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Small Grain Disease Forecasting Model – Leaf Diseases (6/04/20)

Some of the earliest planted spring wheat crop is at (or near) jointing, whereas some of the winter wheat crop is at the flag leaf stage.

Some of the earliest planted spring wheat crop is at (or near) jointing, whereas some of the winter wheat crop is at the flag leaf stage. Now is a good time to check out leaf disease risk using the NDSU Small Grain Disease Forecasting Model (https://www.ag.ndsu.edu/cropdisease). As a reminder, this model is best used beginning at the jointing stage and after disease has been detected in the field.

Environmental parameters are used to determine disease risk for tan spot, Stagonospora/Septoria blotch and leaf rust. The tan spot model is driven by leaf wetness periods and growing degree days; blotch is driven by precipitation and relative humidity; and leaf rust is driven by leaf wetness periods and minimum nighttime temperatures. The leaf disease models use weather data from NDAWN locations positioned across ND, MT and MN. For example, in Figure 1 the weather data and disease risk (infection periods) are reported for Carrington for June 2. Notice that favorable conditions for tan spot development occurred between 5/23-5/27. Although this gives us a good estimate of favorable conditions for disease, remember that this model is best used after disease has been detected in a field. Tan spot is likely to be first identified in wheat fields with short rotations away from wheat and in reduced till operations. If you have detected tan spot at this point in the growing season, it is likely a fungicide has been tank-mixed with an herbicide to provide early-season control of tan spot. Continue to scout for the presence of tan spot on newer unprotected leaves (especially prior to the flag leaf stage) and keep track of the accumulation of infection periods (6 to 8 days of “Yes”) to determine if a fungicide application later on in the growing season is needed.

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Another important item to point out in Figure 1 is that the model indicated favorable conditions for leaf rust from 5/23-5/27. Leaf rust HAS NOT BEEN detected in North Dakota in 2020, so disregard infection period data for this disease until it is confirmed in the state. Spores of wheat rust pathogens are blown into North Dakota along southerly winds. To date, stripe rust has been reported in Nebraska, with most reports of leaf rust occurring in Oklahoma. If you find stripe rust or leaf rust in wheat, please send a photo to Andrew.j.friskop@ndsu.edu or @NDSUcerealpath.

 

Andrew Friskop

Extension Plant Pathology, Cereal Crops

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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