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High Fusarium Head Scab Infection Risk

High Fusarium Head Scab Infection Risk
By Alyssa Collins
Wheat across southern PA is heading now, while risk for scab infection is increasing. Be sure to keep an eye on the FHB Risk Assessment Tool as it will become critical for those farmers who are trying to make the decision to spray small grains or not. This forecasting site is an online model that helps us predict infection risk levels everywhere in the state. It works best in the Mozilla Firefox browser and updates each day around 10 a.m. Visit it at your convenience or sign up to have updates emailed or texted directly to you. I will add commentary about disease risk in our area to give some human perspective, and you can have this commentary sent to your e-mail or phone by signing up.
Sprays prior to heading do not suppress scab, but one labeled fungicide, Miravis Ace may be applied at 50% heading. The best control with all fungicides will result from spraying at the first sign of anthers. Caramba and Prosaro (Group 3) or Miravis Ace (Group 3 + 7), give good control of scab as well as most leaf and head diseases. All three products provide similar disease suppression. They do not need to be tank mixed with another product to control these diseases. Spray nozzles should be angled at 30° down from horizontal, toward the grain heads, using forward- and backward-mounted nozzles or nozzles with a two-directional spray, such as Twinjet nozzles. These sprays become rainfast quickly, and so an application followed by rain should not be cause for alarm.
Once your crop begins heading, there is approximately a 5 to 6 day window to apply a fungicide. The labels state that the last stage of application is mid-flower and there is a 30 days to harvest restriction. Do not use any of the strobilurins (Quadris, Headline), or strobilurin/triazole (Twinline, Quilt, Stratego) combination products at flowering or later. There is evidence that they may cause an increase in mycotoxin production.
At this point in the season, the only way to reduce the scab problem is to spray. But in general, do not rely solely on fungicides, as they will provide at most a 50-60% reduction in scab severity and vomitoxin. The best long-term management strategy starts with selecting resistant varieties, and then timing sprays properly to achieve greater control.