In this Issue:
GUEST ARTICLES
Why Use High Tunnels in minnesota?
USDA-Farm Service Agency County Committee Election
VEGETABLE NEWS
STRAWBERRY NEWS
Using Computer Models to Time Fungicide Sprays in Strawberries
APPLE NEWS
Weekly Trap Counts: June 27 - July 7, 2005
REMINDER: Apple Maggot Emergence Has Begun
| Vol 2 No.9 | July 11, 2005 |
Using Computer Models to Time Fungicide Sprays in Strawberries
Thaddeus McCamant, Specialty Crops Management Specialist, Northland Community & Technical College
In the last few months, the Minnesota Department of Agriculture and the Specialty Crops Management Program have been testing computer models for strawberry gray mold and powdery mildew. We used computer models developed for grape Botrytis and grape powdery mildew by Spectrum Technologies, because models developed specifically for strawberry Botrytis (gray mold) and powdery mildew have not been developed.
The computer models for Botrytis and powdery mildew combine temperature data with leaf wetness to determine if weather conditions could cause a disease outbreak. Leaf wetness is measured by an instrument that calculates leaf wetness from a scale of 0 (dry) to 14 (covered with water).
| Table 1. Botrytis risk in June, 2005 in central Minnesota according to computer printout | |||||
| Date | High Temp |
Low Temp |
Wet (Hours) |
RH>95% (Hours) |
Daily Risk Warning |
| 6/10 | 76.0 |
55.9 |
11.0 |
13.8 |
0.16 = Low Infection Risk |
| 6/11 | 77.4 |
53.8 |
10.3 |
16.0 |
0.73 = Moderate Infection Risk |
| 6/12 | 83.0 |
55.2 |
0.0 |
3.5 |
0 = No Infection Risk |
| 6/13 | 67.7 |
54.5 |
12.5 |
23.5 |
2.53 = High Infection Risk |
The computer models help take the guesswork out of timing fungicide applications. For strawberry gray mold to occur, the leaves must be wet for over twelve hours when the temperature is at 70° F. The computer model adjusts the risk warning as the temperature rises or falls. The programs state specifically if the infection risk was low, moderate or high during a wet cycle.
Five strawberry farms throughout the state used the disease models this past growing season. In southern Minnesota, the program showed no gray mold weather until 60% bloom, which allowed strawberry growers to skip the first fungicide spray. The growers who sprayed according to the program had no gray mold in their first picking. Central and northern Minnesota had gray mold infection periods throughout bloom, and several growers sprayed fungicides three times.
Table 2. Powdery Mildew Infection Periods* in June 2004 and 2005 |
||
| Location | 2004 |
2005 |
| Afton | 4 |
9 |
| Wadena | 0 |
4 |
| Hinckley | 2 |
6 |
*Heavy ascospore infection |
||
Powdery mildew is usually a problem on first year plants during late summer. This year, according to the grape powdery mildew model, the number of infection periods before bloom increased dramatically over 2004. Powdery mildew and other leaf diseases did become a problem in many fields throughout the state in June. Many people sprayed specifically for powdery mildew, while others controlled powdery mildew with their gray mold or anthracnose sprays.
Conclusion: The grape powdery mildew and Botrytis computer models can help strawberry growers time their fungicide sprays for maximum disease control.
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.