Your High Tunnels Might Be Susceptible to These Invaders
April 16, 2022 
While high tunnels increase in popularity among berry growers, they have long been the dream home of a few uninvited guests. Two of them, spotted wing drosophila (SWD) and two-spotted spider mites (TSSM), thrive in the warmer, drier controlled environment of a high tunnel.
Kathy Demchak, a Senior Extension Associate at Penn State University, discussed both pests while addressing common high tunnel problems at the annual conference of the North American Raspberry and Blueberry Association.
SPOTTED WING DROSOPHILA
Growers typically see relatively lower SWD populations in tunnels while enjoying options that are not possible in the field. Harvesting at least every other day and more thoroughly — made possible because of no weather interruptions — helps to decrease SWD numbers.
Landscape fabric placed over bare ground reduces dust. The fabric also makes it easier to spot and clean up dropped fruit.
Also of potential benefit are combinations of plastic, harvest interval, and insecticidal sphere treatments, Demchak says.
Some growers are using exclusion netting. “It does work,” Demchak says, “but it tends to increase temperatures and also blocks air flow.”
Demchak recommends dropping postharvest temperatures as close as possible to 32°F. Growers can use Entrust (Spinosad) and Pyganic (pyrethrins), she says, although they are not ideal solutions in high tunnels. The future release of parasitoids is promising.
TWO-SPOTTED SPIDER MITES
What growers do not want to see, Demchak says, are popula-tions of TSSM getting to the point in which webbing is visible.
“That tells you that the spider mites are trying to disperse,” she says. Flare-ups can be treated with a broad-spectrum insecticide such as Pyganic, Demchak says. However, the treatment can be hard on beneficials, she adds, and there are even indications that such pesticides may cause TSSM to lay more eggs.
Predatory mites have worked for Demchak against TSSM.
“As long as we release them early in the process, where we’re just starting to see damage, and we treat them well, they work well for us,” she says.
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