MN Fruit & Vegetable IPM News - Vol. 2, No. 15

The 2005 grape season is coming to a close in most of the vineyards in Minnesota and Western Wisconsin . Now it's time to watch the wine ferment and wait for a few months or years to drink the results of a season of hard but pleasant work. The end of the season provides a great opportunity to evaluate the monitoring and control methods used to manage the most important insect pests of wine grapes in Minnesota , including grape flea beetle (GFB), grape berry moth (GBM), and the multicolored Asian lady beetle (MALB).

GFB is an early-season pest that feeds on buds from bud swell until the first leaf separates from the shoot tip. Once shoot growth reaches 3 inches, damage caused by the GFB normally does not affect yield. Vines on the borders of the vineyard, next to wooded areas, will likely have higher infestations. Cultural control measures include removal of debris and leaf litter on the edges of wooded areas and wasteland located near vineyards to eliminate overwintering sites. Scouting is done by sampling throughout bud swell stage (twice a week) for damaged buds and flea beetles. If 5% of the buds are damaged, insecticide should be applied. Chemical control of GFB can be done with Imidan (phosmet), Danitol (fenpropathrin), Kryocide (Cryolite), Sevin (carbaryl; also controls cutworms), Thiodan (endosulfan; also controls the foliar form of phylloxera).

GBM is present in the vineyard throughout the growing season but larval activity and feeding late in the season on ripening berries causes yield loss and, if the population density is high, economic losses may occur. GBM adults are monitored efficiently with pheromone traps. In Minnesota , the use of insecticides to control this insect has not been required due to its low population densities.

Even though MALB is seen in the vineyard throughout the growing season, control measures are not justified until one or two weeks before harvest. There are several reasons why grape growers should not manage MALB earlier in the season. First, this insect cannot penetrate grape skins. MALB feed only 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 increases 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. Third, MALB is one the most abundant predators of insect pests in several other crops (e.g., soybeans, alfalfa, sweet corn) where they may contribute to reducing insect pest populations below economic thresholds.

During the 2005 growing season, we visited 5 vineyards weekly to collect data for the following objectives. Sampling plan for MALB: MALB population density was monitored using yellow sticky cards and visual sampling of clusters. These data sets will be used to develop sampling plans for MALB in grapes. Grape berry splitting: To determine the factors that affect grape berry splitting, we measured the soil moisture of these vineyards and collected soil and tissue samples for nutrient analysis. Sensory threshold for taint in wine: To establish a sensory threshold for the wine taint caused by MALB, laboratory studies are being conducted where grapes have been artificially infested with different levels of MALB adults and the subsequent wine made from these treatments will be evaluated for taint.

Based on our preliminary results, four weeks before harvest, growers should set up yellow sticky cards throughout the vineyard as an early-warning tool. Visual sampling of clusters should follow the yellow sticky cards and if high numbers of MALB are found in the clusters 1-2 weeks before harvest, insecticide should be applied. Our preliminary threshold is 0.5 beetles per cluster, but research is underway to determine if the threshold of MALB in clusters should be modified. Our small-plot insecticide trial and on-farm insecticide applications have shown that Sevin (carbaryl) is one of the best insecticide control options available at this time. Sevin is highly toxic to MALB and has a pre-harvest interval (PHI) of 7 days.

We would like to thank all the grape growers that cooperated with us in 2005 and we look forward to working with the grape industry in Minnesota and Wisconsin again in 2006.

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ACKNOWLEDGEMENTS

Co-Editors: Bill Hutchison (hutch002@umn.edu), Department of Entomology, University of Minnesota, Jeanne Ciborowski, Minnesota Department of Agriculture, Ag. Resources Management and Development Division, and Suzanne Wold-Burkness (woldx018@umn.edu), Department of Entomology, University of Minnesota

The Newsletter is published weekly from May through August, cooperatively, by the Minnesota Department of Agriculture (MDA) and the University of Minnesota (U of MN). Reports are posted on the U of MN and MDA web sites on Fridays. If you have suggestions and/or comments, please send your contributions by 4 p.m., Wednesday to Jeanne Ciborowski, 651-297-3217, jeanne.ciborowski@state.mn.us , MDA, 90 W. Plato Blvd., St. Paul, MN 55107-2094. You can access the Newsletter at the U of MN web site in htm format at: www.vegedge.umn.edu/MNFruit&VegNews/mnindex.htm and at the MDA web site in pdf format at: www.mda.state.mn.us/biocon/fruitreports/

Partial funding for this publication is provided through partnership agreements with the Minnesota Fruit and Vegetable Growers Association (MFVGA) and the United States Department of Agriculture – Risk Management Agency (RMA). These institutions are equal opportunity providers.

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