Apple Scab and its Management

Abstract

Apple scab caused by the fungus Venturia inaequalis (Cke.) Wint. is a destructive disease of apple. The pathogen is a facultative saprophyte that grows subcuticularly on the host. V. inaequalis must obtain nutrients through an active means. The fungus grows as a stroma of thick-walled cells between the cuticle and the outer wall of the host epidermis. Initial infections can lead to production of conidia on infected tissues within 9 to 17 days. The asexual spores can cause numerous secondary infections. Several waves of secondary infection can occur during a single growing season. Complete crop loss can result and severe infection can reduce blossom bud formation and crop potential for the following year, which may promote biennial bearing. Scab management is an essential component of orchard management in climates that are conducive to infection. Fungicides that are currently available for control of apple scab can be categorized as either protectant or eradicant in nature.