Look out for Tar Spots!


Tar spotKeep an eye out for Tar Spot in the coming weeks and learn more about local air quality. Late summer and autumn is the time of year that Tar Spot appears on the leaves of Sycamore and other trees.

OPAL scientists would like to know where and when you see the Tar Spot fungus.

Just complete the Tar Spot activity separately, or as part of the OPAL air survey.

What is Tar Spot?

Tar Spot (Rhytisma acerinum) is a fungus that affects the leaves of many tree species, but in particular Sycamore, Maple and Silver Maple. It shows up as dark black-brown spots each with a thin yellow border.

Tar Spot does not have any adverse effect on the tree’s long-term health.

Why are we interested in it?

Tar Spot is a known pollution indicator because it tends not to grow in areas with high amounts of sulphur dioxide. By recording Tar Spot on trees, you’ll help our scientists learn more about local air quality.

Take part

The Tar Spot activity is part of the OPAL Air Survey. To get started, simply download a copy of our tree guide and survey instructions: