Examine the upper two leaves or the flag leaf on 100 plants at 20-30 locations throughout the field. Scouting should be done every 4 days or so. Disease thresholds for fungicide application have not been determined in Iowa wheat, but other states have established thresholds. Fungicide application is warranted on susceptible varieties if the leaves you examine have an average of 1 percent of the leaf area diseased. You should consider rainfall forecasts as well as scouting information in your decision.
High rainfall favors more severe diseases.
Also, intervals between scouting can be longer if weather is very dry. The earliest effective fungicide application should occur at growth stage 8, or flag leaf emergence. In Iowa, Tilt can be sprayed only until flag leaf emergence. The window for spraying Tilt is short and early, and this limits its application substantially. Disease symptoms may not reach thresholds until after the window for Tilt application.