MN Fruit & Vegetable IPM News - Vol. 2, No. 12

In this Issue:

GUEST ARTICLE

Are You a Producer or a Business Owner?

VEGETABLE NEWS

Vegetable Insect Update

STRAWBERRY NEWS

Strawberry IPM Update

APPLE NEWS

Weekly Trap Counts

Insect, Pest Fact Sheets

Vol 2 No.12

August 15 , 2005

Late Summer Foliar Diseases in Strawberries

Thaddeus McCamant, Specialty Crops Management Specialist, Northland Community & Technical College

August is an important month for strawberry plants. Leaves are starting to grow on the renovated strawberry plants and runners are starting to peg in on new strawberry fields. Plants start forming flower buds for next year. Although the plants are busy throughout August, strawberry growers can relax as long as their fields are fertilized, weeded, and watered. Strawberry growers should also look out for leaf diseases.

The three foliar diseases that cause the most problems in Minnesota are leaf spot, leaf scorch, and powdery mildew. Although all three diseases are most common in late summer, we saw outbreaks of each disease earlier this spring. Leaf spot and leaf scorch need rain in order to spread, but powdery mildew usually spreads during dry weather.

Leaf spot has a small spot with a white center. In the past, leaf spot was one of the most destructive diseases in strawberry, but most new cultivars introduced in the last two decades are resistant to leaf spot. Kent, Jewel and Honeoye, all are susceptible to leaf spot. In June 2005, leaf spot even infected the normally resistant cultivar Glooscap.

Leaf scorch is similar to leaf spot but the infected areas are usually purple, without a distinctive white center. Leaf scorch is caused by a different fungus than leaf spot, and the disease usually kills large sections of the leaf. Fungicides that control leaf spot may not control leaf scorch.

Powdery mildew causes the leaves to cup. In severe infestations, younger leaves will be stunted and older leaves will be killed. Powdery mildew symptoms are similar to potato leafhopper but infected leaves have a white powdery mycelium on the lower surface. There are no varieties resistant to powdery mildew.

Control

Scientists are still developing thresholds for controlling strawberry leaf diseases in late summer. Several scientists have been operating on the assumption that an outbreak greater than 30% will lower yields the following year. If your field has a history of leaf diseases, you may want to spray a fungicide in early August while the canopy is still developing after mowing. The hot, dry weather in recent weeks has helped powdery mildew spread in several fields and many fields are infected.

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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.

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.

The University, including the Minnesota Extension Service, is an equal opportunity educator and employer. ©1999-2005 Minnesota Extension Service, University of Minnesota. All rights reserved. Contact copyright@extension.umn.edu for information on reproduction or use of this material.