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AgAlerts 2009 From Griggs County
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Issue # 6, June 8, 2009
Tan spot has been detected in winter wheat across North Dakota. As this disease progresses from the bottom of the plant to the top it is vitally important that an early season application of fungicide is applied. Tan spot, caused by the fungus Pyrenophora tritici-repentis, is a major leaf spot disease of winter wheat in the Great Plains of North America. Tan spot symptoms usually appear in early April, but its effect on yield loss is greatest during grain fill when severe spotting reduces the photosynthetic area of the upper leaves. The most severe damage occurs from the boot stage to dough stage and is greatest on late tillers. Wheat kernels can also become infected causing red or pink smudge and black point. Severely infected kernels can result in significant down grading of seed quality.
Symptoms: Tan spot first appears on wheat leaves as small, tan to brown lens or diamond-shaped spots. Characteristic symptoms are elliptical to elongate spots that are tan colored, have a dark brown spot near the center and are surrounded by a yellow border. As the lesions increase in size, they tend to grow together, producing larger, irregular areas of dead tissue. When leaves are young and actively growing, the spots typically remain small. Where spots are abundant, leaves may yellow, giving the field an overall yellow cast. The lower, more mature leaves are infected first and the pathogen spreads to the upper leaves as the disease progresses. Prolonged wet conditions (24 hours or more) are favorable to tan spot development.
Control: Fungicide sprays are directed at
protecting the flag leaf for as long as possible.
Early control with broadleaf sprays and fungicides, with reduced rates
is the best option. Full label rates are applied to the flag leaf near Feekes
10.5 for maximum control of late season leaf disease development.
Foliar fungicides may be applied with aerial or ground equipment. Five
gallons of water per acre is recommended for air; ground application generally
requires 10-20 gallons water per acre. Quadris,
Headline, and Stratego are recommended for controlling Tan Spot.
Read and follow all label instructions.
(article by Melissa Misek, Griggs County Extension Summer Intern)
The NDAWN Center is short for the North
Dakota Agriculture Weather Network. It
is a series of 67 automatic weather stations distributed across ND and border
regions of surrounding states. Weather
data is retrieved daily, checked for accuracy, and made available every morning
on the NDAWN website.
Many data applications including summarization, mapping, and analysis are
available free of charge.
Numerous NDAWN applications use these temperature or growing
degree day (GDD) models to estimate crop growth stages and insect emergence
throughout the season. This management information allows producers to quickly
identify windows when chemical applications are recommended or when crops are
susceptible to disease or insects. They can better plan chemical applications
and field scouting for pests. NDAWN applications using GDD to predict growth or
development stages are available for wheat, canola, sunflower, sugarbeet,
potato, barley, and corn. Comparisons
can be made between GDD from the year that the station first became operable. The
following table is a comparison of GDD for corn from 2004 to 2009 using a May
10th planting date for each year.
| Accumulated GGD for Corn from May 10th to June 8th for the years 2004-2009 | ||
| Year | Average Daily Accumulation | GGD above or below normal for corn |
| 2004 | 7 | -99 |
| 2005 | 9 | -45 |
| 2006 | 13 | +68 |
| 2007 | 10 | -25 |
| 2008 | 9 | -50 |
| 2009 | 11 | -65 |
Other models can warn producers of
impending disease or insect infestations so that corrective action may be taken
at the optimum time to ensure maximum pesticide efficiency. Or they may indicate
no action is required thus reducing pesticide use. In both cases the results are
increased production, higher quality seed, reduced costs, and greater profit.
The Small Grain Disease Forecaster determines the risk of occurrence of Scab,
Tan Spot, Septoria, and Leaf Rust. White mold risk maps for canola are also
available. Other models predict the occurrence of Potato Late Blight and
Cercospora in sugarbeets before visible symptoms appear.
Irrigators regularly use NDAWN data to estimate daily crop
water use for their irrigated crops. This allows them to more efficiently
control irrigation applications. Over irrigation not only wastes water, but it
leaches nitrogen and other chemicals into the ground water. (article
by Melissa Misek, Griggs County Extension Summer Intern)
The NDAWN (North Dakota Agricultural Weather Network) has the small grains disease forecasting model is on line. This model uses weather data from the desired NDAWN site and determines if weather conditions are favorable for development of tan spot, spot blotch and leaf rust currently and as the season progresses fusarium and stem rust will be added. This data can be used to help monitor small grains for these diseases or to determine if a fungicide application is necessary. The following link will bring up the Small Grain Disease Forecasting Model. This site is easy to use. Just select the NDAWN station you would like to use and click "Get Data". A chart will show what the disease possibilities are for each site.
NDSU is an equal opportunity institution
Please Contact Our Office For Additional Information
E-mail: john.swenson@ndsu.edu
Go to the 2008 AgAlert Index Page