Scab Epidemic Risk Model
July 8, 2020
Plant Pathologist Commentary: Small Grains Disease Update 07/08/20
In my travels last week across northern Minnesota, I found little to no disease in the spring wheat trials or fields that I walked. I did find, however, plenty of standing water and drown outs. And, like in the southern part of the state, I did find the first signs of net blotch in barley.
On Monday I revisited the trials in LeCenter and in just 10 days since my last visit Bacterial Leaf Streak (BLS) had made its mark on the spring wheat trial. It was both amazing and disheartening to see how quickly BLS had torn through the canopy of some of the entries. Fortunately, there were also entries that to date had faired much better. These observations have been corroborated by reports from growers in southern Minnesota that have reported BLS to me.
The issue that is even more concerning than BLS is Fusarium Head Blight (FHB). The continued hot and humid weather across much of the state combined with the intermittent thunderstorms has meant and will mean that the risk of FHB infections has increased now to very high for varieties that are rated susceptible to very susceptible to the disease. The risk is now even moderate to high for varieties that are rated moderately susceptible or moderately resistant to FHB in many parts of the state.
The decision to apply a fungicide to suppress FHB is not a question of ‘if’ but a question of ‘when’ going forward. The immediate forecast continues to be hot and humid with scattered thunderstorms across much of the state. The only fields that are probably exempt are those that are in the pockets across the state that keep missing the thunderstorms and are actually drought-stressed.
The decision on whether to use tebuconazole or Prosaro/Caramba/Miravis Ace has not gotten any easier as the overall health and thus yield potential of the crop has been declining and likely will continue to decline with the continued hot weather and stress caused by the excess water. The later three fungicides each improve suppression of FHB by about 15% to 20% over tebuconazole.