What is X-spot, and how do I identify and manage the disease on apple trees?

The names X-spot, X-rot, and Nigrospora spot have been applied to a small, circular, depressed, necrotic spot typically on the calyx end of apple fruit in the mid-Atlantic region. Although uncommon, incidence of X-spot as high as 86% was reported on unprotected ‘Golden Delicious’ and ‘Rome Beauty’ fruit in 1950. Other susceptible cultivars include ‘Jonathan’, ‘Stayman Winesap’, and ‘York Imperial’. A fungus has been associated with X-spot lesions, but the typical lesion symptom has not been duplicated by controlled inoculation, and the disease cycle has not been resolved. Fungicides applied for summer diseases provide effective control of X-spot. Learn more in this article on X-spot.

Answer provided by Keith S. Yoder, Virginia Tech.