The Village of Mount Prospect received reports from residents observing a black, soot-like residue on the exterior of their homes and vehicles over the past several weeks. The Village published a press release on October 9, 2025, informing the community that staff were monitoring the situation and shared that similar reports were being made in surrounding communities.
Public Works Department - Forestry Division recently inspected the reported areas and trees and believe the cause of the black soot and stickiness to be Cottony Maple Scale, a common insect pest.
According to The Morton Arboretum, the Cottony Maple Scale (Pulniaria innumerabilis) is usually hosted by silver maples, boxelders, and other maple, apple, and oak trees. The insect is native to North America.
Morton Arboretum states that scale insects look different than other insects and can be very small (less than 1/32 inch). When the insect is mature, you can see them with your eye.
Cottony Maple Scale is a soft scale insect. The insect covers themselves with waxy secretions. According to the University of Maryland, the sugary waste excretion produced by the insects is called Honeydew. The insects need to ingest a lot of sap as part of their digestive process. The sugary water/stickiness is an undigested product that passes through the insect which is then excreted as waste and then it is Honeydew. The honeydew drops onto surfaces.
The honeydew build up can be rapid and substantial before it is detected by people. Leaves or other surfaces layered in Honeydew look shinier and will be sticky.
The black sooty material is likely sooty mold according to the Village of Mount Prospect Forestry Division. As noted by the University of Maryland, sooty mold can grow on leaves coated with honeydew and stress the trees interfering with photosynthesis causing tree leaves to fall sooner. The sooty mold also can grow on inanimate surfaces coated in
honeydew, such as vehicles, houses, roofs, bark, outdoor furniture, walls, cars, sidewalks and garbage cans. In can reappear in days or even hours.
In most years the soft scale insect is considered a minor insect. Every few years the population increases dramatically and does more damage. Natural predators then reduce the population significantly. As noted by Village arborists, this season is some of the worst Cottony Maple Scale and honeydew they have seen in 20 years. The mild winters contributed to the soft scale insect population exploding, making the honeydew and sooty mold more noticeable in the community.
To clean off the sooty mold and honeydew off of surfaces, we suggest checking with the EPA at https://www.epa.gov/saferchoice to review cleaning products that are a safer option. Also, please check with the manufacturer of the product that you are cleaning for special cleaning instructions, possible brushes to use, or hand washing recommendations. There are many options depending upon the surface and results may vary.
The Village appreciates the community feedback about the black soot noticed in the community. Staff will continue to share any concerns with our local, county and state agencies as necessary.
If you have any questions about Cottony Maple Scale or sooty mold, please contact a licensed arborist, an arboretum, or nursery to assist with landscape questions.
