Stink Bug Closes In on Wine Country

New threat to winemaking identified in Calfornia's Sacramento, Yolo and Santa Clara counties

by Paul Franson
The brown marmorated stink bug’s marbled legs are one of its identifying features. Photo source: Penn State
Napa, Calif.—Sometimes it seems as though a new insect pest is announced every month. The brown marmorated stink bug (also known as BMSB or Halyomorpha halys), which already has become a threat to winemaking in the fast-emerging mid-Atlantic states, has established itself in parts of California and seems sure to pop up in Napa and Sonoma counties soon.

Chuck Ingels, farm advisor for the University of California Cooperative Extension in Sacramento County, which is infested with the bugs, discussed BMSB at a recent Napa Valley Grapegrowers’ Sustainable Viticultural Practices Seminar.

The BMSB can impact wine in a number of ways. First, it can damage grapes by piercing and feeding on the fruit, which can lead to increased susceptibility to bunch rots.

The distinctive odor excreted by the bug as a defense is trans-2-decenal and trans-2-octenal. It smells like fresh cilantro but to some observers, is “skunky,” “citrusy” or “piney.” It is apparent in fresh must, but different studies have disagreed on its impact in finished wines.

A study by Joe Fiola at the University of Maryland in 2010 found perceptible aroma in juice at levels of 5-10 bugs per lug, but no distinguishable taint in the juice after four months.

With 10-20 BMSB per lug, there was perceptible aroma during red fermentation but again no distinguishable aroma in the wine following fermentation and racking.

At Oregon State University (Tomasino et al., 2013 ASEV abstracts), they tested one bug per four clusters of Pinot Noir, one bug per two clusters and no bugs. They detected distinct aroma during destemming and pressing with bugs present, and the resulting wines contained more trans-2-decenal than the control. The infected wines were perceived as different from the control.  

Elizabeth Tomasino of the Department of Food Science and Technology at Oregon State University also has conducted BMSB research that will be published soon.

The bugs are also nuisances, as they gather in flocks in tasting rooms and wineries.

Where they’re found
The native of China, Japan, Korea and Taiwan in East Asia is a crop pest in its native range and now in the United States.

It was first found in the United States in Allentown, Pa., in 1996, but wasn’t identified until 2001. It’s a major nuisance pest in the fall and winter, when the insects gather in great numbers and seek shelter from the cold inside.

The BMSB was detected in California in 2014 and now is established in Butte, Los Angeles, Sacramento, Santa Clara, Sutter and Yolo counties. It has been intercepted in other counties as well.

The bugs first inhabit urban areas, then move to agriculture.

About 170 species are now known to host the stink bug, with others likely. The host plant crops include stone fruits (especially peach), pome fruits, berries, eggplant, tomato, okra, pepper, corn, beans, sunflower and grapes, though fortunately grapes aren’t the first choice of the bugs. However, harvest of nearby crops may force migration to vineyards. Concerned growers should trap and monitor vineyard edges.

They also live in many ornamental plants including butterfly bush, catalpa, Chinese pistache, elm, fruiting mulberry, holly, maple, princess tree (Paulownia), pyracantha, redbud, waxleaf privet, wisteria and especially the tree of heaven.

It often overwinters under bark and in other closed spaces.

A number of stink bugs are often confused with the BMSB. The adult BMSB is rust color with broad brown markings. It is 0.5-0.63 inches long with two white bands on its antennae, smooth “shoulder” edges, a banded abdominal edge extending beyond wings and has banded legs.

They can have three generations per year.

What to do about the BMSB
Commercial traps for the BMSB are available from AgBio Inc. These Dead-Inn Traps include grower models that are 48 inches tall and cost $30; professional models that are 24 inches tall and $20, and homeowner models that are 16 inches tall and $17.

Rescue makes pheromone traps (Rocket Trap) that sell for $17.

Various lures are available from AgBio and Rescue. There are two main types of lures: pheromone lures (USDA No. 10 and No. 20; Harlequin bug pheromones are nearly identical) and “Synergist” of methyl decatrienoate (MDT). There are best used in combination.

A field study by Leskey et al. in 2013 found high mortality on the day of application from Endosulfan (e.g., Thiodan), methomyl (Lannate), thiamethoxam (Actara), and bifenthrin (e.g., Brigade).

Fenpropathrin (Danitol) and dinetofuran (Venom, Scorpion) provided a strong anti-feeding effect for more than seven days.

Effective insecticides in lab provided only 60% average mortality in the field when applied in early July, 40% in August and 20% in September.

A 2015 Orchard Spray Bulletin from Cooperative Extension in Virginia, West Virginia and Maryland found these products have shown good effectiveness:

• Pyrethroids: Baythroid XL, Danitol, Warrior II, products containing permethrin (e.g. Pounce)

• Neonicotinoid: Belay

• Carbamate: Lannate

• Premixtures: Endigo ZC, Leverage 360

• Section 18 insecticides: Bifenture/Brigade, Venom/Scorpion 

Some of these insecticides are not recommended in California.

The 2015 Spray Guide for Commercial Vineyards from Cooperative Extension in Virginia, West Virginia and Maryland recommended:

• Third cover spray (pre-bunch closure): Scorpion 35 SL, Actara 25WDG, Assail 70WP, or Malathion 8F

• Fourth cover spray (after véraison: Scorpion 35 SL, Actara 25WDG, Assail 70WP, Venom 70, Belay 50WDG, or Malathion 5EC

• Harvest spray the day before harvest: Belay or Pyganic (organic) 

Again these are not recommendations for California.

Pennsylvania State University and Rutgers University have looked at alternative BMSB management.

They recommend border applications using strong residual products and treating surrounding vegetation if feasible.

One possibility is planting trap crops (like beans and Paulownia trees) and spraying them.

Organically acceptable insecticides that provide partial to fairly good control of nymphs only include Pyrethrum, Azadirachtin, Spinosad, Sabadilla, insecticidal soap and combinations.

The USDA is investigating biological controls. These include Gymnosoma par flies and egg parasitoids Trissolcus wasps. They may be released in California in 2016.

Other predators are assassin bugs, praying mantis and spiders.

Get more information at stopbmsb.org, ucipm.ucdavis.edu or cesacramento.ucanr.edu.

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