Yellowing of Lilac
The yellowing of lilac is caused by mycoplasmalike organisms (MLO) and is widespread in the eastern United States. Lilacs can be infected by MLO, yet appear healthy.
Leaves are distorted, stunted and often chlorotic. Twigs are short, thin and often profuse. Leaf scorch and dieback sometimes develop. Vectors are unknown.
Mycoplasmalike organisms colonize in the sap (phloem), interrupting its flow and thus killing a growing point, which results in the dense growth of side shoots, usually low down on the plant. The late-flowering lilacs, particularly S. x josiflexa and S. x prestoniae are most susceptible. The shrub may look unhealthy, have twiggy growth and uncharacteristic out-of-season bloom or growth flushes and eventually die.
Pruning with sterilized tools is important. Dip or wipe the blades in rubbing alcohol, or a solution of 1 part household bleach to 10 parts water before you move to another plant. There is no known cure.
Diagnosed by the Monroe County Cooperative Extension.6/15/11