Apple Scab

Scientific Name: Venturia inequalis

Apple Scab is a fungal disease that infects apple trees causing lesions on the leaves and fruit. These lesions can also infect stems, resulting in dieback. Most apple cultivars are susceptible to scab and will require fungicidal sprays to prevent the disease. The disease rarely kills its host but causes unsightly defoliation. The pathogen overwinters primarily in infected leaves on the ground.

Attacks: Apples, crabapples, and Mountain ash

What you will see:

• Velvety brown to olive colored spots on leaves
  • Later, these spots turn black
• Heavily infected leaves may turn yellow and drop from the tree
• Fruit may also display lesions similar to leaves
  • Lesions become brown and corky
  • Infections cause fruit to mature unevenly and crack

Life cycle:

• In late fall and early spring, black pimples develop on infected leaves from the previous year
• Spores are released and blown by wind or splashed by rain to nearby trees
• The fungus may infect leaves, fruit, petioles, and blossoms
• Primary infections produce secondary spores which infect other leaves and fruit
• Secondary infections continue throughout the growing season during wet periods

Cultural Managements for Apple Scab

Cultural practices:

• Plant less susceptible cultivars
• Rake and dispose of fallen leaves to reduce spores
  • Do not compost infected leaves
• Improve air circulation through pruning
• Water at ground level only, avoid splashing on foliage