MN Fruit & Vegetable IPM News - Vol. 4, No. 5

Strawberry growers in southern Minnesota started picking this weekend. Some strawberries fields in northern Minnesota are just starting to bloom. Insect pressure is waning, even in northern Minnesota. I have found almost no fields with tarnished plant bugs in sprayed or unsprayed fields. Clipper weevils have stopped feeding and laying eggs in most of the state.

During harvest, you and your customers will be assessing your disease control practices. In most years, gray mold is rare. Fungicides, narrow rows and straw have kept gray mold outbreaks to a minimum in the last decade. Gray mold is reported more often that it occurs, because gray mold can be confused with other diseases. Many people confuse gray mold and slime mold.

Slime molds are primitive organisms that live on straw or on the surface of the plants. In Minnesota, I have found two distinct types of slime molds. One makes large, white masses on the leaves and straw (Photo on upper left). Another makes small gray spots on petioles or leaves (Photo on upper right). Both types will grow on the fruit, if the fruit is in the way. Both are harmless organisms that move slowly through the field. A kid who accidentally steps on the strawberry row will damage more fruit than slime molds.

Gray mold spreading through a cluster

Slime molds are not related to the fungi that cause gray mold. According to scientists, slime molds and gray mold are as distantly related as mountain lions and dandelions. Slime mold isn’t a disease, because it does not grow inside the plant tissues. Anybody who has eaten a strawberry with gray mold can taste the mold inside the berry even if the berry has no mold on the surface. Peel the skin off a berry with slime mold, and the berry should be fine.

Although slime molds are harmless, customers don’t like them. Fungicides do not control slime molds, because slime molds are not fungi. A few people have resorted to spraying the plants with chlorine, which is impractical in large fields. Some growers have successfully made up harmless stories about the white stuff in the field. Before going out and spraying a fungicide to keep gray mold from spreading, make sure that you are looking at gray mold and not a slime mold.

Table 1: Pests during the week of June 4 – all fields were between 5% and 80% bloom
Fields Monitored	Fields sprayed previously	Fields with tarnished plant bug nymphs	Fields with thrips	Fields with Clipper
14	6	2 (0 above threshold)	11 (0 above threshold)	5

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 June, 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.