Root rot causes stems and roots to appear watersoaked and black. Do not compost diseased plants and do not replant china aster in the same spot. No chemical control is available. A rust disease causes bright yellowish orange spots on the undersides of leaves. This disease will be rare in most home gardens.
Gray mold causes blossom blight under cool moist conditions.
Remove and destroy infected plants and plant parts. Several leaf spots may attack China Aster. Aster yellows is transmitted by insects feeding on diseased plants then inoculating healthy plants when feeding on them. The plants rarely die but infected plants are a source of the disease organism. Control leafhoppers and remove infected plants as they are noticed.