This year was a bad one for crabapple scab. Crabapple scab normally does not kill crabapples, but annual defoliation could weaken the trees, making them susceptible to other problems. Landscape managers can help improve the health of their flowering crabapples by doing the following:
1) While trees are dormant, rake up and destroy or chop up old, infected, fallen leaves where the fungus overwinters.
2) On mature landscape trees, thin out crabapple foliage by pruning selected branches to allow improved ventilation and sunlight penetration.
3) Professionals may want to consider application of fungicides in spring. To prevent primary infections, apply fungicides when the first green shoot tips are showing in early spring before flowers open and repeat 3 or 4 times at two-week intervals. Fungicide choices include protectants containing ingredients such as mancozeb or chlorothalonil. Eradicant fungicides containing thiophanate-methyl, or myclobutanil are also available.
4) Any new crabapple plantings should be done with disease-resistant cultivars.
Adapted from an article by John Hartman in the current edition of the Kentucky Pest News