Cause Wilsonomyces carpophilus, a fungus typically attacking the leaves of ornamental (flowering) cherries. Autumnalis (Prunus subhirtella 'autumnalis') is quite susceptible. The fungus overwinters on infected buds and twigs. Spores are primarily spread by water. The fungus can also attack stone fruits including peach, apricot, and fruiting cherries.
Symptoms Lesions are initially dark brown, reddish, or purplish spots and may be surrounded by a light green to yellowish halo. They are oval to round and expand into brown spots with light centers. The lesions are typically up to 0.25 inch in diameter. Centers of infected spots often die and drop out in warm weather, giving leaves the characteristic "shothole" appearance of the disease. Occasionally, twig cankers may be observed, especially on 'Autumnalis'.
- Avoid overhead watering, as leaves must be moist for infection to occur.
- Prune and destroy dead buds and cankered twigs if present.
- Rake and destroy infected leaves.
Chemical control Apply a fungicide at petal fall, shuck fall, and 2 weeks later. Rotate or tank-mix materials from different groups with different modes of action to prevent resistant strains from developing.
- Armada 50 WDG at 3 to 9 oz/100 gal water. Do not use a silicone-based surfactant. Not for nursery or greenhouse use. For non-bearing fruit trees only. Group 3 + 11 fungicide. 12-hr reentry.
- Bonide Fung-onil Multi-purpose Fungicide at 2.25 teaspoons/gal water. H
- Broadform at 5 to 7.6 fl oz/100 gal water. For non-bearing fruit trees only. Group 7 + 11 fungicide. 12-hr reentry.
- Daconil Weather Stik at 1.4 pints/100 gal water. Treated fruit must not be eaten. Group M5 fungicide. 12-hr reentry.
- Eagle 20 EW at 6 to 12 fl oz/100 gal water. Do not use treated fruit for food. Group 3 fungicide. 24-hr reentry.
- Myclobutanil 20 EW T&O at 6 to 12 fl oz/100 gal water plus spreading agent. May observe a PGR effect. Do not use treated fruit for food. Group 3 fungicide. 24-hr reentry.
- Protect DF at 1 to 2 lb/100 gal water plus 2 to 4 oz spreader-sticker. Do not use treated fruit for food. Group M3 fungicide. 24-hr reentry.
- Spectracide Immunox Multi-Purpose Fungicide Spray Concentrate for Gardens at 1 fl oz/gal water. Group 3 fungicide. H
Reference Pscheidt, J.W., and Byther, R.S. 2001. Prunus Diseases p 317-325 in Diseases of Woody Ornamentals and Trees in Nurseries, R. Jones., and M. Benson (ed.). St. Paul, MN: APS Press.