Escallonia leaf spot is a fungal disease of Escallonia species, causing spotting on the leaves followed by defoliation. It was only first noticed a few 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

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.

Non-chemical control

• 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 by the disease may be too weak to respond to hard pruning
• Avoid other stresses on the plant – feed regularly and water during prolonged drought
• The disease appears to be specific to escallonia, so in the case of severely affected hedges consider replacement with a different plant

Fungicides

The RHS recommends that you don't use fungicides. Fungicides (including organic types) may reduce biodiversity, impact soil health and have wider adverse environmental effects. If you do intend to use a fungicide, please read the information given in the link and download below to ensure that use, storage and disposal of the product is done in a responsible and legally compliant manner.
  
The products listed in the ‘Fungicides for gardeners’ document below are legally available for use by home gardeners in the UK. This information is provided to avoid misuse of legal products and the use of unauthorised and untested products, which potentially has more serious consequences for the environment and wildlife than when products are used legally. Homemade products are not recommended as they are unregulated and usually untested.

There is no specific information available on the efficacy of any home garden fungicide against escallonia leaf spot.

Download

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

Link

Chemicals: storing and disposing safely

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.

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 relatively 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 produce new infections if the leaf surface stays wet for an extended period. The fungus probably persists on fallen leaf debris.