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South Dakota Wheat Growers Can Use Fungal Disease Forecasting Tool

Bill Spiegel Updated: 06/05/2014 @ 8:50am I grew up in north-central Kansas, and am the Fourth Generation to maintain and manage our farm on which we grow wheat, soybeans and grain sorghum. I'm a 1993 graduate of Kansas State University in ag communications. I joined the Successful Farming/Agriculture.com team in 2014.

The winter wheat crop in South Dakota may have the greatest yield potential of any in the nation. Timely precipitation and good growing conditions have helped nurture the crop in the Mount Rushmore State, which has wheat specialists believing farmers should take steps to protect the crop from potential fungal diseases. As of May 27, the state’s winter wheat crop was rated 38% good to excellent.

Just in time for fungal disease field scouting, South Dakota State University has launched the “Small Grains Disease Forecasting” Web tool in conjunction with North Dakota State University to help producers decide whether a fungicide application is warranted.

The system – online here – uses weather variables to predict the likelihood of disease development. Already this spring, farmers are noticing tan spot and septoria leaf blotch lesions, says Bob Fanning, plant pathology specialist at SDSU’s Winner Regional Center. “We haven’t seen a huge epidemic so far, but I’d say the potential for those two diseases to occur is above average,” Fanning says.

Timely precipitation, plus plenty of humidity in central South Dakota has combined to increase the likelihood of fungal diseases, adds Ruth Beck, SDSU’s Extension cereal crop specialist. “Plus, many farmers use no-till, so producers seeding wheat into wheat stubble should watch fields closely and look for disease pressure,” Beck adds.

With dry weather toward the south, however, the rust complex does not appear to be a concern at this time, Beck and Fanning agree.

However, most leaf spot diseases, especially residue-borne diseases like tan spot, and Stagonospora/Septoria blotch will develop under wet and humid weather conditions, according to a news release from SDSU. Presence of dew on leaves for extended periods indicates an increased risk for diseases to develop; these are the conditions the state’s wheat growers are now facing.

The online forecasting system is designed to help wheat growers protect the top two leaves, which contribute the most to grain yield and to avoid unnecessary fungicide application if not needed. The small grains disease forecaster requires producers to follow three steps in order to determine the need to apply a fungicide:

  • Step 1: Establish the presence of disease in the lower leaves at the late jointing growth stage. Scout for leaf spots on the second leaf below the flag leaf (F-2 leaf on the main tiller) of at least 40 leaves at random stops. If half of the leaves have fungal leaf spots, proceed to the next step. Otherwise, scout again every three days.

  • Step 2: If there is enough incidence of fungal diseases, consult the model table, select the nearest weather station, the growth stage, and count the number of times “Yes” appears in the table. If the table has six to eight consecutive “Yes” infection periods, proceed to step 3. Otherwise repeat step 1 after three days.

  • Step 3: Check for weather forecasts. If rainy, humid weather is in the forecast in the next three to five days, consider applying a fungicide at the earliest convenience. Fungicides need at least two hours before any rain to avoid washout.

If conditions warrant a fungicide application, Fanning says wheat growers can apply product when the crop is at the flagleaf stage to get good protection from fungal diseases.

“Combination products that include both strobilurin and triazole modes of action can provide protection from leaf spotting diseases like tan spot and fusarium,” he says.

These options include Stratego YLD, TwinLine, Quilt 200SC, Quilt Ecel2.2 SE, Stratego 250 EC, and Absolute 500 SC. Diseases controlled depend upon rate and timing of application; also, keep in mind the preharvest interval of each product.

SDSU has more information about rates and efficacy here.

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