Codling moths lay eggs on developing fruits shortly after petals fall in spring. Eggs hatch in a few days, and young larvae tunnel into fruits where they feed and mature, destroying the fruit in the process. The best remedy is spraying Bacillus thuringiensis kurstaki in the evening 15 days after petals begin to fall. Repeat five days later. The spray is toxic to caterpillars only.
Apple scab is a fungal disease that causes black splotches on leaves and fruit.
It is most common and severe in the eastern U.S. where summer rainfall is common, but it occurs in all apple-growing regions. The first line of defense is to plant scab-resistant varieties such as 'Enterprise', 'Freedom', 'Gold Rush', 'Jonafree', 'Liberty', 'Macfree', 'McShay', 'Nova Easygro', 'Prima', 'Priscilla', 'Pristine', 'Redfree', 'Sir Prize', and 'William's Pride'. If you've inherited a disease-prone variety, sulfur sprays can control the disease. Use liquid sulfur, spraying it over the tree once flower buds show pink. Repeat 10 days later.