The South Dakota State University Small Grains Plant Pathology program has partnered with the Small Grains Plant Pathology program at North Dakota State University to deploy a small grains disease forecasting system for South Dakota.   

The system uses weather variables including rainfall, temperature, and relative humidity to predict the likelihood of fungal diseases development in small grains.

"In order for plant diseases to develop, they require three factors: the host (wheat), the pathogen, and conducive environment," said Emmanuel Byamukama, SDSU Extension Plant Pathologist.

He explained that the host and most pathogens are always present, the limiting factor then becomes the environment. "Most leaf spot diseases especially residue-borne diseases like tan spot, and Stagonospora/Septoria blotch will develop under wet and humid weather conditions," Byamukama said. "Presence of dew on leaves for extended periods indicates an increased risk for diseases to develop."

The overall objective of this forecasting system is to help the grower 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," he said.

Necessary Steps

The first step, Byamukama explained is to establish the presence of disease in the lower leaves at the late jointing growth stage. "Scout for leaf spots on the second leaf below 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," he said.

The second step - once there is enough incidence of fungal disease - is to consult the model table, select the nearest weather station, the growth stage, and count the number of "Yes" in the table. If the table has 6-8 consecutive "Yes" infection periods, proceed to the third step. "Otherwise repeat step one after three days," Byamukama said.

The third step is to 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," he said. "Fungicides need at least two hours before raining to avoid washout of the fungicides."

When using the forecast system for diseases like Fusarium head blight or scab prediction, Byamukama said the forecasting system will indicate whether scab development risk is high, medium or low to unlikely. "Producers need to consider the risk of scab within three days prior to flowering and 6 days after flowering and consider applying a triazole fungicide if the risk is moderate to high and the cultivar grown is susceptible," he said. The leaf rust prediction should be used only when leaf rust has been reported in the area since the rust fungus does not survive in South Dakota.

If used correctly, this system has potential to save growers money in one of two ways. "Either from unnecessary fungicide applications in case of low chances of significant disease development; or a timely rescue fungicide treatment that will protect yield which would have otherwise been lost to fungal diseases," said Shaukat Ali, SDSU Small Grains Plant Pathologist.

The weather information comes from the SDSU Climate and Weather Stations across the state that automatically links to the models. Both the weather variables and the forecasting website are provided by the SDSU Climate and Weather Center and are coordinated by Dennis Todey, SDSU Extension State Climatologist. The forecast system can be found by visiting, http://climate.sdstate.edu/smallgrains/.