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Apple Scab - Venturia inaequalis  Clemson
University - USDA Cooperative Extension Slide Series, www.ipmimages.org
 HOSTS: Apple and crabapple. Pear is host to another
species of Venturia. DESCRIPTION:
Spots
begin as small olive green circles with velvety margins that enlarge
and darken to brown. Spots on fruit are dark and may be cracked.
Yellowing, browning, and death of leaves may result. Early drop may
occur. LIFE
CYCLE: Scab
fungi overwinter on fallen leaves. In the spring, overwintering spores
become wet and are forcibly discharged and disseminated by the wind.
Spores land on newly emerging leaf tissue and germinate in a film of
moisture. After germination the relative humidity must be 95% or
greater for infection to continue. Secondary infections occur
throughout the summer if weather is wet and warm. Optimum temperatures
for infection are 60 - 70°F. It takes 12 hours at a temperature of
53°F before infection occurs, while only 9 hours of leaf wetness
are required for infection at 65°F.CONTROLS:Biological: In some studies, compost tea was effective as a preventative, while in other studies, compost tea had no effect. Cultural: Keep water off of leaves and branches. Rake up and destroy infected leaves in the fall. Use resistant cultivars. See Table on Apples - Disease Resistant Cultivars. Chemical: Lime sulfur as buds start to break in the spring. Use oil-free lime sulfur to avoid bud injury. Sulfur when the weather is wet and warm (see life cycle). Must be reapplied when precipitation (or irrigation) is >1 inch since the last application. Daconil, if infection periods are high when leaves are first expanding - Check Pest Alert phone line: |
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