It's Phytoplasmatic

Phytoplasma are specialized bacteria-like organisms that are obligate parasites of phloem tissue, and they can do strange things to plants.  Phytoplasma can cause leaf yellowing/variegation, twig distortion, witches brooms, etc.  They are spread by insects, like leaf hoppers, from infected plants to new hosts. 

In most instances infection by phytoplasma is not big deal, but in the case of a few diseases, namely; elm yellows, ash yellows, lilac witch’s broom, and grapevine yellows it can be deadly.  The best control method of phytoplasma is the removal, and offsite disposal of affected plant material.  Insecticide treatments to control the vectors may be helpful as well.

Diagnoses of phytoplasma can be difficult.  Viruses, bacteria, and fungal infections can mimic phytoplasma symptoms.  The picture below is a willow oak branch displaying some weird symptoms.  What’s causing it?  Phytoplasma?  Sure.