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Fungicide for Scab Control: Late Application and Rain-fastness

Fungicide for Scab Control: Late Application and Rain-fastness
By Pierce Paul
Most of the wheat fields in the northern half of the state reached anthesis last week. The remaining fields will reach this critical growth stage during this week. According to the scab forecasting system (, the risk for Fusarium head blight (FHB; commonly referred to as head scab) has been moderate-to-high over the last 5-7 days on susceptible varieties planted in the northwest corner of the state. However, persistent rainfall, soggy fields, and difficulties scheduling an aerial application, prevented some fields from being sprayed to control scab and vomitoxin at the anthesis/flowering growth stage. But although anthesis is the recommended growth stage for head scab fungicide application, missing this window does not necessarily mean that you have lost the opportunity to use an effective fungicide to suppress head scab and vomitoxin.
If the risk for scab was high a few days ago when your field reached anthesis, but you were unable to apply a recommended fungicide, you can still make an application up to 6 days after anthesis and see good results in terms of scab and vomitoxin control. This is true for Prosaro, Caramba, and Miravis Ace. For instance, if your field of FHB susceptible wheat reached anthesis last Friday, May 31, when conditions were highly favorable for scab, but rain prevented you from applying a fungicide on Friday, you still have until the middle of this week to treat that field and achieve scab and vomitoxin control comparable to what you would expect had the field been treated on Friday. Applications made 4-6 days after anthesis are effective against vomitoxin and are particularly useful when the weather following anthesis is consistently favorable for scab. In fact, even if the scab risk had decreased from Friday to now, a late application would still be warranted, given that conditions were favorable for scab during the week leading up to anthesis.
Based on our research, both Prosaro and Caramba are very rainfast, and I suspect that Miravis Ace may be as well (based on the fact that propiconazole, one of the active ingredients in Miravis Ace, is very rainfast). Regardless of which of the three fungicides you choose to use to manage scab and vomitoxin, just make sure that they are applied at least an hour before it starts to rain, use a nonionic surfactant, and follow the labels.