Escallonia is a reliable, hardy, flowering shrub suitable for use as specimen plants or as hedging. Until recently it has been free from foliar disease problems but a new fungal disease causing leaf spots and defoliation is causing concern.
What is Escallonia leaf spot?
Escallonia leaf spot is a fungal disease of Escallonia, causing spotting on the leaves followed by defoliation. It was first noticed three or four years ago but has since spread rapidly. Severely affected plants can be reduced to bare branches.
You may see the following symptoms:
- Purple to black leaf spots, circular or more irregular in shape
- The spots often develop a greyish-white centre
- Fungal fruiting bodies may just be visible within the leaf spot. These are most obvious as tiny black dots in the white centre of the spot
- Several spots may be present on a single leaf
- Affected leaves turn yellow (starting around the spots) and fall from the plant
- Defoliated plants usually produce new leaves, but these often develop further symptoms
- Repeated leaf loss is likely to severely affect plant vigour
- Dispose of affected leaves and any that have already fallen as a result of the disease. Note that, as an evergreen plant, escallonia will shed old leaves naturally throughout the year, but the leaf spot can affect leaves of any age
- Affected plants could be cut back hard to stimulate new growth. Fungicide application may be necessary to prevent re-infection (see below). Be aware, however, that plants that have suffered repeated defoliation may be too weak to respond to hard pruning
- Avoid other stresses on the plant – feed regularly and water during prolonged drought
- The disease appear to be specific to escallonia, so in the case of severely affected hedges consider replacement with a different plant
There are no fungicides available to amateur gardeners with specific recommendations for use escallonia leaf spot. However, the fungicides difenoconazole (Westland Plant Rescue Fungus Control), myclobutanil (Bayer Garden Systhane Fungus Fighter), tebuconazole (Bayer Garden Multirose 2) and triticonazole (Scotts Fungus Clear Ultra) are labelled for the control of some other diseases on ornamental plants and could therefore be used legally on Escallonia (at the owner’s risk) to try and control leaf spot.
There is no specific information available as to the efficacy of these products against the leaf spot, however. It is likely that repeated sprays will be required where the disease is present, particularly during unsettled weather. Success is more likely if the plant is cut back hard to remove affected material, and then sprays applied to protect the new growth. 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.
Fungicides for gardeners (Adobe Acrobat pdf document outlining fungicides available to gardeners)
Examination of samples received by the RHS has shown that two different fungi may be associated with the leaf spots (although they are never found together in the same spot). The first, and by far the most common, is a Septoria species. This produces the tiny black fruiting bodies described above – under wet conditions colourless tendrils of spores ‘ooze’ from these fruiting bodies. Occasionally, a Cercospora species can be found instead – this produces ‘tufts’ of spores rather than black fruiting bodies. Work is currently being undertaken by the RHS Plant Pathology department in collaboration with Royal Botanic Gardens Kew and the University of Reading into the precise identification of the species of Septoria and Cercospora involved.
Many fungi produce asexual and sexual types of spore at different stages of their life-cycle. Unfortunately, the fungus is often given a completely different scientific name depending on what type of spore it is producing, which can be very confusing! Both Septoria and Cercospora species produce asexual spores. In each case, if the fungus were to produce sexual spores it would be known as a Mycosphaerella species. Although these sexual spores have yet to be found on affected leaves, the disease is therefore usually referred to as Mycosphaerella leaf spot.
As this is a new problem the precise conditions for spread of the disease are unknown, but it is certainly favoured by wet weather conditions. Spores are likely to be splashed around by rain droplets, germinating to set up new infections if the leaf surface stays wet for an extended period. The fungus probably persists on fallen leaf debris.
Common nameEscallonia leaf spot
Scientific name Mycosphaerella species
Plants affected Escallonia
Main symptoms Purple to black spots, often with grey-white centres. Leaf yellowing and defoliation
Caused by Fungus
Timing Summer, particularly in wet conditions (although as an evergreen plant leaf spots may be visible at other times of year)