MN Fruit & Vegetable IPM News - Vol. 4, No. 3

Fields in most of Minnesota are blooming. Tarnished plant bug nymphs are hatched and growing. Clipper weevils continue to be a problem, even in fields past peak bloom. Most fields have thrips, but at low numbers (less than one thrip per blossom). A frost on May 15 blackened strawberry blossoms in eastern Minnesota. Rains on May 23 and 24 will cause gray mold infection periods in fields that are blooming.

The difference in bloom date between early cultivars like Annapolis and late cultivars like Jewel are greater than normal this year. In some fields, peak bloom for the two cultivars will be 7-10 days apart. Growers with multiple cultivars will have to adjust their management practices to account for the variation in bloom time between early and late blooming cultivars. Monitoring for tarnished plant bug will be critical. For example, many people sprayed their fields for clipper weevils or leafrollers when the Annapolis were in early bloom. The clipper sprays should control tarnished plant bug in Annapolis, but you will not know if the spray helped varieties that bloom a week later unless you monitor.

To monitor tarnished plant bugs, walk through the fields and tap blossom clusters onto either a white plate or your hand. Tarnished plant bugs are usually concentrated in certain sections of the field, so you should cover each corner of the field. Tarnished plant bug nymphs go through five distinct stages or instars. First instar nymphs are small green dots slightly bigger than the period at the end of this sentence. They look like aphids, but move quickly, crossing your finger or hand in a matter of seconds. Fifth instar nymphs are a ¼” long, with small wing buds. First and second instar nymphs are so small they only stay on one blossom cluster. Fourth and fifth instar nymphs are large enough to cross blossom clusters. The best time to control tarnished plant bugs is when the nymphs are in their first through third instars. In my experience, fields with large numbers of fourth instar nymphs already have economic losses.

The economic threshold for your fields depends on both your comfort level and the age of the nymphs. If most nymphs are in their first or second instar, a threshold of one nymph per ten blossom clusters is advisable. If the nymphs are older, you can use a threshold of one nymph per four blossom clusters.

Table 1: Pests during the week of May 21
# Fields Monitored	Fields at 10% Bloom	# Fields with tarnished plant bug nymphs	# Fields with thrips	# Fields with Clipper
10	7	4	8	6

Return to index

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, 651-201-6217, jeanne.ciborowski@state.mn.us , MDA, 625 Robert St. North, St. Paul, MN 55155. 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/plants/pestmanagement/ipm/ipmnews.htm

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.

DISCLAIMER

Reference 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, 2007 by woldx018@umn.edu
The University, including the Minnesota Extension Service, is an equal opportunity educator and employer. Privacy Policy
©1999-2007 Minnesota Extension Service, University of Minnesota. All rights reserved. Contact copyright@extension.umn.edu for information on reproduction or use of this material.