The brown marmorated stinkbug is a challenge to control for any fruit grower, and organic growers have the fewest strategies of all.
That’s why Win Cowgill and colleagues at Rutgers Cooperative Extension in New Jersey decided to test the effects of the kaolin clay product Surround on the stinkbug.
Surround is used against several pests, including pear psylla. The insects are repelled by the clay on the trees and deterred from laying eggs.
Cowgill conducted the trial at a mature Suncrisp apple block at Rutgers in 2010 and 2011. Surround was applied three times in the early part of the season as a protectant and then combined with various insecticides that were applied four times in August and September when the orchard was under threat from the pest.
These Surround-pesticide treatments were compared with Surround applied each time without an insecticide, and an untreated control. Fruit damage was assessed in August and October, and then at harvest.
Cowgill said his experiment was designed to evaluate treatments late in the season when the bugs begin to congregate for the fall and typically cause the most injury to fruit, but it was challenging to design the experiment and collect data.
“The challenge with this insect is it’s very hard to scout for, so it’s hard to tell when it’s in the orchard in high enough numbers. It’s kind of like if you see some, it’s time to start spraying, and that’s not a good way to control any pest.”
Complicating matters is the fact that the bugs are very strong fliers and tend to move in and out of orchards, Cowgill said. “They come in and take a few bites, and head out.”
One of the current recommended monitoring methods for the pest is to stand in the orchard and watch for three minutes and count how many bugs you see. However, that only works if the bugs don’t see you first.
“They’re a very ingenious insect,” Cowgill said. “They’ll crawl on the back side of the leaf and hide from you.”
Researchers around the country have been working on various types of traps and lures to monitor the pest, but there is still no effective way to predict when treatments should be applied, Cowgill said.
“Do you spray all season long from when you first see stinkbugs or wait until the numbers come up and then start?” he asked.
Although, numerically, the untreated control in the trial had more external damage from the pest, the results were not statistically significant (see “Effects of Surround on stinkbug”).
However, Cowgill believes Surround does act as a repellent, and he thinks the clay also might help prolong the residual life of the insecticides, though it will not be a stand-alone strategy.
“My sense would be that it’s going to do some good for that insect,” he said. “I think what will happen is when we learn more about the insect and can predict population levels and thresholds better, you could predict when to use the material and use it as a protectant once you know you have a population there.”
He would like to see it studied further.
Scientists in the eastern part of the country are puzzling over why the bug is more of a problem some years than others. Three years ago, populations grew so huge that some peach growers lost 90 percent of their crop to damage.
The last two seasons, populations have been lower, though still bad enough to cause commercial fruit damage, Cowgill said. In apples, feeding by the bugs causes dimpling and brown, corky spots under the skin.
Damage is not always noticeable at harvest but becomes worse during storage.
“Unless you know what you’re looking for, it’s easy to miss until it’s in the bin,” he warned.