by Melissa Piper Nelson
Researchers from across disciplines and regions are cooperating to track and control the pesky brown marmorated stink bug (BMSB), Halyomorpha halys (Stal), which is finding a comfortable home in vineyards across the U.S. The annoying little brown bug which has invaded our lawns, gardens and homes for the past few years is now lodging itself in both grape foliage and grape clusters causing damage to crops and tainting juice and wine.
Just how much trouble the bug is actually bringing to grape growers and winemakers is still under investigation, but the pest is showing up in vineyards from the Mid-Atlantic to the West Coast and from north to south U.S. grape growing regions as well.
Penn State Research Technologist Jody Timer reporting in a recent Penn State wine and grape blog says the pesky insects “seek the moisture, sugar, and warmth on the inside of clusters and often migrate to the cluster’s interior close to harvest.” So along with the harvested grapes comes a little stinky surprise, which can get processed along with the grape crop. Timer says an initial study with colleagues concluded that while batches of juice with up to 25 BMSB per lug (35 pounds of Concord grapes) can be detected by tasters and are “sufficient to induce a perceivable flavor change in Concord grapes, a level of BMSB which would cause consumer rejection wasn’t reached,” at least in Penn State studies at present. But at what level would the taint hurt grape juice and wine production? That is the million dollar question researchers and producers are concerned with, especially as BMSB populations continue to increase and find vineyards and specialty crop plantings ripe for invasion.
The good news may be although the BMSB secretes volatile compounds into raw juices (some researchers liken it to a profound cilantro flavor) the fermentation process may make stink bug “yuck” no longer detectable. The bad news is the damage the pest inflicts on grapes, which some researchers believe can lead to plant rot and infections. Taint in wine grapes remains a debated issue with some winemakers identifying discernible off-tastes, while others point to university studies where processing negated the effect of any bugs crushed during harvesting and processing.
The BMSB, which gets its common name from the odor produced when the bug is crushed, has been identified as an invasive species originating in Asia, most likely China, Japan and Korea, according to integrated pest management (IPM) researchers. Possibly traveling to the U.S. in overseas shipping containers about 13 years ago, reports from the Stop BMSB organization (a cooperative scientific research effort) note the pest “has now spread to 41 states and Canada.”
Problematic to crops in the Mid-Atlantic in 2010, Timer reports the appearance of the pest in the Lake Erie grape belt “has the potential to become problematic.” And after the invasive pests also were found in Williamette Valley towns, Oregon vineyard managers are now monitoring for impacts in that grape-producing region. Researchers in Maryland and Virginia, where there are clusters of farm and boutique wineries, are taking the pest seriously, too.
Agricultural researchers have identified the BMSB as a serious pest in a variety of crops which moves among wild and cultivated host plants. Both Mid-Atlantic and West Coast studies have shown vineyards close to other agricultural crops and orchards may see more BMSB populations in late summer or when other host crops are harvested. BMSB can leave necrotic spots on berries, and in some instances, infect grapes with rot after puncturing and sucking out some juices. Damage has been found on both red and white grape varieties. Some studies also indicate lower berry counts and cluster weights with BMSB vineyard invasions.
While much has been learned about the BMSB over the past decade, the economic implications to grape growers and winemakers are still uncertain. Researchers know the pest can devastate other crops such as apples and peaches, and fear that numerous vegetable and specialty crops are vulnerable as well. In 2010, BMSB damage to the Mid-Atlantic apple crop topped $37 million. Says Timer, “There is considerable variation in the price of different cultivars of wine grapes,” so establishing economic impacts is difficult. In Oregon, test plots in Pinot Noir vines are designed to identify what the bugs are attracted to and what economic impacts might cause wine grape growers, a concern felt across the country.
In a BMSB report the Minnesota Department of Agriculture noted, “The brown marmorated stink bug prefers fruits as a food-source, but will feed on nearly all plant parts. Injury caused by feeding produces small necrotic areas on the outer surface of fruits and leaves. In apples, feeding by this insect creates cork-like dead spots that can become sunken and render the fruit unsuitable for market. All damage done is superficial and the fruit is safe to eat, however not preferred by consumers.” Tracking damage to tree fruits is easier to spot due to the indentations and bruising left on the fruit itself, but where stink bugs tuck into grape clusters, some damage cannot be detected until after harvest, according to Timer.
Getting rid of the pesky bug presents its own set of challenges. The bug is cold resistant and is a prolific reproducer. IPM studies reported in the IPM Practitioner have shown one female “can lay an average of 240 eggs per generation.” In the U.S., some areas have seen multiple generations in one year — in tropical regions, up to five generations are possible! And, as noted, BMSB are more difficult to detect in vineyards where they can disappear camouflaging into tight clusters or foliage.
Some recent integrated pest management techniques using parasitic wasps may show promise of keeping the BMSB at acceptable levels, and limited chemical as well as sustainable management efforts, especially along vineyard borders, may be beneficial as well. The stubborn BMSB, however, is still an invasive critter, which is being carefully monitored by grape growers and vineyard managers. And for those craft brewers who think stink bugs prefer grapes to hops, think again! Hops growers and specialty brewing crop producers are beginning to notice increasing infestations as well.
Even if fermentation and processing can obscure any taint the bug may impart to juices, the BMSB still has the potential to hurt crop production, a challenge the grape industry, not unlike the tree fruit industry, is diligently seeking to avoid at all costs.
For additional information on the BMSB, visit BMBS outreach informational outlets such as StopBMSB.org or contact your local cooperative extension for ongoing research and IPM resources.