Q & A on foliar fungicides for wheat head scab
As it continues to rain, Ohio wheat producers, understandably, continue to ask questions about fungicides for Fusarium head blight, AKA Head Scab, management. Below is a list of questions asked by some of our producers and a set of straight-to-the-point answers based on years of scab research.
Q1: Which fungicide is the most effective against scab and vomitoxin?
A1: Based on data from 12 years of scab fungicide research, Prosaro, Caramba and Proline are the top three scab fungicides, providing very similar levels of control.
Q2: What about Folicur and other tebuconazole fungicides?
A2: Folicur and other tebuconazole do provide some level of scab and vomitoxin suppression, but our data show the Prosaro, Caramba and Proline provide between 10 and 15% greater control of scab, and between 20 to 25% greater control of vomitoxin than Folicur.
Q3: Will fungicide application at flowering for scab control also control foliar diseases?
A3: Yes. Both Prosaro and Caramba provide very good to excellent control of foliar diseases. In particular, application at flowering will provide very good control of Stagonospora, a disease that can develop late and affect both grain yield and quality.
Q4: Do I need to mix Prosaro or Caramba with another fungicide to control several other diseases such as powdery mildew, Septoria, and Stagonospora?
A4: No, mixing is not necessary; these fungicides control a wide range of foliar diseases on their own.
Q5: Will aerial application help to control scab?
A5: Yes, aerial application will suppress scab if done correctly. By correctly I mean if applied at flowering and using a volume of 5 gallons per acre.
Q6: Will application at heading control scab?
A6: Application at full head emergence (Feekes 10.5) will provide some level of scab suppression, but will not give you the best results.
Q7: What about applications after flowering?
A7: Applications made 2, 3, or even 4 days after flowering will also provide some level of scab suppression, but becomes increasingly less effective as you move further away from flowering.
Q8: What is the rainfast time” (“the time required between application and rain for the product to perform effectively”) for scab fungicides.
A8: There is very little or no university data on rainfast time for scab fungicides. However, based on the fact that these products are quickly taken up by the plant, the rainfast time could be considered the time it takes for the product to dry, which is anywhere between 15 minutes and 2 hours, depending on the weather conditions.
Q9: Will a fungicide application at flowering guarantee vomitoxin levels below 2 ppm?
A9: No! There are no guarantees that vomitoxin levels will be reduced below 2 ppm in every situation, especially if conditions are highly favorable for scab and the variety is highly susceptible. However, at this time, a fungicide application is your only option for trying to reduce vomitoxin to some acceptable level.
Q10: Should I prioritize treating fields will susceptible varieties or those with resistant varieties?
A10: Priority should be given to fields that are flowering, whether or not the variety is susceptible or resistant. No variety is completely resistant or immune to scab. A fungicide application to a resistant variety usually gives better results in terms of scab and vomitoxin reduction than a fungicide application to a susceptible variety.
Q11: Do I really have a 10-day window to apply a fungicide to control scab?
A11: No! You do not. You have at best a 5-day window, if you count a few day before and a few days after the beginning of flowering. The best time still remains at early flowering.