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Small Grains Disease and Pest Update for 06/04/21

The scouts completed their weekly routes across Minnesota and found that grasshoppers in about half of the fields and aphids in over a third of all fields sampled.  Aphids appear not to have migrated north of Hwy 200 yet.  The incidence of aphids ranges from just a few percentage points of the stems having one or more aphids to fields that are near or above the threshold of 80% of the stems having one or more aphids. In general, incidences are higher in southern Minnesota than they are in northwest Minnesota.  In a few of the fields in the southern half of the state in which aphids were found, the scouts also found the first symptoms of BYDV.   

Overall, the scouts continue to find few if any fungal diseases.  One of the scouts found a trace of leaf rust in a winter wheat field in Olmsted county, while Dr. Jim Anderson confirmed stripe rust on the winter wheat variety trial on the St. Paul campus. The really hot and dry weather forecasted for the next few days will slow or halt the development of most fungal diseases.  

The FHB risk model was trending from moderate to high risk in SW Minnesota this past week.  The same hot and dry weather that slows or halts the development of other fungal diseases will also reduce the risk for FHB. 

This heatwave is now predicted to last through next week with little to no precipitation in the forecast and relatively low dew points across much of the southern half of the state. That makes the decision to apply a fungicide much harder as those conditions do not favor disease development.  Nevertheless, I suggest you consider applying a fungicide if your winter wheat reaches anthesis (Feekes 10.51) in the next few days and you find leaf rust or the tan spot/Spetoria complex of leaf spotting in the middle or higher up in of your canopy.  

I suggest that you hold off on applying a fungicide on your oats if it reaches Feekes 9 (flag leaf fully extended) in the next few days unless you can already find crown rust on the penultimate leaf or one leaf lower. 

More to come next week...

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