Scouting Tips For Growing Grape Pest Threat

Grape growers should be on the lookout this fall for two pests that are popping up in vineyards along the West Coast.

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The brown marmorated stink bug (BMSB) and the spotted wing drosophila (SWD) were almost unknown quantities in vineyards a few years ago, but their presence is a concern among those in the grape and small fruit businesses.

The stink bug, in large enough quantity, has the potential to taint wine. And while SWD hasn’t had much impact on grapes, there is a possibility it could damage some injured grapes and has posed a threat to berries, cherries, and other small fruits.

Stink Bugs

Known more for infestations in the East, BMSB has started building population in the west for the last few years. At the moment, it hasn’t caused too many problems in grapes. But Doug Walsh, integrated pest management coordinator at Washington State University, says the impact came fast in other places, and the West Coast should be ready.

“The experience they had in the Northeast was it took several years to notice they even had it, then there was a lag time before it hit biblical proportions,” Walsh says. “We’re finding the insect on a consistent basis at a relatively low abundance. We’re kind of in that lull time where we’re noticing it. We’re kind of in a wait-and-see pattern.”

Studies conflict on whether BMSB can taint wine, but Walsh says he’s heard that less than one bug per 10 liters of wine can be detected, causing concern that a significant uptick in population could be problematic.

Gwen Hoheisel, a regional Extension specialist at Washington State University, says that operations with a wide variety of crops should be especially watchful.

“The more diverse you are, then you can have some more damage because the stink bug can have more hosts. It can move from host to host,” Hoheisel says.

Walsh and Hoheisel suggest beating sheets or visual inspections to check for the presence of BMSB.

The bugs are difficult to tell from other species of stinkbugs, but according to the website stopbmsb.org, there are some differences that will help discern it from lookalikes:

  • BMSB’s underside is brown-gray in color. Brown stink bugs have a yellowish-green underside.
  • BMSB has more rounded shoulders compared to the spined soldier bug, which has  sharper, acute shoulder angles. The spined soldier bug also has a shorter, thicker first segment of the proboscis and more reddish antennae.
  • The dusky stink bug also has more pointed shoulders and is generally smaller than BMSB.
  • The rough stink bug has a small point on each side of its face, and its shoulder area, just behind the head, has a rough row of spines. BMSB has neither of these.

If a fruit grower suspects BMSB, Hoheisel suggests contacting a local Extension office. She says there are no treatments yet, but Extension specialists are tracking the bugs. Walsh says running an air blast sprayer through the vineyard ahead of a mechanical harvester can help knock them off vines.

“We found that to be effective with the lady bird beetles,” Walsh says. “I haven’t done research with stinkbugs, but I think it would help quite a bit.”

Walsh added that a parasitoid for BMSB has been found, offering hope for a biological solution, but that isn’t a control option at this point.

SPOTTED WING DROSOPHILA

The spotted wing drosophila has been a significant threat to berries, cherries and small fruits for several years. The pests are especially prevalent in areas that have moderate winters where SWD can survive year round.

Females have ovipositors with teeth that pierce the skins of fruit. Larvae grow inside and spoil ripe fruit.

“SWD can go into fruit that isn’t split or overripe,” Hoheisel says.

For grape growers, there’s not a lot of concern, she says, because the skins of grapes grown in the West are too thick for SWD.

However, Walsh says, there is a chance that damaged or split fruits could get some SWD. In tests of damaged fruits, SWD was only 10% of the types of fruit flies found, but he warns that growers should still be vigilant.

“If a fruit is injured by a bird peck or a mechanical abrasion, say from wind rubbing the fruit against the cordon, then that does become a site of attack,” Walsh says.

Growers can use apple cider traps to check for SWD. According to spottedwing.org, SWD can be identified by these attributes:

  • Males have double stripes on the tarsi of their front legs, the leading edge of their wings have a dark spot, and they have unbroken abdominal bands.
  • Females have a large, saw-like, serrated ovipositor with two even rows of teeth that are much darker than the rest of the ovipositor.

If a grower finds SWD, Walsh and Hoheisel suggest contacting the local Extension office for tips on crop treatment, which vary by location and crop. They also say early harvesting, where possible, can reduce the threat of crop damage since the insects are more prevalent in the later fall.