UNIVERSITY PARK, Pa. — What was once considered a nuisance pest has now become a major threat to Pennsylvania grain, fruit orchards and vegetable fields, and experts are scrambling to discover ways to get rid of them.
Brown marmorated stink bugs find their way into homes in the fall, looking for a place to over-winter as the weather cools. They can be annoying in large numbers, especially because they emit a citrusy odor, but are not considered harmful to people.
However, in the past year they have become a major pest to growers in southern Pennsylvania and beyond.
According to Greg Krawczyk, an entomologist at the Penn State Fruit Research and Extension Center in Biglerville, some fruit orchards have lost up to 60 percent of their crops to the bugs, particularly in the southern counties, northern Maryland and West Virginia.
“Stink bugs are native to Asia and were first detected in Pennsylvania in the late 1990s. They’ve spread rapidly because they have no natural biological controls here, and they are strong fliers and hitchhikers.”
Typically, biological controls include predators and parasites that hold the pest population in check. Reliance on biological controls part of an integrated pest management program, or IPM, have been an important part of agriculture.
For years, fruit growers have relied on IPM to manage pests in their orchards as an alternative to excessive pesticide applications. IPM aims to manage pests — such as insects, diseases, weeds and animals — by combining physical, biological and chemical tactics that are safe, profitable and environmentally compatible.
In addition, other crops, including peppers, tomatoes, and soybeans, have been heavily affected in certain areas. According to John Tooker, assistant professor of entomology at Penn State, damage appears widespread in the infested fields he’s inspected.
“Stink bugs are consistently the biggest insect challenge facing soybean growers in the southern United States and it now seems that we are going to have to battle them as well.”
Stink bugs can feed on many different fruit or vegetable crops throughout the growing season, which is another one of the reasons stink bugs are spreading rapidly, said Krawczyk.
“The bugs suck out the juice, and by destroying cell walls it causes the fruit to dry out from the inside and become brownish and distorted. This renders the fruit unsalable to the fresh fruit market, so the grower makes little to no profit on the damaged fruit.”
Previously, it was thought that in Pennsylvania stink bugs produced only one generation a year. But this year there seems to be multiple generations, explained Krawczyk.
“That means they can infest a crop at almost any time during the growing season. As late as September, we were still finding nymphs and adults in the field at the same time.”
More information needed
Because stink bugs did not cause much damage to crops before this year, there was a very little research conducted on this species.
“We don’t have a good monitoring or trapping system. Because they are so new, we haven’t identified a sex pheromone to trap them,” Krawczyk explained. “At the USDA, research is ongoing to identify a pheromone specific to this species of stink bug. However, it will take the efforts of many agencies, researchers and growers working together to hopefully come up with a solution.”
In the meantime, Krawczyk is advising growers to use broad-spectrum pesticides judiciously, as it seems they are the only effective means of control at the moment. However, he warns that these types of pesticides only work on the adult bugs and nymphs by direct contact and only at the time of application.
“There is not effective residual control from pesticides, so spraying this week won’t prevent problems a week later,” he said.
Broad-spectrum pesticides need to be used carefully, because they also kill non-targeted organisms such as beneficial insects, hindering many growers’ IPM programs.
In addition, Tooker advises growers to strongly consider the anticipated economic value of any treatment versus the cost of the application.
As a short term goal researchers will be evaluating different types of pesticides over the next several months trying to assess compounds from various chemical groups attempting to determine if less toxic, more selective products are available to control brown marmorated stink bug.
For more information, see the Northeastern IPM Center Regional Pest Alert on BMSB at www.hgic.umd.edu/_media/documents/publications/Stink_Bug_Pest_Alert.pdf or Penn State’s Department of Entomology’s fact sheet at http://ento.psu.edu/extension/factsheets/pdf/BrownMarmoratedStinkBug.pdf.
The Pennsylvania IPM program is a collaboration between the Pennsylvania State University and the Pennsylvania Department of Agriculture aimed at promoting integrated pest management in both agricultural and urban settings.
For more information, contact the program at 814-865-2839, or visit www.paipm.org.