Wheat Scab Risk Update

Posted: May 24, 2017

Yes, it’s wet, but head scab risk is still low. Why is that?
Figure 1. Early Flowering (note yellow pollen filled anthers)

Figure 1. Early Flowering (note yellow pollen filled anthers)

Throughout PA we are experiencing “Low” risk for the development of scab in wheat and barley. While the humidity levels have been high, the temperatures have not been high enough for the fungus to make spores. When it has been dry or cool for about the two weeks prior to flowering, the fungus is not able to make the spores that get into your wheat and cause infection. The FHB Risk Assessment Tool takes what we know about the biology of the fungus along with the current and past weather and uses that to predict how much of the fungus is around to cause disease. If you have wheat beginning to flower in the next few weeks, keep watching the model to see if risk is increasing. This forecasting site is an online model that helps us predict infection risk levels everywhere in the state. It has been improved over the last few years to include some new features and better accuracy. Visit it at your convenience, or sign up to have my updates e-mailed or texted directly to you.

Use your judgement based on your experience and your local conditions. Be prepared to spray a fungicide on fields that are at medium to high risk at flowering, especially if you are growing a susceptible variety. Remember, sprays applied PRIOR to flowering will NOT provide significant suppression of scab or toxin production, however, a spray up to a week after the beginning of flowering can offer good disease and toxin reduction. Caramba or Prosaro are effective on scab and give control of most leaf diseases and glume blotch. They do not need to be tank mixed with another product to control these diseases. If either of these products is unavailable, Proline and Folicur (which together provide the same chemicals as Prosaro) may be tank mixed at a rate of 3 + 3 fl oz/A. 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.

Once wheat begins flowering (Figure 1. Early Flowering), there is about a 5-6 day window to apply a fungicide. If you feel like you have missed that early flowering target, you can still apply later and get some disease reduction (Figure 2. Late Flowering). The labels state the last stage of application is mid-flower and there is a 30-day 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.

Wheat scab

Figure 2. Late Flowering (Empty white anthers)

At this point in the season, the only way to reduce the scab problem is to spray. In general, do not rely solely on fungicides, as they will provide at most a 50–60% reduction in scab severity and vomitoxin. Choose resistant wheat varieties, and time sprays properly to achieve greater control.

Contact Information

Alyssa Collins
  • Research Associate, Southeast Ag Research and Extension Center
Phone: 717-653-4728