MN Fruit & Vegetable IPM News - Vol. 1, No. 4

Strawberry bud weevil (SBW), also known as “clipper,” ranks as the number two insect problem in Minnesota strawberries (Minnesota Strawberry Growers Survey, 2001). Although infestation is not as widespread as tarnished plant bug in Minnesota, it is capable of causing economic injury in some strawberry fields.

Biology

SBW overwinter as adult weevils in fence-rows and wooded areas. Once temperatures reach 60 ° F, they move to nearby early budding plants such as strawberries. In Minnesota, SBW adults may start appearing in strawberry plantings as early as mid-May (approximately 100 DD base 50°F). They feed on the immature pollen of the blossom buds and the females deposit eggs in the buds. SBW girdles the bud and clips the stem, causing the bud to hang down or fall to the ground. In about a week, the egg hatches into a white, legless grub. The larva develops inside the bud, reaching maturity in three to four weeks. Pupation occurs in the soil and adults emerge in late June through July. After feeding on the pollen from various flowers for a short time, the new adults seek hibernating sites and remain until the next spring. Only one generation of SBW occurs per year in Minnesota. Clipper weevils move across the field at the very slow rate of 30 feet per season, which means that after three years, a clipper infestation can usually only extend 90 feet into a new planting.

Damage

The adult female clipper punctures blossom buds, deposits an egg, girdles the bud, and proceeds to clip the stem, causing the bud to hang down or fall to the ground (see image, left). Injury is most common along edges of fields near woodlots.

Management

Monitoring: Strawberry bud weevils are small and hide in the strawberry canopy; therefore most people monitor the number of clipped buds. Monitoring should begin in early spring and continue until bloom. The traditional treatment threshold is 1 clipped bud per 2 ft of row. However, new research data have indicated that a more accurate threshold is 6 clipped buds per three feet of row, or roughly four times higher than previously thought. Scientists have shown that remaining flowers will grow larger than expected and overcompensate for the clipped bud. ( New York State Pest Management Guidelines for Small Fruit Crops, 2001).

Control

Biological and Cultural Control: In most years, clipper weevil populations in one and two year fields are below economic thresholds, and therefore do not need to be sprayed.

• Some varieties, such as ‘Jewel’ can compensate for injury.

• Immediately plowing under old beds following harvest with removal of leaves and mulch may help by reducing the overwintering habitat of the weevil.

• Regularly rotate fields out of production so that there are few fields in production for more than three picking seasons.

Chemical Control:

Treatment must take place when blossom buds first become visible in the crown and temperatures approach 65°F. Complete field treatment is recommended for older plantings with a history of high SBW pressure. However, a border spray may be sufficient in new plantings or in older plantings with low SBW populations. Refer to the web site above for more information on chemical control.

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ACKNOWLEDGEMENTS

Co-Editors: Bill Hutchison, Department of Entomology, University of Minnesota, hutch002@umn.edu
Jeanne Ciborowski, Minnesota Department of Agriculture, Ag. Resources Division,jeanne.ciborowski@state.mn.us
Suzanne Wold-Burkness, Department of Entomology, University of Minnesota, woldx018@umn.edu

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., Tuesday 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/default.htm

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

DISCLAIMER

References to products in this publication is not intended to be an endorsement to the exclusion of others which may have similar uses. Any person using products listed in this publication assumes full responsibility for their use in accordance with current manufacturer directions.

Last Revised May 27, 2004.
The University, including the Minnesota Extension Service, is an equal opportunity educator and employer. ©1999-2004 Minnesota Extension Service, University of Minnesota. All rights reserved. Contact copyright@extension.umn.edu for information on reproduction or use of this material.