Apple Scab Management Options for High-Inoculum Orchards

Apple scab emerged as an expensive problem in apple orchards throughout the Northeastern United States in 2009. Experienced growers who had managed scab effectively for many years found themselves spray ing throughout summer to control scab that kept appearing on new leaves. Th e effort required to protect fruit from scab during summer increased production costs and represents a “loss” to apple scab even where no scab was present on fruit at harvest. Given the prevalence of scabby leaves in orchards at the end of 2009, the average New York apple orchard may be carrying more over-wintering scab inoculum in spring of 2010 than at any other time in the past 40 years. If spring weather favors scab development, these high inoculum levels could contribute to massive scab control failures and signifi cant crop loss in the coming year. As always, there are big discrepancies among orchards even within rather small geographic areas. Where no scab was present on leaves last season, spray programs used in previous years can probably be used again in 2010. However, where scab was a problem in 2009, control strategies may need to be adjusted for the 2010 season.