Wine Grapes in the Midwest:
Reducing the Risk of the Multicolored Asian Lady Beetle
Tederson L. Galvan, E.C. Burkness and W.D. Hutchison, Department of Entomology, University of Minnesota
Overview
Wine grape production
has increased significantly
in Minnesota and other
Midwestern states during
the past 20 years. Even
though the acreage of Minnesota
grapes is low (about
220 ac.), the high value
of the crop, ranging from
$4,000 to $7,000/ac, depending on the grape variety, has
increased its importance in Minnesota and enhanced the
diversity of agriculture and the economy. This growth
in the wine industry has been attributed to the releases
of new wine grape varieties, such as Frontenac and La
Crescent, which are more winter hardy, tolerating temperatures
as low as -30 °F. These varieties also are resistant
to plant diseases such as downy mildew and powdery
mildew. In the past, Minnesota and surrounding states
had not typically experienced problems with any particular
insect pest, but in 2001, wine makers began to notice
a foul taste in their wines.
The new taste resembled “burnt peanut butter” and
later it was found to be associated with the presence of
the multicolored Asian lady beetle (MALB), Harmonia
axyridis, which was found in the clusters during harvest
and wine processing. Since then, MALB has become an
economically significant contaminant pest of the winemaking
process. The beetles tend to aggregate on clusters
just before harvest, and subsequently, some beetles
may be incorporated with the grapes during wine processing.
Once crushed, MALB releases their foul smelling
hemolymph (insect blood) that can taint the flavor and
aroma of the resulting wine. Tainted wine and the unacceptable
taste associated with it has caused millions of
dollars in losses (unpublished data) to the wine industry
throughout the Eastern U.S. and Southern Canada.
Even though MALB can be observed in vineyards
throughout the growing season, control measures are not
justified until 1-2 weeks before harvest. There are three
reasons why grape growers should not manage MALB
earlier in the season. First, this insect cannot directly
damage, or penetrate grape skins. To date, MALB have
only fed on berries that have been previously damaged
by other insects, birds, diseases, or “splitting.” Although
berries can be damaged as early as the berry set stage, damage increases dramatically as the sugar content rises
over the last few weeks of ripening. Second, MALB is a
contaminant pest and its presence in the vineyard throughout
the growing season does not affect grape yield. Finally,
MALB is one the most abundant predators of several insect
pests, including pests of grapes, and in several other crops
(e.g., soybeans, sweet corn), where they may further contribute
to reducing insect pest populations.
IPM Approach
Sampling MALB in vineyards
As part of our research
in Minnesota, we found that
both yellow sticky cards and
visual sampling of clusters
were effective at detecting
the early arrival and buildup
of MALB infestations. Sticky
cards allow the grower to
monitor changes in the
MALB population, with minimal
sampling effort (cost)
and may help with the timing of control decisions. Based
on our preliminary results, four weeks before harvest,
growers should set up yellow sticky cards throughout the
vineyard (4-6 cards per acre) as an early-warning tool.
Direct, visual sampling of clusters during grape ripening
can then be used to provide a more accurate estimate of
MALB population densities. Research is underway to precisely
determine the optimum sample size and treatment
thresholds for MALB in clusters.
RESULTS
MALB densities were correlated with an increase
in the percentage of clusters with damaged berries (Fig. 1). Our results suggest that many of the MALB arrive
in the vineyard 2 to 3 weeks before harvest, and that
the increase in beetle density in clusters depends primarily
on the increase in clusters with damaged berries. Most
of the damage was caused by splitting that penetrates
deep into the flesh. Additional sources of damage were
birds, such as starlings, or black rot, and grape berry
moth larvae. Since MALB cannot cause initial damage
on berries, preventing or minimizing splitting damage to
berries should decrease MALB infestations on grapes.
Fig. 1. Multicolored Asian Lady Beetle (MALB) and the
timing (phenology) of related events; vineyard near
Hastings, MN, 2004.
IPM decisions before harvest: Chemical control if needed
Our insecticide trials have
shown that Sevin® (carbaryl)
is the most effective insecticide
available, based on a costbenefit
analysis. Plots treated
with Sevin resulted in 85%
of clusters being MALB-free.
Higher levels of control were
observed in larger vineyard
trials. This level of control
reduced the cost of excessive
washing of clusters or removal
of MALB, cluster by cluster,
which greatly hinders grape
harvest and processing.
Decisions after harvest & before wine processing
If MALB is present at harvest, beetles must be removed
by shaking clusters and covering bins where clusters are
held. Growers may also float
clusters in buckets of water
or vacuum clusters to remove
beetles. However, each
method has resulted in significant
increases in time and
labor, and increased the costs
of harvest (Table 1). According
to these estimates, based
on recent prices in Minnesota,
growers that use a pre-harvest
IPM strategy (sampling, or
sampling and a single spray),
for MALB in wine grapes
will save at least $200.00/ac
when compared with growers
that rely only on physical or
mechanical removal of beetles.
From 2003-2005, 78% of the
vineyards that we have monitored have had significant
infestations of MALB, making it likely that the use of IPM
will provide increased net returns and reduce the risk of
MALB infestations in the final product.
DISCLAIMER
Reference to products in this publication is not intended to be an endorsement to the exclusion of others. Any person using products
listed in this publication assumes full responsibility for their use in accordance with current manufacturer directions.
ACKNOWLEDGEMENTS
Funding for this series of IPM publications was provided by the USDA Risk Management Agency (USDA-RMA) in
cooperation with the Minnesota Fruit and Vegetable Growers Assoc., and the MN IPM Program (USDA-CSREES).
Research was supported by the North Central SARE, Minnesota Rapid Response Fund, and the MN Grape Growers
Assoc. For more information regarding this project or IPM in the Midwestern U.S., see the VegEdge Web site.
Citation: Galvan, T.L., E.C. Burkness, and W.D. Hutchison. 2006. Wine grapes in the Midwest: Reducing the risk
of the Multicolored Asian Lady Beetle. Public. 08232. Univ. of Minnesota Extension Service, St. Paul, MN.
