In this Issue:

VEGETABLE NEWS

Striped Cucumber Beetle

Vegetable Insect Update

STRAWBERRY NEWS

Strawberry Sampling Data from MDA and Grower Cooperators

A Note on Pesticide Registration in MN

APPLE NEWS

Apple Scab Infections

Weekly Trap Counts

Codling Moth Management

Apple Pest Activity

Insect, Pest Fact Sheets

Striped Cucumber Beetle

Eric Burkness, University of Minnesota

2005 Update: We have been monitoring SCB using a baited trap since April 15^th, but we have yet to see any beetles in our traps or on cucurbit plants. However, we expect to see SCB within the next 1-2 weeks. Based on an overwintering survivorship study at Rosemount, with 0% of beetles surviving winter conditions (see table), and below normal temperatures during May, we expect that populations of SCB may be low this year, and infestations to develop later than normal.

Seeded plantings in the Rosemount area are at the cotyledon growth stage. Newly emerging cucurbits are very susceptible to direct feeding damage, specifically cotyledon to the 3^rd leaf stages. In addition, at these early growth stages cucurbits are most susceptible to bacterial wilt (cucumbers and melons are generally more susceptible than squash and pumpkin), which can be transmitted by the beetles.

Table 1. Overwinter survival of SCB in Rosemount, MN 2004-2005
(Mario Carrillo, Robert Koch, Eric Burkness and Bill Hutchison, University of Minnesota)

Biology/Management: Striped cucumber beetle (SCB), Acalymma vittatum, is a major pest of cucurbits in the Midwest. Besides causing direct feeding damage on foliage and fruit, SCB also vectors the bacterial wilt pathogen, Erwinia tracheiphila. Adult SCB have yellow wings with 3 longitudinal black stripes. Proper identification of SCB is important because they are easily confused with western corn rootworm adults, which are not an economic concern in cucurbits. An easy way to distinguish between the two is to check the legs of the beetles. SCB adults have faint yellowish bands on the legs whereas western corn rootworm adults have solid black legs.

SCB can overwinter as an adult under debris in wooded areas and along fence rows adjacent to cucurbit fields. We do not yet know whether SCB can overwinter in Minnesota, or migrate into the state each year. After emergence, the adults feed on the blossoms of many alternate hosts such as hawthorn, dandelions, and many other indigenous plant species. Once cucurbit plants emerge, the beetles are attracted to cucurbitacin, a plant kairamone, to locate cucurbit plants. In Minnesota, SCB will not take flight until mean daily temperatures reach 65°F. Feeding and mating begin shortly after colonization of a cucurbit field. After mating, females begin laying eggs in the soil at the base of cucurbit plants. Eggs hatch in about a week and larvae feed on the roots and underground portions of stems of the cucurbit plants. A second generation of adult SCB will emerge and begin to feed on foliage, flowers and fruit, if present. SCB hide in the soil around the plant, under clods of soil, or in cracks in the soil during the heat of the day.

Adult feeding is of particular concern when plants are in the cotyledon and 1^st-3^rd true-leaf stages. At this size, the plants are small enough that high populations of SCB can either defoliate the plants completely or girdle the stem. The action threshold for first true-leaf plants is when SCB populations exceed 2 or more beetles/plant on 25% of the plants. Monitoring should occur weekly until initial infestations are detected. Once beetles are present, monitoring should occur more frequently to allow for a comparison of populations to the action threshold, or to detect the presence of any bacterial wilt. Once plants are at the 2^nd or 3^rd true-leaf stage, monitoring efforts should shift from monitoring beetles to checking the defoliation level. Monitoring the defoliation level is much faster and still allows for the detection of bacterial wilt. A defoliation level of 25% can be used as an action threshold.

As plants grow beyond the 3^rd true-leaf stage, several cucurbits (cucumbers and pumpkins) can tolerate very high levels of defoliation. Once flowering occurs, SCB will usually move off the foliage and begin feeding on blossoms and pollen. This is more noticeable on the large flowering cucurbits like squash and pumpkin. Fruit or flower feeding does not usually become a yield concern. However, feeding on fruit may cause some cosmetic damage when high SCB populations are present in a field (e.g., on pumpkins in the fall). For more management options, refer to the VegEdge fact sheet at http://vegedge.umn.edu/vegpest/CUCS/scb.htm.

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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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