In this Issue:
VEGETABLE NEWS
Vegetable Insect Summary for Minnesota - 2006: European corn borer and Corn earworm
GRAPE NEWS
Wine Grape Insect Summary for Minnesota and Northwestern Wisconsin - 2006: Beetles & Moths
STRAWBERRY NEWS
Fall Colors, Plant Health and Weed Control
APPLE NEWS
The USDA Cooperative Agricultural Pest Survey for Exotic Apple Pests in Minnesota
IPM PUBLICATION
New IPM Publication Series for Growers, Processors, Crop Consultants, & Extension Educators
| Vol 3 No. 12 | September 29, 2006 |
Fall Colors, Plant Health and Weed Control
Thaddeus McCamant, Specialty Crops Management Specialist, Northland Community & Technical College
Fall colors are important to Minnesotans. Newspapers give the most recent updates of fall colors on their front page. Websites direct people to areas with the prettiest foliage. Although most plants turn color in the fall, the weekly color reports only mention plants like maples and sumac while forgetting soybeans and crabgrass. Soybean leaves turn yellow, while crabgrass shows shades of purple. Many fruit growers will enjoy the bright reds on their strawberries and blueberries. For optimists, the brilliant colors of fall signal a time of celebration. For pessimists, the colors mean death. For fruit growers, the fall colors are an excellent example of recycling.
Leaves turn color during a process called senescence. During senescence, the plant takes nutrients, such as nitrogen and phosphorous, out of their leaves and stores those nutrients in other parts of the plants. When the leaf is robbed of its nitrogen, it slowly dies or senesces. Senescence differs from a sudden death from frost or mowing, because the plant is able to move nutrients before the leaf dies.
In annuals like crabgrass and soybeans, the entire plant senesces when the seeds begin to form. Annuals overwinter as seeds, so the protein coming from the leaves goes into the seeds. The stored protein is used when the seeds sprout next spring.
In woody plants and perennials, the leaves senesce in autumn. Strawberries move nitrogen from their leaves to the crown. Blueberries move nitrogen from the leaves to the bark. Using recycled nitrogen is more energy efficient than mining nitrogen from the soil. When strawberries sprout in the spring, nearly all the nitrogen the plants use come from storage reserves. Raspberry canes grow rapidly in early spring, relying almost exclusively on stored nitrogen.
For farmers, senescence in September and October is a sign of healthy plants. Soybeans that properly senesce have higher protein than those whose leaves are prematurely killed by frost. Strawberries and raspberries whose leaves normally senesce are more winter hardy than plants whose leaves are removed by deer or diseases. The raspberry cultivar K81-6 proved unsuitable for Minnesota , because diseases killed its leaves in August, and the plants were stunted the following spring.
Farmers can use their knowledge of senescence to control weeds. Most pigweed and crabgrass start senescing in early September. Controlling annual weeds in the fall is typically ineffective, because the plants are already dying and the seeds are already forming. Perennial weeds like Canada thistle, musk thistle and quackgrass usually senesce in October. Fall is the best time of year to control perennial weeds with either herbicides or tillage, because plants are vulnerable before they senesce. Perennial plants readily absorb Glyphosate (Roundup) this time of year, and store it with nitrogen. If you pull thistles this time of year, the weeds will be much smaller next spring, just like the raspberry plants whose leaves died in August.
From a strictly scientific point of view, the pessimists are right: fall colors are a sign of death. Fruit growers can look at the fall colors as sign of renewal, knowing that their plants are healthy and ready for winter. Fall colors also mean that the year's work is nearly done, and that fruit growers can finally rest. For me, even the soybean fields look pretty this time of year, but I do draw a line when it comes to crabgrass. Crabgrass is always ugly in a berry field, even when it turns purple.
 Blueberries and raspberries in October |
 Grape leaves senescing. The oldest leaves die first, followed by younger leaves. Senescence isn't always pretty. |
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 Jean Ciborowski, 651-201-6217, jeanne.ciborowski@state.mn.us, MDA, 625 Robert St. North, St. Paul, MN 55155-2538. 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: http://www.mda.state.mn.us/ipm/ipmnews/
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
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The University, including the Minnesota Extension Service, is an equal opportunity educator and employer. ©1999-2006 Minnesota Extension Service, University of Minnesota. All rights reserved. Contact copyright@extension.umn.edu for information on reproduction or use of this material.