Acer tar spot

Symptoms

An outbreak of shiny black blotches, edged in a ring of yellow, disfigure acer leaves in early summer. This can lead them to fall prematurely.

Find it on: acers

Time to act: early summer

Problem categories

Overview

The fungus Rhytisma acerinum overwinters on fallen acer leaves, then infects the new spring foliage. The first signs are yellow leaf spots that turn into large shiny black blotches up to 1.5cm across. Severe cases can mean the leaves drop early, but the health of the tree won't suffer.

Solution

An outbreak of shiny black blotches, edged in a ring of yellow, disfigure acer leaves in early summer. This can lead them to fall prematurely.

Organic

Rake up and dispose of all fallen infected leaves.

Chemical

As a preventative measure use a recommended fungicide, containing either a Bordeaux mixture or copper, and spray before signs of infection and repeat at 10-15 day intervals.