Pest Susceptibility . Another important consideration when selecting trees and shrubs is their susceptibility to insects and diseases. Pests damage and occasionally kill susceptible plants. Fortunately, some pest problems can be avoided by careful selection of trees and shrubs. A common disease in the home landscape is apple scab on crabapples.
Apple scab causes heavy leaf drop on susceptible crabapple varieties.
Heavily defoliated trees survive, but are unattractive. Apple scab can be prevented by several applications of fungicides in the spring. Hopa', 'Radiant', 'Royalty', and 'Vanguard' are very susceptible to apple scab and are not recommended for the home landscape. Resistant varieties include 'Adams', 'Donald Wyman', 'Prairifire', 'Profusion', 'Snowdrift', 'Sugar Tyme', and others. Some insect problems can also be a avoided by careful plant selection.