Current status of sanitation and new roles in apple scab management

Abstract: Sanitation is recommended in all apple scab IPM programs, but growers considersanitation optional rather than indispensable. A review of studies that investigated theeffectiveness of urea and shredding the leaf litter to reduce ascospores, the major source ofprimary inoculum causing apple scab, has led to a prediction that, in routine practice, applying5% urea to trees after harvest and shredding the leaf litter in spring will reduce the ascosporedose approximately 70%. These combined practices are required in a New Hampshire (NH)Sanitation Program that significantly reduces fungicide in a low-scab-risk orchard by leavingearly-season infection periods unprotected. Sanitation has two clearly-defined roles that make itindispensible to the program’s success: sanitation (1) compensates for errors in an autumn foliarscab assessment that identifies an orchard’s level of scab-risk next season and (2) reduces thepotential for an unacceptable buildup of scabbed fruit in a low scab-risk orchard that leaves earlyseasoninfection periods unprotected. For decades, chemicals, machinery, and biological agentshave been screened to determine their effectiveness in reducing the ascospore dose. Screening toidentify sanitation practices that will reduce the ascospore dose > 90%, in routine practice, shouldcontinue because this will optimize the roles of sanitation in scab management, but the NHsanitation program demonstrates that the goal of sanitation, i.e. integrating sanitation into a scabmanagement program to reduce the fungicide dose, can be achieved with the efficiency ofsanitation practices available now.