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Stinkbugs are likely to move into cherry orchards by mid- to late July.

Stinkbugs are likely to move into cherry orchards by mid- to late July.

Photo courtesy of washington state University

Stinkbugs in the past haven’t been of much concern for Pacific Northwest cherry growers. But with later varieties now being grown and extended growing seasons, stinkbugs could be a pest to watch for, including the feared brown ­marmorated stinkbug.

A few years ago, a Chelan, Washington, cherry grower had problems with the Chlorochroa species of stinkbug that resulted in fruit pitting, according to Dr. Jay ­Brunner, Washington State University entomologist. Damage to cherries occurred in late varieties that were harvested in August at high elevations.

“While this is an unusual situation, it points to the potential for the pest to attack cherries that are harvested later in the season,” Brunner said. At the orchard in Chelan, when foam pads were pulled up from the bins with picked fruit, 50 to 60 stinkbugs readily came out of the fruit, and damage was severe. The grower treated the borders of the orchard with pyrethroids and hasn’t had any problems since.

Northwest apple and pear growers are familiar with four species of stinkbugs—consperse, Chlorochroa spp. (no common name), green soldier bug, and the red-shouldered stinkbug. Consperse is the most common in tree fruit, with the other three more infrequent orchard pests. “The native stinkbugs we have usually come into orchards looking for water and nutrients,” Brunner said to growers attending the Northwest Cherry Institute ­meeting in January in Yakima, Washington.

In apples, stinkbug damage tends to be regional, not widespread in the state. The pest pierces the fruit and feeds by sucking out juices. Superficially, apple damage from stinkbug looks a lot like bitter pit with external indentations, he said. In cherries, the damage looked like pitting.

“The natives move in from the outside usually in mid- to late July and, by managing the borders, we can usually reduce their impact. However, they spend most of their time outside the orchard, which makes them difficult to control,” he said, adding that native stinkbugs overwinter on perennial vegetation like mullein, bitterbrush, and brambles.

With late-season cherries being grown in the orchard longer, Brunner sees potential for stinkbugs to be more of a problem in cherries than in the past. “In Chelan, it’s likely that stinkbugs moved into the orchard in early August as they often do, and cherries just happened to be there.”

Control

“The most effective pesticides on the native stinkbugs have been the broad spectrum chemicals—the ones that we want to avoid,” Brunner said.

In Washington, evaluations of chemicals to control native stinkbugs have relied on laboratory bioassays to screen different chemicals and field trials to validate lab results. “Most insecticides are not effective, even when tested at four times their dilute field rate,” he said. Organophosphate and organophosphate replacement insecticides were not effective.

The few insecticides that were effective include Carzol (formetanate hydrochloride), Lannate (methomyl), Thiodan (endosulfan), Danitol (fenpropathrin), and Warrior (lambda-cyhalothrin). Danitol and Warrior have a short residual effect, and all five insecticides have drawbacks, such as posing a toxicity risk to humans, being restricted to early season use, or causing problems with secondary pests.

Treat borders

A pheromone for consperse stinkbug has been optimized, and WSU researchers see potential in the use of pyramid traps with pheromone to help growers monitor adult movement. Growers can place the traps around the orchard borders in midsummer to get an idea of when consperse stinkbugs are moving. Brunner said WSU has demonstrated that if a good job of trapping is done, trap numbers per week of 20 stinkbugs or higher indicate the orchard is in a risky situation, and controls are warranted. Below 20 indicates risk is low. Because damage occurs primarily on border rows, treating borders on a regular schedule will help prevent damage to the rest of the orchard.

Another potential control technique might be to exploit the stinkbug’s aggregation behavior with attract-and-kill chemicals. In a trial that baited mullein plants with pheromone every 20 feet and was then sprayed weekly in the evening with a hand gun during the spring, harvest damage was reduced by 50 percent.

But the stinkbug picture is likely to change, he said, and not for the better. “The beast of the East—the brown marmorated stinkbug—is moving West,” Brunner said. The new beast feeds on a wide range of host plants and can complete its life cycle on tree fruit crops, meaning that adults and nymphs might cause injury in May and June if not controlled. In the Mid-Atlantic, the pest has two generations, but Brunner believes it will have only one in Washington.

“We think that the life cycle for the brown marmorated stinkbug will be similar to our native stinkbugs, and that by mid to late July, adults will begin moving into orchards.”

Brunner notes that one of the concerns is the movement across different cropping systems in the Columbia Basin, where tree fruit, row, and field crops are grown close together.

Concentrated research is going on both sides of the country to develop effective strategies and practices to manage the new pest, he said. Researchers are looking for an aggregation pheromone specific to brown marmorated stinkbug that might be used in traps to monitor for the insect. Other avenues being explored include bait-and-kill techniques, use of light to attract insects to the traps, and finding natural enemies of the brown marmorated stinkbug.