How Many Stink Bugs to Ruin Wine?

Maryland specialist offers grapegrowers advice to reduce taint from new vineyard pest

by Linda Jones McKee
BMSB brown marmorated stink bug
Increased presence of the brown marmorated stink bug was discovered along the central Eastern Seaboard.
Keedysville, Md. -- How many stink bugs does it take to make a wine stinky? That was a question which, until recently, no one on the East Coast (or elsewhere) knew the answer to -- or even thought to ask. As long as stink bugs in vineyards were the native varieties, they were not a problem: Native species don’t feed on fruit such as grapes.

 Concerns about stink bug taint have grown, however, with the increased presence of the brown marmorated stink bug (BMSB) from China discovered in vineyards and orchards from Pennsylvania through West Virginia and Maryland and into northern Virginia.

 Dr. Joe Fiola, extension specialist in viticulture and small fruit at Western Maryland Research and Education Center in Keedysville, Md., did some testing in the past several weeks to determine how many bugs it takes per lug to affect the aromas and flavors in juice samples. He added controlled numbers of the BMSB to juice from 25-pound lugs of grapes and then evaluated the aroma of the juice.

“The smell added by the stink bugs is a crushed cilantro smell,” Fiola told Wines & Vines. “I could detect it at five bugs per lug; and at 10 bugs per lug, there was no doubt about the off-aroma.” Other descriptors used for the stink bug taint are “skunky,” “citrusy” and “piney.” At low levels, these aromas may not make the resulting wine unusable, but they may reduce a wine’s varietal character sufficiently that the wine would have to be used in a blend rather than bottled as a varietal wine.

The impact of stink bug taint on wine will not be determined until the inoculated wine has completed fermentation and been made into finished wine.

 What can grapegrowers do if BMSB has invaded their vineyards? While little research has yet been conducted on stink bug control, fruit orchards have been hit by this pest as well, and they have more experience with different control measures. Unfortunately, many agricultural chemicals do not have much, if any, activity against stink bugs, and those that do work seem to have only short-term effects.

 According to Fiola, however, some products including pyrethrins and pyrethroids are effective and have a short pre-harvest interval (PHI). Pyrethrin is a natural product with a short residual life; pyrethroids are synthetic compounds that are similar in both structure and mode of action to the pyrethrins, but were designed to have a longer residual life. While both chemicals may knock down the stink bugs, probably neither will keep high populations of BMSB from reinvading a vineyard. These chemicals, though, may eliminate the bugs that are present if applied just before harvest.

The simple method for removing stink bugs is to hand-harvest and eliminate any bugs as the grapes are cut from the vine, then to use a sorting table to remove any additional BMSB before the grapes are put in the crusher-destemmer. Some growers have suggested shaking the vine before picking, but that method may result in the loss of grape berries as well as the bugs, if the fruit is fully mature. Quality control for machine- harvested grapes is much more difficult.

The following table gives some possible insecticides that can be used against BMSB close to harvest. More information on the brown marmorated stink bug is available at Dr. Fiola’s “Timely Viticulture” website.
BMSB insecticides
*Pyola also relies on a Canola oil ingredient to smother the pests and has a much lower pyrethrin content, so it may not be as effective on BMSB.
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