Small Grain Disease Update – April 1, 2016

Nathan Kleczewski, Extension Specialist – Plant Pathology; nkleczew@udel.edu

Since my last article, the temperatures have been fairly cool and very windy, which has not been favorable for disease development. We are seeing low levels of spot/net blotch in barley and some minor powdery mildew in some wheat fields and varieties. There are also a few-virus-like symptoms out there, but nothing widespread at this point. Typically we see symptoms of the soil borne viruses at this point in time, when weather is cool. When we warm up and put on the second shot of N, symptoms disappear. If you do see some virus-like symptoms in small grains call your county Extension Agent or myself and we’d be glad to help you get them tested for virus.

As I mentioned on March 4, only consider a fungicide treatment with your 2nd nitrogen application if you see powdery mildew in your fields at this time. There are striking differences in varietal resistance, so you can save the fungicide cost, potential environmental impacts, and potential fungicide resistance development by scouting your fields before you make that second application of nitrogen. Applications at FGS 4-5, with the first shot of nitrogen, are not going to provide you much benefit. The plant is not actively growing, it is cold, and the fungus is likely still dormant. Dormant fungi are not impacted much by fungicides, particularly the DMI-group 3 class. The best chance to see an early application pay off, is when applied with the second shot of nitrogen in fields where powdery mildew is already present. I do worry that if we continue to apply propiconazole or other DMI (group 3) fungicides to fields at cut rates and without need that we will soon see fungicide resistance develop to these fungicides. We do not need that in addition to all of the other issues we are currently facing. As usual, the best thing you can do is scout your fields to ensure that you are making applications when they are needed and at the appropriate time. A good disease resistance package goes a long way in wheat and barley.

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