How can irrigation influence disease pressure after fungicide applications?

• A. Irrigation has no effect on disease pressure after fungicide applications
• B. Dry irrigation and leaf dryness improve fungicide performance
• C. Excess irrigation or leaf wetness can promote diseases and reduce fungicide performance
• D. Only rainfall, not irrigation, affects disease pressure

Answer: (C)

Moisture on leaf surfaces is a key driver of many turf diseases and also affects how long a fungicide stays effective. When irrigation creates leaf wetness or high humidity after a spray, pathogens have a more favorable environment to infect and proliferate. At the same time, the water can physically wash off or dilute the protective fungicide residue, reducing its duration of action and overall effectiveness. So, excessive irrigation or persistent leaf wetness after application tends to increase disease pressure and lessen how well the fungicide works. The practical takeaway is to avoid overhead irrigation right after spraying, allow the leaves to dry, and (if irrigation is needed) plan with products that have good rainfast properties and appropriate timing to maintain protection.