The latest threat to our landscape focuses on crape myrtles, that summer-flowering small tree that’s becoming more and more popular as the climate warms.
An Asian-native bug known as crape myrtle bark scale has found its way north into Pennsylvania for the first time and threatens to stunt, disfigure, and possibly kill crape myrtles.
Crape myrtle bark scale was first reported in the U.S. in the Dallas, Texas, area in 2002, but was thought to be a warm-weather pest that wouldn’t spread beyond the southern states.
However, bark scales have been spreading “patchily” eastward and northward so that now the bug is operating in 18 states, including Delaware, Virginia, Maryland, New Jersey, and Washington, D.C.
Pennsylvania marks its northernmost spread.
Burkholder Plant Health Care, a Malvern plant-care company, first found the bark scale on crape myrtles in a yard in Chester County in 2022 and says it’s becoming more common there as well as in neighboring Delaware County.
The bugs are recognized by the small white bumps they build on crape myrtle stems and especially by the black sooty mold that’s a side effect of their “honeydew” (excreted waste). The bugs and/or their eggs live underneath the white bumps.
Burkholder says a tell-tale sign is that when you squish a few of the white bumps, it produces a “blob of dark pink goo.”
Infestations lead to stunted growth, branch dieback, less or no flowers, and in bad enough cases, death of the tree.
Sprays are most effective when applied shortly after eggs hatch in spring, typically from late May into early June.
What’s unclear is how well and how fast the bug will spread in Pennsylvania.
For one thing, crape myrtles aren’t as widely planted here as in the South, where the species is the No. 1 flowering landscape tree.
For another, it’s unknown which species will fare better in our colder winters — the bug or the tree. Both can tolerate mild winters with lows into the teens, but it’s possible that crape myrtles will be able to rebound from cold-winter diebacks to the ground while the bark scales won’t.
Besides crape myrtles, this bark scale has attacked Korean boxwoods, soybeans, apples, beautyberries, St. Johnswort, and spirea in infested regions.
More when-to-do-what tips are in George’s “Pennsylvania Month-by-Month Gardening” book.
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