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AgAlerts 2004 From Griggs County
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Issue # 7, July 8, 2004
Conditions have been favorable for disease development in small grains. The disease forecasting model for scab on July 7th is showing moderate infection possibilities. See Map. The forecasting model for leaf diseases is much higher. See Table. With the current yield potentials, applying a fungicide is recommended.
The Steele County range tour will be held on Tuesday, July 13th starting at 9:30 am at the Hope Legion. Range and animal health specialists from NDSU Extension and NRCS will be conducting on site evaluations and grazing systems. For more information, contact the Steele County Extension office at 701-534-2253.
Brown
spot is a disease that is favored by wet weather. Symptoms of the disease
are small, dark brown, irregular spots with or without a yellow halo.
Lesions may enlarge and coalesce, and frequently they are concentrated along the
leaf veins or at the leaf margin. The disease decreases with warm, dry
weather. The past two weeks have been ideal conditions for this disease.
The following pictures show some of the symptoms of this disease. Notice
the leaf damage due to the break out of the diseased areas of the leaves.
There is no treatment for control of this disease other than crop rotation or
tolerant cultivars. Click on the following link for a picture of septoria
brown spot.
Downy mildew infections may appear in
sunflower in the next few weeks in areas where heavy rains and saturated soils
coincide with sunflower germination and emergence. The downy mildew fungus is a
"water mold" and thus is favored by recent weather. Systemic
infections by the downy mildew fungus result in stunted plants with yellowing
along the main veins on the upper leaf surface, and a downy white growth along
the main veins on the lower leaf surface. After the systemically infected plants
appear, secondary spread may occur if wet weather reoccurs.
Once downy mildew is present, nothing can be done to halt
development. Seed treatment with Apron used to be a very effective means of
control, until the occurrence of races resistant to this class of fungicide.
The amount of downy mildew present in any field depends on
what percent of the downy mildew population in that field is resistant to Apron
seed treatment, how wet the soil was before emergence, and how long the soil was
wet. Sunflower seed generally is still treated with Apron or similar product,
but the percent of the downy mildew population that is Apron resistant varies
considerably among fields, as shown by Dr. Tom Gulya, USDA sunflower
pathologist. Satisfactory substitutes for Apron seed treatment for control of
downy mildew are still not available, but Dr. Gulya continues to seek
alternatives. He has four seed treatment fungicide trials on sunflower this
year, located at Whapeton, Prosper, and two north of Moorhead. (Information
provided by Dr. Art Lamey)
(click on photos to enlarge)
Please Contact Our Office For Additional Information
E-mail: john.swenson@ndsu.edu
Go to the 2003 AgAlert Index Page
