Lilac witches’-broom

Lilac witches’-broom (LWB) is a disease of lilacs caused by the Phytoplasma "Candidatus Phytoplasma fraxini". This phytoplasma was first identified as the causal agent of Ash Yellows and has since been attributed to both diseases.

Symptoms of the LWB phytoplasma include witches' brooms, shortened internodes on new growth, twig dieback, overall loss of vitality and premature death. Detection is primarily performed based on physiological symptoms in the host plant, although a new identification based on direct gene sequencing has been confirmed. There is no known cure for this disease so management strategies involving culling and proper disposal of infected specimens is encouraged.

The disease is believed to be spread by means of an insect vector, most likely of the order hemiptera. Certain cultivars of lilacs appear to be more susceptible, notably those of the Preston Lilac Series developed at the Central Experimental Farm in Ottawa Canada. Recent research performed there suggests heat treatment of scion material as an effective means of sterilization.