Pyracantha scab

Pyracantha scab is a fungal disease of the blossoms, leaves and fruit of Pyracantha, resulting in leaf fall, loss of flowers and disfigured fruit.

Pyracantha scab on berries

Quick facts

Common name Pyracantha scab
Scientific name Venturia inaequalis f. sp. pyracanthae
Plants affected Pyracantha, Eriobotyra (loquat) and Mespilus (medlar)
Main symptoms Dark spots on leaves, leaf fall, disfigured fruit
Caused by Fungus
Timing from spring through to autumn

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.

Symptoms

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.

Control

Non-chemical control

  • 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

Chemical control

The fungicides tebuconazole (Bayer Fungus Fighter Concentrate), tebuconazole with trifloxystrobin (Bayer Fungus Fighter Plus), and triticonazole (Scotts Fungus Clear Ultra and Scotts Fungus Clear Ultra Gun) are labelled for the control of a number of other diseases on ornamental plants, and may give some control of pyracantha scab, although this is not claimed by the manufacturers.

The following products contain a combination of both insecticide and fungicide, enabling the control of both insect pests and disease: myclobutanil containing cypermethrin (Bayer MultiRose 2, Doff Rose Shield, Vitax Rosegarde, Westland Rose Rescue); tebuconazole containing deltamethrin (Bayer Multirose Concentrate 2), and triticonazole containing acetamiprid (Scotts Roseclear Ultra and Scotts 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 pests are not a problem on the plants treated.

Download

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

Links

Chemicals: using a sprayer
Chemicals: using safely and effectively
Chemicals: storing and disposing safely

Biology

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.

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