Eastern growers and researchers say they know more now than they did a year ago about the invasive brown marmorated stink bug.
But they also admit that the pest’s sheer numbers and wide host range make it extremely tough to control. Ultimately, they say, the battle will require creative approaches that rely on more than just insecticides.
“We still hope that someone will come up with some type of behavior modification product—an attractant, repellant, aggregation pheromone or sex pheromone—something that will help us affect the behavior of the stunk bugs away from the orchard,” says Greg Krawczyk, Extension tree fruit entomologist at Penn State University’s Fruit Research and Extension Center in Biglerville. “Then those insecticides will be much more effective.”
A wide host range
The other challenge is the stink bug’s wide host range, estimated at more than 300 different plants.
During the spring, Tom Kuhar, an associate entomology professor at Virginia Tech University in Blacksburg, says he’s found BMSB en masse under the bark of several invasive Asian trees, such as mimosa, paulownia and tree of heaven or Chinese sumac, that grow along roadways and in wooded areas near farms.
Among commercial crops, both adult BMSB and immature, or nymphs, feed readily on pome fruit, stone fruit, fruiting vegetables, green beans, lima beans, soybeans and corn—including sweet corn.
In addition, BMSB invade homes in huge numbers in the fall as they aggregate to overwinter.
A nemesis of fruit growers
Like many other true bugs, BMSB insert straw-like stylets into the crop to suck out plant juices. As BMSB feed, they inject saliva that damages the tissue around the feeding hole.
In peaches, BMSB actively target the fruit between shuck split/shuck fall and pit hardening— sometime around late May and early June, says Tracey Leskey, a research entomologist with the Agricultural Research Service’s Appalachian Fruit Research Station in Kearneysville, W. Va.
Hard or corky pockets develop around the feeding site, making the fruit unmarketable. “This is the injury that really devastated a lot of the peach growers in 2010,” she says. The late spring timing also coincides with the emergence of the overwintered generation of BMSB, which favors trees—whether wooded areas or commercial orchards, says Kumar, citing two seasons’ worth of observations.
Many peach growers appeared to be more aware of the threat this year and waged a campaign that significantly reduced the early fruit damage, Leskey says.
Another key period is later in the season as the peaches reach maturity and have higher Brix, which is believed to attract the pests, she says.
In apples, Leskey says it appears the early feeding does not cause the hard pockets seen in peaches.
As with peaches, though, apples become more attractive and more susceptible to injury as they reach maturity. This occurs from mid-June on, depending on the cultivar.
She bases her comments on the results of intensive sampling of 10 apple orchards in West Virginia and Maryland this season.
Phil Glaize, a Winchester, Va., apple grower, says he began to see BMSB damage in mid-August, although he couldn’t find any stink bugs.
Leskey says this is common, since BMSB also can feed at night and tend to prefer the upper tree canopy.
The crucial time for apples is between mid-August and harvest, Glaize says. “We’re actively trying to control them because we think they are there,” he said in mid-August. “We’ll start throwing the book at them in late August through September.”
Glaize says the Section 18 emergency use exemption for dinotefuran will be a big help, since the insecticide only has a one-day preharvest interval. Unfortunately, he says, it’s very expensive.
One of his concerns is the harsh chemicals needed to fight BMSB have disrupted his integrated pest management program.
“Mating disruption reduced our use of pesticides, and then the stink bug came roaring through,” Glaize says.
Stink bug diet preferences
Vegetables are not immune to BMSB feeding, either.
Galen Dively, an emeritus entomology professor at the University of Maryland in College Park, has separate pepper and tomato field trials examining the efficacy of 10 to 12 organic and conventional insecticides. He also has two conventional insecticide trials on peppers that involve pyrethroids or combinations of another insecticide with a pyrethroid.
In addition, Dively has a host preference trial at each of the university’s three research farms. Each trial involves plots of trellised tomatoes, peppers, squash, okra, sweet corn, eggplant and green beans. The plots are not sprayed with insecticide.
The goal is to see what crops BMSB prefer and the types of damage to each.
Based on early observations, Dively says BMSB favor the fruiting parts of eggplant but not necessarily the fruit.
“Right from the beginning, I think they’re causing more damage to the fruiting parts so you don’t get any fruit set,” he says.
Sweet corn seems to be another preferred host, Dively says, based on his observations.
Early in the season, BMSB feed on the green tassels so you don’t get good kernel fill in the ear.
“Seventy-five percent of the ears weren’t filled out,” he says. “On top of that, the more obvious injury is what they do to the kernels.” Later in the season as the ears start to fill, BMSB are able to pierce corn husks with their stylets to feed on developing kernels.
Given a choice, BMSB appear to favor peppers over tomatoes, and squash appear to be low on the list of preferred crops, Dively says.
In okra, BMSB feeding causes curled pods.
Based on what he’s seen this year, Dively says he’d like to expand the host trials next year to compare untreated plots against treated plots.
“We’re missing the yield impacts of this insect,” he says. “We have the fruit quality impacts. We now need to try to figure out how many bugs it takes to cause a certain amount of yield loss.”