A New Pest in the Vineyard — What to Watch For

I’m one of those wine lovers who prefers a face-to-face at the local bottle shop to a blind purchase online. My other preference is to order directly from a few trusted Swiss producers. This allows me to avoid the middleman, gives me time to talk things over with the winemaker, and puts me first in line to secure rare items not normally available to the dilettante. I rarely roll the dice with wine and it’s even rarer that I succumb to an overly enthusiastic sales pitch.

Recently, however, I was seduced by an online “flash-sale” from a single producer in Aargau who promised an “exploration” of Swiss terroir in the form of three identically made pinot noirs from three different villages. It sounded intriguing enough, so, for a reasonable 90CHF (shipping included), I plumped for two bottles of each cru. Even though the winery was new to me, it seemed like a low-risk proposition with the potential for a big payoff.

Wrong!

From a pleasure standpoint, it was a huge mistake to be so trusting. From a live-and-learn standpoint, it wasn’t all bad. I ended up learning a few things: chiefly — pungent green odors are not always what they seem.

Winning from losing, so to speak.

There’s no need for me to out the winery in question because quality judgments are not the subject of this piece. Instead, this is about the opportunity to investigate a perceived problem, how one thing leads to another, and how reasonable conclusions flow from a methodical accumulation of evidence.

When Green Goes Rogue

The first thing I think of when a wine is excessively green is that it’s produced from underripe grapes. That’s usually a good assumption, but not in this case. 2018 will go down in history as one of the best vintages ever in the Confederation with ripeness levels across all varieties and regions at near ideal levels.

In other words, you had to be an idiot not to work with ripe fruit in 2018.

As we all know, a certain amount of greenness is an attribute — think sauvignon blanc or cabernet franc. Subtle green aromas add freshness to some wines, as they do in a whole bunch-fermented pinot noir or syrah. And who doesn’t like the appetizing savory elements that herbal accents bring to an otherwise fruity wine? It’s only when green goes rogue, when it masks everything we like about wine that we begin to think beyond mere ripeness levels.

My first whiff of the most flagrant flash-sale offender offered a vague sour cherry aroma dominated by steaming compost. And it wasn’t just a fleeting smell, it loitered in the glass like cheap cologne on an unwashed adolescent. Indeed, it was a warlock’s mix of jalapeño pepper, noxious weeds, mildew, and singed hair. Tasting it was like tasting the wine equivalent of a redacted transcript where the blacked-out portions correspond to the pleasing parts of the wine.

It was then that I began to consider a nasty taint as the culprit. I reached for my handy copy of Flawless — Understanding Faults in Wine by Jamie Goode for some possible clues. In Chapter 13, Greenness in Wine and Ladybug Taint, I found below the sub-heading Brown Marmorated Stink Bug (BMSB or “the bug”) this description:

“It (the bug) produces a musty, coriander/cilantro aroma in wines, particularly reds, and is an increasing problem in many wine regions . . .”

Including Switzerland?

Bingo!

It was exactly the trans-2-decenal of coriander/cilantro I smelled and not the methoxypyrazines of green pepper. I began to imagine, to my horror, that I could smell and taste the bug itself, in all of its greasy grittiness. Yuck.

I contacted Dr. Goode via Twitter and asked him if he had ever tasted a wine tainted in this way. He said he hadn’t, but he put me in touch with Dr. Belinda Kemp, senior scientist at the Cool Climate Oenology and Viticulture Institute at Brock University in Canada, who kindly supplied me with the some of the latest BMSB research. Turns out, there isn’t much of it.

The key study on the topic is quick to mention cilantro as the prevalent scent analogue in wines tainted with trans-2-decenal. This is the stress compound released by the bug when it’s crushed or sufficiently agitated. Further study indicates that as few as three bugs per cluster can taint the finished wine. That’s not a lot of room for error, especially when one is unaware the bug even exists.

Armed with a new hypothesis, I now needed to place the bug at the scene of the crime in Aargau.

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BMSB living the life deep within a grape cluster (Photo: Penn State University)

Meet the Bug

The brown marmorated stink bug is native to East Asia where it is an agricultural pest of significance. It is held more-or-less in check by its natural enemy, the samurai wasp (Trissolcus japonicus). The aptly named wasp parasitizes the eggs of its host until the whole ecosystem achieves homeostasis. Unfortunately, the bug migrated to the U.S. in the mid-nineties without the wasp in tow. It spread unchallenged from its new home in Pennsylvania to most of the other fifty states. On its own, it scatters rather slowly, but, in a pinch, it will hitch a ride in whatever cargo it can find. That’s why most infestations are in urban areas where the bug likes to overwinter in the cracks and crevices of our homes. 

I know first hand. The bug has spread to Geneva where it is an occasional visitor to my office on a nice day when the outside door is left open.

The pest is particularly troubling because of its appetite for a wide variety of fruit, vegetables, and ornamental plants. It’s an equal opportunity pest. It damages crops by sucking them dry, leaving behind deformed fruit with a distinctive cork-like blight. A significant infestation can lead to diminished quality, reduced yields, or total decimation.

While grapes are not a preferred host they are among the last crops available to the bug before its winter hiatus. BMSBs are commonly found wedged into grape clusters where they find juice, sugar, and warmth from the evening chill near harvest time. If they are not discovered and removed before fermentation and pressing they can taint the finished wine with the noxious odor described above.

Ground-Zero in Europe

The European version of BMSB was first discovered in 2007 and was most likely a direct transplant from Asia. We know this because it surfaced in Zürich after the renovation of its renowned Chinese Garden. Roof tiles used in the renovation and manufactured in China came from a factory with a significant BMSB infestation.

The Chinese Garden is a mere fifty kilometers from Aarau, the cantonal capital of Aargau.

Things are beginning to add up.

The next piece to fall into place further supports my thesis. In 2012 the first report of crop damage in Europe caused by the bug occurred in a hothouse pepper crop in Aargau. Since then the bug has decimated apple and pear crops in Zürich, vegetable crops in Germany, and tainted hundreds of thousands of gallons of wine in the Veneto. It is found in several countries in Europe but maintains its presence in and around Zürich and Basel. Aargau lays directly between the two.

Even more damning is that Aargau’s peak BMSB infestation occurred in the summer of 2018 — the very vintage in question.

That’s it. That’s my case.

As a relatively new introduction, reports of damage to wine are rare. There are no newspaper accounts or online features to rely on. There is a bit of research on the bug as a crop pest but very little as to its impact on wine. Thus, there are very few people with enough experience to discern the taint and to determine its cause. That includes me, which is why I emphasize that my conclusions are just a guess.

I have to say, however, I’m intrigued by the trail of evidence.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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