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.
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.
You may see the following symptoms:
- 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
- Small, brown to purple leaf spots, circular to more irregular in shape
- Larger spots develop a whitish centre
The RHS believes that avoiding pests, diseases and weeds by good practice in cultivation methods, cultivar selection, garden hygiene and encouraging or introducing natural enemies, should be the first line of control. If chemical controls are used, they should be used only in a minimal and highly targeted manner.
- 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
The fungicide tebuconazole with trifloxystrobin (Provanto Fungus Fighter Plus, Toprose Fungus Control & Protect) has a recommendation for the control of leaf spots on ornamental plants. Additionally, the fungicides tebuconazole (Provanto Fungus Fighter Concentrate) and triticonazole (Fungus Clear Ultra) 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.
The following products contain a combination of both insecticide and fungicide, enabling the control of both invertebrates and disease: triticonazole containing acetamiprid (Roseclear Ultra, Roseclear Ultra Gun).When a proprietary product contains an insecticide as well as a fungicide it would be preferable to use an alternative product if invertebrate damage is not a problem on the plants treated.
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.
Fungicides for gardeners (Adobe Acrobat pdf document outlining fungicides available to gardeners)
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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