There are some options to consider for managing apple scab. Captan, chlorothalonil, copper, maneb, mancozeb, sulfur, thiophanate-methyl are among the fungicides suggested. In the backyard orchard, home fruit tree sprays containing fungicides need to be applied at about the same times as for crabapples to provide protection from scab. Captan is suggested. Dormant oil sprays do not control scab.
Resistant varieties are the best way to manage scab, especially for ornamental crabapples.
There are many resistant cultivars available, so be sure to ask for them when selecting crabapples. Consider replacing extremely susceptible trees with resistant cultivars. Some apples also have resistance.