Wheat Scab Risk Update

Posted: May 31, 2017

Wheat Scab Monitoring/Modeling efforts have recently estimated the risk to be low. However, if you have wheat flowering now, or set to flower in the next week, consider a spray for scab prevention.

Throughout PA we have been experiencing “Low” risk for the development of scab in wheat and barley…until now. Much of the southern part of PA as well as central areas are going to be increasing in risk level over the next several days. If you have wheat beginning to flower in the next few weeks, keep watching the model to see if risk is increasing: you will probably want to spray. 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 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 (see last week’s article for pics), 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. 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.

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. 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