Q: What is causing the growths on my bay tree leaves?
A: The red bay psyllid, Trioza magnoliae, was originally called the bay magnolia psyllid (Ashmead 1881) because the host plant from which it was originally described was believed to be the plant that is now known as sweet bay (Magnolia virginiana L.) which is in the family Magnoliaceae. However, there are no known verifiable records of this insect on plant species other than native species of Persea bay trees (Mead 1967) in the family Lauraceae. Most, but not all, species of psyllids are narrowly host specific (Hodkinson 1984), and R. magnoliae is not known to use even other species of Lauraceae besides P. borbonia (redbay tree) and P. palustris (swamp bay) as hosts. Therefore, it is referred to as the red bay psyllid.
Red bay psyllid galls are almost universally present on P. borbonia and P. palustris. In fact, they are so omnipresent that Nelson (1994) has suggested using the presence of the galls as an “identification clue” to these species of Persea. The galls cause absolutely no harm and no steps should be taken to cure the tree. Red bay psyllids are not believed to attack avocado, Persea americana Mill, which has also been threatened by the ambrosia beetle.
Persea borbonia, redbay, as well as other southeastern U.S. Lauraceae and some of the organisms dependent on this tree are now threatened by a lethal fungal species living in the exotic red bay ambrosia beetle, Xyleborus glabratus Eichhoff. It is this beetle which has destroyed thousands of acres of our native red bay species.
This information was provided through the Features Creatures article produced by the UF/IFAS Entomology & Nematology Department: http://entnemdept.ufl.edu/creatures/orn/trees/red_bay_psyllid.htm
For more information on the redbay tree check out the University of Florida publication by Dr. Ed Gilman: http://edis.ifas.ufl.edu/st436