APPLE SCAB
Apple scab is one of the most common and most serious diseases that afflict apple trees. It usually appears in early to mid-spring and is more prevalent during rainy weather. The disease is caused by the fungus Venturia inqequalis, which overwinters in infected leaves left on the ground. The fungus spores are released in the spring during wet weather and are blown by the wind onto vulnerable, newly emerging leaves.
Apple scab first appears as small, olive-colored lesions on the undersides of the leaves. As the fungus spreads, the top sides of the leaves develop lesions, as well, that may become black or mottled with defined edges. Severely infected trees may become defoliated by mid-summer, making the tree vulnerable to other diseases. The fruit develop black or brown scabs or soft areas. The scabs may appear hardened and cracked, but don’t usually affect the inside of the fruit.
Several apple varieties, including Jonafree, Liberty, Enterprise, Pristine and Williams Pride are completely resistant to apple scab. Choose scab resistant varieties, especially if apple scab is a frequent problem in your area. Avoid Red Delicious, Cortland, McIntosh and Rome Beauty, which are all susceptible to the disease. Promptly rake up and remove leaves and debris in the fall and spray susceptible trees with fungicide in early spring, such as lime sulfur, sulfur or Captan.
Comments