By Pierce Paul, Ohio State University Extension plant pathologist
What should I spray for scab and vomitoxin control? With the addition of Miravis Ace (a new DMI + SDHI premix) to the list of fungicides recommended for the control of Fusarium head blight (head scab) and vomitoxin in wheat and barley, questions are being asked as to whether it is any better than Prosaro and Caramba. In 2018, we compared the three fungicides on scab susceptible varieties across 12 environments and found that in terms of efficacy against head scab and vomitoxin, Prosaro, Caramba, and Miravis Ace were very comparable. Disease severity, vomitoxin contamination, and fungicide efficacy varied among locations, but on average, all three fungicides reducing scab by about 55-60% and vomitoxin by approximately 50-55%.
When should these fungicides be sprayed for scab control? Another commonly asked question about Miravis Ace pertains to its efficacy when applied at early heading (Feekes 10.3). Until we have sufficient data to suggest otherwise, our recommendation would be to apply these fungicides at or a few days after heading in barley or at or a few days after flowering in wheat for best results in terms of scab and vomitoxin control. We have more than a decade of data clearly showing that Prosaro and Caramba are considerably less effective, particularly again vomitoxin, when applied early (5 days before anthesis in wheat or 5 days before heading in barley) than when applied at the recommended growth stages. Based on a much smaller set of data, similar trends were observed with Miravis Ace in 2018; efficacy in terms of vomitoxin control was much more variable when the fungicide was applied at Feekes 10.3 than at Feekes 10.5.1 in wheat or 10.5 in barley.
What about other diseases? Again, based on a limited number of trials in which the three fungicides were compared side-by-side, Miravis Ace, Prosaro, and Caramba seem to be very comparable in terms of their efficacy against powdery mildew, rust, Septoria, and Stagonospora. For control of late-season diseases such as the rusts and Stagonospora glume blotch, and single application of Miravis Ace at anthesis performed just as well as a single application of Prosaro or Caramba at the same growth stage. However, for early-season diseases such as powdery mildew and Septoria, applications made between Feekes 8 (full flag leaf emergence) and Feekes 10 (boot) were more effective than applications made at or after anthesis.