Backyard black substance is natural, says CELS researcher

Heather Faubert

The black sticky stuff covering furniture and other backyard objects that has so many homeowners complaining in Coventry and elsewhere is just the result of a combination of natural occurrences, says a URI research associate.

Heather Faubert, who provides extension services to farmers, growers and landscapers throughout the state, said the substance is the result of a fungus mold growing on the excrement of tiny insects that suck juices out of trees.

It just so happens that starting last year and continuing into the spring of this year a scale insect, called the black banded lecanium, has undergone a population explosion, she says.

Live lecanium scale nymphs in early May

“I started seeing the scale problem in Charlestown last year and this year I started seeing them everywhere—in places like West Greenwich and South County, even Bristol,” says Faubert.

Dead adult lecanium scale on twigs and sooty mold on leaf

What happens, explains Faubert, is scales attach themselves to tree limbs and branches and start sucking out the plant’s juices. Oaks are prime targets but other trees are affected too, she adds.

“I was sitting under an oak tree on a gorgeous Mother’s Day last spring,” she recalls, “and it was raining on me.”

That “rain” was not water—rather it was “honeydew,” a nice word for the excrement that is produced by the sucking scale insects.

Dead lecanium scale nymphs on leaves

“The honeydew is like maple syrup—it’s sweet”—and then a fungus is attracted to it. The fungus results in “sooty mold,” a common problem on fruits such as apples in high humidity weather periods such as occur in August in these parts. Sooty mold is everywhere, notes Faubert and it lands on all sorts of horizontal objects such as outdoor furniture and cars.

The high population of scale insects, of course, resulted in a high number of eggs that turned into scale nymphs which also produced “honeydew.”

But things are looking up, adds Faubert. Last month, landscapers were bringing to her leaf samples with hundreds of white dots on them—“like polka-dots.”  The dots were actually dead scale insects.

“Historically we have seen insect populations build up and then come crashing down,” says Faubert who suspects the scale population bust has started.

Thus the case of the smudged backyard furniture may be resolved by the same thing that caused it—a cycle orchestrated by Mother Nature.