What's that strange orange dust covering roads and cars across the Tri-State?

Dust covering cars, sidewalks is identified
Posted at 8:43 AM, Jun 23, 2020
and last updated 2020-06-24 06:52:00-04

Pictures of an orange substance covering cars, sidewalks and pond surfaces came rolling in on Monday. And the overwhelming question was, "What is this?"


The orange dust is from the spores of a rust fungus sprouting on pear trees. Specifically, it looks like Callery pear trees were the most common host for this fungus. Other varieties of pear trees with fruits on the stems seem to have been infected with the fungus as well.

Joe Boggs with the OSU Extension office in Hamilton County put together a thorough article found HERE detailing the three conditions that had to be in place for this fungus to show up across the Tri-State.

"The source of the orange patina appears to be Gymnosporangium clavipes; the cedar-quince rust fungus," says Boggs.

The Southwest Ohio Air Quality Agency is also conducting a test today on their own samples gathered in Hamilton County.

GALLERY: No, it's not Cheeto dust

Outside of it being unsightly and a mess to clean up, the dust causes no harm and does not require treatment. Boggs says, "fruit infections cause no harm to the overall health of infected trees. Although the stem infections may cause minor tip dieback, the damage is usually inconsequential to tree health."

The orange substance can be seen on pear fruit. | Photo by Sandee Kurtz

So what happened? It was a perfect storm of just the right conditions. You have to have a juniper tree to start with the infected rust fungus, and then the wind has to carry it to a tree like the pear tree. It then grows on the fruit. A good rain then pulls the spores from the fungus and drops it to the ground.

"Not all host (plants) are susceptible to infection by this fungus. The cedar-quince rust fungus doesn't invade the stems to wreak havoc on the vascular system, nor does it infect the roots to produce root rots. It does infect the fruit, meaning that the greater the number of fruits, the greater the level of infection," detailed Boggs in his report.