Down Garden Services


Entomosporium Leaf Spot (Photinia Scab)

( Entomosporium maculatum )

picture of photinia leaves with entomosporium leaf spot
The left and centre images show the upper and lower surfaces of an affected Photinia leaf. The right image is of a fallen leaf which is showing the red pigmentation of juvenile leaves due to the natural senescence process.

This disease affects woody members of the Rosaceae Family but for gardeners it is most notable with the Photinias. Other hosts include pear trees, hawthorn, Pyracantha, Sorbus and quince.

picture of entomosporium maculatum spot
These early lesions were found on young beech tree leaves on a branch which overhung a standard Photinia 'Red Robin' bush that was heavily infected.

This Photinia Scab, as it may be called, attacks mainly fresh growth in the spring and autumn when the warm moist conditions it favours are present - temperatures above 14.5°C, 58°F. Small, bright red spots appear on the upper and lower surfaces of the leaf. These develop grey centres as the infection progresses and the spots may coalesce into larger maroon patches. Tiny black specks within the infected area are fruiting bodies which produce asexual spores (conidia) that are carried to other foliage by water splashes and the wind. Lesions can also appear on leaf petioles and young stems.
If the infection is severe the leaves may be cast as a defensive action by the plant, weakening it and in the worst case may kill it. Usually the badly affected mature leaves are dropped and the shrub looks bare. These fallen leaves can release spores to reinfect new growth.

The small black specks in this more mature lesion are the fruiting bodies.

The fallen leaves carry the disease over the winter and when the humid conditions return spores are released to be taken upwards in water splashes and rising air. Lower leaves are affected first, then the infection progresses further up the plant.

If the attack is spotted early the damaged leaves can be removed to prevent them releasing spores. They will not lose the blemishes and badly damaged leaves will be cast by the shrub anyway. Hygiene is important so fallen leaves must be cleared away and destroyed. Replacing the mulch around susceptible shrubs in spring should ensure any fragments of leaves or twigs are removed. Over fertilizing produces lots of soft growth which is more prone to attack. Leave plenty of space between plants to allow good air circulation which will dry the foliage more quickly after rainfall and reduce the risk of spread from splashes. Although the practice of pruning to encourage the attractive red shoots of Photinias is recommended this should be suspended if the Entomosporium Leaf Spot is around to reduce the amount of fresh growth which is more susceptible. A foliar spray of fungicide over the stems and leaves, especially to the lower sides, repeated every 14 days should treat the disease. This can be started when the conditions for infection are present if there has been a previous attack. An effective agent is Mancozeb (Dithane 945), which is a protectant that prevents the spores taking hold. Unfortunately it is no longer available to amateurs due to EU directives, but can be used in agriculture. Bordeaux mixture is another protectant and also unlicensed for sale, but the ingredients can be purchased for home manufacture. One of the limited number of fungicides available to the amateur gardener may have some effect if applied regularly along with the hygeine measures described above.

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