Andrew Friskop, Extension Plant Pathologist at NDSU, shared my concern that the risk models were underestimating the risk of FHB last week. Since the weekend the models have started to trend towards moderate to high risk across much of North Dakota and Northwest Minnesota. Below are his thoughts and my two cents about the current risk situation, a summary of the efficacy of the different fungicides, and some thoughts about if and when to spray fungicides in lodged grain.Risk Models:
This past weekend’s weather for most of the state presented conditions of high humidity, rain, and prolonged dews. These three factors greatly contribute to scab risk and now an elevated scab risk exists for small grains (click here to see the most recent maps). According to the NDSU Small Grain Disease Forecasting Model, the greatest scab risk exists for spring wheat varieties that are rated as very susceptible and susceptible to Fusarium head blight varieties. This includes varieties like AP Murdock, SY Longmire, WB 9479, and WB9590. However, there is still a moderate risk for the spring wheat varieties that are rated as moderately susceptible and moderately resistant in parts of North Dakota (and Minnesota).
When looking at the immediate forecast, high humidity levels will be sporadic amongst the days, yet prolonged morning dews are still likely to occur at least a couple times this week. Given this past weekend’s weather and the forecast, scab risk will likely remain elevated for this week.Fungicide Efficacy:
There are several labeled fungicides that provide *good* scab suppression of scab. These include Caramba®, Proline®, Prosaro®, Prosaro Pro®, Miravis Ace®, and Sphaerex®. Fungicides with the sole active ingredient of tebuconazole are rated as *fair*. The active ingredient propiconazole has *poor* efficacy on scab. To put this in terms of percentage reduction of scab and deoxynivalenol (DON/VOM), *good* fungicides provide about 45-60% suppression, *fair* fungicides may only offer 20-25% suppression, and *poor* fungicides provide only about 10% suppression. Understand that tank mixing fungicides does not mean that the efficacy of the tank mix is the sum of both products. In other words, adding tebuconazole to Caramba does not increase the level suppression of scab to 80% or more. Finally, remember that the premixes that do contain tebuconazole are to create a product that provides good to excellent control of other fungal pathogens, including tan spot an d leaf rust.
--Jochum Wiersma, Small Grains Specialist, University of Minnesota