Pyracantha scab is a fungal disease of the blossoms, leaves and fruit of Pyracantha, resulting in leaf fall, loss of flowers and disfigured fruit.
What is pyracantha scab?
Pyracantha scab is an infection of the blossoms, leaves and fruit of Pyracantha by the fungus Venturia inaequalis f. sp. pyracanthae, resulting in flower loss, leaf fall and disfiguring black lesions on the fruit. The fungus was formerly known as Spilocaea pyracanthae but recent work demonstrated that the scab fungi affecting apple and pyracantha belong to the same species. Venturia inaequalis includes subpopulations which can only infect specific genera therefore the form that affects apple does not affect pyracantha and vice-versa. However, the scab fungus that affects Pyracantha also attacks Eriobotrya (loquat) and Mespilus (medlar) to a lesser extent.
You will see scab from spring until autumn.
You may see the following symptoms:
- On leaves Infection appears initially as dark spots on the leaf surface. Infected leaves soon fall and a severe attack can extensively defoliate the plant
- On flowers Infected flowers shrivel and do not form fruit
- On fruit Disfigured, blackened areas and cracking of the surface
- On stems Young stems may die back
The symptoms on stems are similar to fireblight, but fireblight infection on Pyracantha is more sudden and severe than scab.
- Hygiene is important for control, since the fungus survives winter on infected fallen leaves, infected fruits and pustules on infected stems. Rake up and burn or compost fallen leaves. Cut back infected parts to remove mummified fruits and stem infections. Note that rigorous cutting back will reduce flowering the following year
- Choose resistant plants. The Saphyr® range and ‘Golden Charmer’, ‘Shawnee’ and ‘Teton’ are all claimed to show some resistance to pyracantha scab
The only fungicide labelled to control scab on ornamentals is difenoconazole (Westland Plant Rescue Fungus Control). Products containing myclobutanil (Bayer Garden Systhane Fungus Fighter and other products), tebuconazole (Bayer Garden Multirose Concentrate 2) and triticonazole (Scotts Fungus Clear Ultra) are approved for use on ornamental plants for control of rusts and powdery mildews. They would probably also give useful control of pyracantha scab, although this is not claimed by the manufacturers. Liquid concentrate formulation of myclobutanil is approved for use by gardeners to control apple scab.
Fungicides for gardeners (Adobe Acrobat pdf document outlining fungicides available to gardeners)
The cause of scab on Pyracantha is the fungus Venturia inaequalis f. sp. pyracanthae. The fungus overwinters on fallen leaves and probably also on shrivelled fruit remaining on the plant and in pustules on the stems, then release spores to reinfect new growth in spring. The spores of Venturia inaequalis are dispersed mainly in water and to a limited extent by wind, so the disease is more severe under wet conditions. The spores of V. inaequalis are dispersed by wind.