The dreaded brown marmorated stinkbug is gradually making its way towards major tree fruit and grape growing regions in Oregon and Washington where $4 billion in crops are at risk.
This stinkbug species, which originated in Asia, is much larger than native stinkbugs and can be far more damaging. It has a host range of more than 300 crops.
It was first collected in Pennsylvania in the 1990s, but not officially identified until 2001. It began to be a problem in Mid-Atlantic tree fruit orchards in 2008, and caused an estimated $37 million in damage to apples in the region in 2010, as well as extensive damage to peaches.
The brown marmorated stinkbug’s first appearance on the West Coast was in Portland, Oregon, in 2004. It has not yet been found in commercial orchards in the region, Dr. Peter Shearer, director of Oregon State University’s Mid-Columbia Agricultural Research and Extension Center, told growers during the Washington State Horticultural Association’s annual meeting in December, but it is moving steadily towards them.
From Portland, it has been spreading south down the Willamette Valley towards Oregon’s Pinot Noir grape growing region.
At the same time, it has spread north across the Columbia River to Vancouver, Washington. It turned up at Arlington in eastern Oregon, presumably after hitching a ride on a dump truck to the landfill there. It’s moved east along the Columbia Gorge and was found literally on Shearer’s doorstep—outside his office—last year. It is now within 60 miles of Yakima, Washington’s main fruit growing region.
“So, it’s coming,” warned Shearer, who is hoping that biological controls will be developed before the pest becomes established as an orchard pest in the West. “This is going to be the thing that saves us from this beast. Ultimately, a successful biocontrol program is going to be the key to mitigating this problem. We’ll have the good bugs take care of the bad bugs, so we don’t have to use a lot of chemicals to take care of them.”
The U.S. Department of Agriculture has imported a couple of promising parasitic wasps from Asia in the hope that they might be able to control the brown marmorated stinkbug. One, Trissolcus halyomorphae, is in quarantine at Shearer’s lab. Next year, OSU scientists will begin collecting specimens of native beneficial stinkbugs to make sure that the parasite won’t have a negative impact on them, since they are important predators of orchard pests.
Shearer and other scientists at OSU and Washington State University are collaborating in a nationwide research project on the bug that has been funded by the federal Specialty Crop Research Initiative for three years. Fourteen institutions across the country are involved, with Tracy Leskey, with USDA in Kearneysville, West Virginia, as lead investigator. Aims are to understand the biology and phenology of the bug, develop monitoring and management tools, and develop effective chemical management programs.
Because the bugs are difficult to kill with insecticides, they’ve been a major disruption to both conventional and organic international pest management programs in the East, Leskey said. “We’ve been in crisis mode and want to understand how to keep our growers in business.”
Some classes of pesticides knock down the bugs, but they are able to recover. Leskey’s seen orchards where, after treatment, there was a carpet of bugs on the ground, but within 48 hours they start recovering and climbing back up into the trees.
Working with scientists at Pennsylvania State University and Virginia Tech, Leskey has been doing lab tests to assess the effectiveness of more than 40 pesticides on brown marmorated stinkbugs. Bugs were exposed to dry pesticide residues for 4.5 hours, and their mortality was tracked for seven days to make sure those that looked moribund actually died. The scientists saw the knockdown and recovery effect from pyrethroids and nicotinoids. The broad-spectrum, highly regulated materials looked the most promising, Leskey reported.
“There’s no chemical class that was perfect, but within each chemical class, we did find promising materials.”
However, results in the lab haven’t always translated to the field because few materials have more than three days of residual activity against immigrating adult bugs. Eastern growers have taken a conservative approach and have been spraying alternate row middles every seven to ten days, or three to four days during peak periods of activity. On larger farms, where it might take seven days to cover the acreage, growers are spraying every single day, she said. On diversified farms, every crop is at risk.
Another problem is that growers are reaching the maximum seasonal label rate on some materials, she said. The best strategy would be to target the bug with those products only at times when the crop is most at risk. For example, peaches become vulnerable as soon as after fruit set. If they are controlled at that time, the fruit should not be vulnerable again until midseason and then again during the late season when there are fewer other hosts available for the bugs.
Leskey and her colleagues are looking at combining visual and olfactory stimuli as monitoring tools. They tested a pyramid trap baited with methyl decanoate, a substance reported to be attractive to stinkbugs, but it failed to catch stinkbugs during the early and midseason in a peach orchard, even though there were 20 to 50 bugs in each tree. Agricultural Research Service scientists are working to develop an aggregation pheromone as a lure that might be more attractive to the bugs.
Scientists are also exploring visual cues, and identifying optimal wavelengths and intensities of light to attract the insects to traps. In tests the last couple of years, traps with lights captured 200 to 400 times more stinkbugs than unlit traps. Leskey said the scientists will continue the work to make sure they can attract bugs earlier in the season as well as during the summer. If successful, this method could potentially be used as part of an attract-and-kill strategy.
The bug commonly overwinters in houses and buildings—one homeowner counted 26,000 bugs in an attic in 2011—but one of the questions researchers hope to answer is where it overwinters in nature. Leskey said the bug can overwinter in standing dead trees, but she will be working with the USDA’s Animal and Plant Health Inspection Service to use sniffer dogs to detect bugs in other overwintering sites.