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Small Grains Disease and Pest Update 06/22/23

It's trying to rain at the moment in Crookston. So far it has only really wetted the sidewalk. The forecast remains, however, hopeful for rain throughout the region.  Does that mean that a 5-alarm fire for leaf diseases and or Fusarium head blight is imminent? Just like a single robin doesn't make spring, a single weather system does not make for widespread and economic levels of leaf diseases or Fusarium head blight. The disease forecasting that is part of the NDAWN system in the tri-state area and the National Fusarium Risk Tool are weather-based models that try to quantify how good the conditions are for individual diseases to start infections.  

Two more factors make the disease triangle, namely the presence of a host that is susceptible to a disease and the presence of the disease spores to cause infections.  It is especially the latter that might be missing at this point, given the very low incidence of all diseases last year, the very dry conditions throughout last year, and the continued dry weather this spring. The leaf diseases like tan spot, Septoria, leaf, and stripe rust will need two or three generations of cycles before they would be able to reach economically damaging levels, something that for the earliest heading wheat seems unlikely.  Likewise, I expect the risk models for FHB to remain low even if we have 4 days with cooler, wetter weather.

I am, therefore, at this point hesitant to recommend the application of a fungicide at Feekes 10.51/the beginning of anthesis.  Only if you are in an area that has received more rainfall than the rest of us, would I contemplate a fungicide application.  Do, however, scout for any insect problems (aphids, armyworms, grasshoppers, or cereal leaf beetle) to determine whether you are at or near the threshold before deciding not to spray a fungicide. 

Fungicides will not prevent Bacterial Leaf Streak (BLS). Below is a picture taken by Amelia Landsverk, one of the scouts funded by your wheat check-off dollars.  It shows the beginnings of a BLS infection in wheat. Note the long, elongated lesion in between the veins and the water-soaked appearance of the green leaf tissue on the edges of the lesion.

Early infection of Bacterial Leaf Streak (BLS) in wheat caused by
Xanthomonas translucent (Photo by Amelia Landsverk).

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