens and yards for presence of the pest and to report outbreaks to extension officials immediately.

Rijal says he has used traps to confirm the presence of BMSB in orchards and has been monitoring noticeable damage in tree crops.

“Although BMSB can feed on pistachios, my work has been focused on almonds and peaches. We don't know whether BMSB attacks walnuts or not at this point,” he told Western Farm Press last week.

Rijal says Mark Hoddle, UC Cooperative Extension specialist in the Department of Entomology at University of California (UC), Riverside, along with a group of UC researchers, have established that BMSB can feed on pistachio by testing BMSB feeding habits in the lab.

“But to my knowledge no reports of BMSB damage has been reported in a commercial pistachio orchard to date,” he added.

Successful trapping of BMSB

“We used sticky panel traps baited with the standard BMSB commercial pheromone lures to capture BMSB, both adults and immatures. Traps should be placed on the ground at orchard edges using a 4-foot tall wooden stake and sticky panel and lure on the top of the stake.”

He says so far BMSB has not been detected in California apple or pear orchards, although those crops are known hosts for the pests and are being affected in other states such as Virginia, West Virginia, New York and others.

Though thresholds have not been established for the stink bug yet, Rijal says farmers should use traps and monitor for visual signs of damage in their crop.

“At this point, watching out for any indication of BMSB presence in orchards is important. We are working to develop some provisional pest control recommendations currently to address this insect in almonds.”

 At the time of this writing, there is no recommended insecticide that is successful on BMSB.

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