Support scientist Starker Wright, left, and entomologist Tracy Leskey inspect traps baited with experimental pheromone lures. The lures are being tested for brown marmorated stinkbug attraction.
Photo by Stephen Ausmus.
Although growers probably can't believe there's any good news about the brown marmorated stinkbug (BMSB), there are some new developments worth following this season.
Now in the fourth year of battling the invasive Asian insect, researchers and growers have more information on the most effective management tools. Dr. Greg Krawczyk, Penn State Extension entomologist, said that the early years were hit-and-miss.
"Some of the applications we did the last few years were not really necessary," noted Krawczyk. "Everything we did against stinkbugs made sense, but we didn't know what to expect. I said, and a lot of people said, that the only way to control stinkbugs is to use insecticides, because we don't know when they will strike."
Dr. Tracy Leskey, a research entomologist with the U.S. Department of Agriculture's Agricultural Research Service (USDA-ARS), provided background on how the pest was managed the first few years it was found in orchards.
"In 2011, we had one attractant available; that was referred to as methyl decatrienoate. It wasn't the pheromone of the BMSB, but it's the pheromone of another Asian species, and was only attractive to adults in the late season, and in this case postharvest. During the period of invasion, we were not getting any adults in the traps. However, during the same year, we made some significant breakthroughs with our first tentative identification of the BMSB aggregation pheromone, which we refer to as #10," Leskey explained.
This discovery came late in the season and was based on work at the Appalachian Fruit Research Station in Kearneysville, West Virginia, along with work at the USDA-ARS lab in Beltsville, Maryland. "In 2012, that led to a broad validation in terms of a trial comparing the attractiveness of #10 to the late-season methyl decatrienoate," Leskey said. "We asked three key questions: Is BMSB attracted to this #10 pheromone early in the season? That was a piece we were missing. Also, is it attractive to the BMSB all season long? And how attractive is this stimulus relative to the late-season attractant?"
To answer these questions, more trials were conducted. Leskey noted that a number of collaborators were involved, and the trial was standardized as much as possible. Black rocket traps were baited with a small dose of the pheromone alone and compared with traps containing methyl decatrienoate and unbaited control traps. All traps were located in agricultural production areas near wild host habitats.
"In orchards, they were typically in a perimeter row next to a woodlot," Leskey noted. "Traps were deployed from mid-April through harvest. We found good activity with the #10 pheromone early in the season. In the early season, from mid-April to mid-June, there are almost no nymphs in the field, so there were no captures. In midseason, there are low numbers of adults in the fields, but since there is a lot of reproduction, there are a lot of nymphs in traps. Late season, there was response to both #10 and methyl decatrienoate. This told us that we were well on our way to being able to monitor for this pest all season long."
Leskey compared the results with the known behavior of native stinkbugs regarding patterns of activity in the field. "There are lower to moderate populations in early to midseason, and they peak in late fall," she said. "We see that in our orchards where there's a lot of activity late in the season."
The next step in the process is applying the information collected during trials, so Leskey is currently developing tools to help growers make treatment decisions.
Based on Leskey's research as well as his own, Krawczyk urged growers to use traps in 2014.
"This year, we have commercially available traps and lures that will help monitor BMSB. The traps we are using are not to control the stinkbug; they are for monitoring," noted Krawczyk.
The lures in traps are aggregation pheromone lures, which are different from sex pheromone lures. "Aggregation pheromones attract males and females, and also attract juvenile stages," he explained. "When the insects find a place they can eat, they release the aggregation pheromone so other stinkbugs will come. Juvenile stages will come too. If you put a trap on your tree or under the tree, don't be surprised if that tree has 90 percent or higher injured fruit. It's because they are coming to the trap; they're coming to the area where the aggregation pheromone is."
Adult stinkbugs are migratory, so one or two adults in a trap does not mean there's an established population. However, once nymphs appear in the traps, they are no longer migratory - they are resident pests and need to be controlled.
"Catching nymphs in the traps is the best threshold we have for the spray," Krawczyk said. "Adults might be on their way out of the orchard, or just flying by."
Rather than simply checking traps and counting stinkbugs, growers should spend a few minutes looking in areas around the trap. If stinkbugs are present in the orchard, it's likely that they'll be close to the traps. Growers should be able to use the traps as a basis for making spray decisions. If traps at the edges of orchards are not catching anything in late July, August and September, there are likely no stinkbugs, so there's no need to spray.
Krawczyk noted that growers can purchase stinkbug traps and lures at big box stores. He advised purchasing lures that say nine weeks rather than seven weeks on the packaging. "Again, the trap will not protect crops," he emphasized. "Traps will only tell you that you need to do something to protect the crop."
Krawczyk said that at this time, bifenthrin is the most effective product for killing the BMSB, and it has great residual activity on nymphs.
"In the trials we did in 2011, where we sprayed bifenthrin on the trees and collected foliage from those trees, we found that the residue on foliage was active two weeks later to kill nymphs," he said. "However, with the traps and lures, I hope that growers can try to avoid a spray schedule for stinkbugs. Place them at the edge of the orchard where you expect they will be coming from, and maybe it will help save some sprays."
The author is a frequent contributor and freelance writer who farms and raises Great Pyrenees in south-central Pennsylvania. Comment or question? Visit http://www.farmingforumsite.com and join in the discussions.