Arbutus leaf spots

Arbutus are evergreen trees or shrubs, some of which also produce attractive red fruits. They can sometimes be affected by fungal leaf spot diseases, which may spoil their appearance and, in severe cases, lead to leaf loss and twig dieback.

Arbutus leaf spot

Quick facts

Common name Arbutus leaf spots
Scientific name Elsinoë mattiroloanum and Ruptoseptoria unedonis (syn. Septoria unedonis)
Plants affected Arbutus
Main symptoms Elsinoë: Purple spots and ring spots on leaves, purple lesions on twigs. Premature leaf fall. Twig dieback. Ruptoseptoria: Small, irregular, purple or brown leaf spots
Caused by Fungi
Timing Symptoms may be present year-round, but are likely to spread during summer

What are Arbutus leaf spots?

Leaf spots on arbutus are usually caused by one of two fungi. Elsinoë mattiroloanum is the more common and damaging, may be found on twigs as well as leaves, and can lead to leaf loss and twig dieback. Attacks by Ruptoseptoria unedonis are usually confined to the leaves.

Symptom

You may see the following symptoms:

Elsinoë mattiroloanum

  • Small purple leaf spots, often enlarging to form prominent purple ring spots (an outer purple ring with a green or yellow centre)
  • Purple, slightly raised, lesions on twigs
  • Leaves may turn yellow and fall prematurely
  • Twigs may die back

Ruptoseptoria unedonis

  • Small, brown to purple leaf spots, circular to more irregular in shape
  • Larger spots develop a whitish centre

Control

Non-chemical control

  • Remove and destroy affected leaves, or twigs with dieback, together with fallen leaves at the base of the plant
  • Encourage the production of vigorous, healthy growth by feeding, mulching to conserve moisture and watering of plants during periods of extended drought

Chemical control

There are no fungicides available to amateur gardeners with specific recommendations for use against leaf spots on arbutus. However, the fungicides tebuconazole (Bayer Fungus Fighter Concentrate), tebuconazole with trifloxystrobin (Bayer Fungus Fighter Plus), and triticonazole (Scotts Fungus Clear Ultra and Scotts Fungus Clear Ultra Gun) are labelled for the control of other diseases on ornamental plants, and could therefore be used legally on arbutus (at the owner’s risk) to try and control the leaf spotting.

There is no specific information available as to the efficacy of these products against arbutus leaf spots, however. It would be prudent to apply a small amount of the chosen fungicide first, at a solution suggested on the packet for other problems, to ensure that the product will not cause plant damage.

Inclusion of a fungicide product does not indicate a recommendation or endorsement by the RHS. It is a list of products currently available to the home gardener.

Download

Fungicides for gardeners (Adobe Acrobat pdf document outlining fungicides available to gardeners)

Links

Chemicals: using a sprayer
Chemicals: using safely and effectively
Chemicals: storing and disposing safely

Biology

The development of each of these diseases is likely to be favoured by wet weather conditions. Ruptoseptoria unedonis produces large numbers of microscopic spores from tiny fruiting bodies within the spots. The spores are splashed around by rain droplets and will infect if the leaf surface remains wet for an extended period. Little is known about the life-cycle of Elsinoë mattiroloanum.

As arbutus is an evergreen plant the fungi may be present on the leaves year-round, but could also potentially overwinter on fallen leaf debris or, in the case of Elsinoë, in lesions on the twigs.

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