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Cause The fungus Diplocarpon mespili (asexual: Entomosporium mespili), is most active during prolonged periods of cool, wet weather in the spring. Fungal spores overwinter on infected leaves or juvenile shoots. High humidity, cool weather, crowded plants, and splashing water from rain or overhead irrigation provide an ideal environment for disease spread. Host range is wide including Indian Hawthorn, photinia and quince.
Symptoms Leaf lesions arise as minute dots on newly developing leaves in spring. Lesions enlarge to form gray-brown, irregularly shaped spots with a red or brown border. Leaf spots mature as circular, brown lesions, 0.25 inch in diameter, with raised black fruiting bodies (acervuli) in the center of each spot. Leaf lesions can be few and scattered or can become so numerous that they coalesce to form large dead areas. Defoliation can be heavy with the onset of severe outbreaks of the disease. Infected areas on older leaves frequently have a gray-white cast due to the production of spore masses when leaves are wet. Infection of older leaves in late spring may also appear as white "ghost spots" on leaves when higher temperatures abort the progress of infection.
Cultural practices Careful inspection of container-grown plants in early spring helps identify early signs of leaf spot.
- Avoid overhead irrigation or apply such that plants are not wet for extended periods of time.
- Spacing of container plants helps prevent spread of disease to healthy plants.
- Take cuttings for propagation only from pathogen-free plants.
- Discard diseased cuttings and container stock. Remove and destroy diseased leaves and other debris from production beds.
- Rhaphiolepis x delacourii (hybrids) and the cultivars Clara, Eleanor Tabor, Indian Princess, Olivia, Ovata, and Snow White have shown resistance.
Chemical control Begin protective fungicide treatment before the casual fungus spreads and symptoms appear. Continue preventive applications at 10- to 14-day intervals until new shoot growth is finished. During heavy rain, shorten the spray interval to 7 to 10 days. Tank-mix and/or alternate products with different modes of action to prevent the build-up of resistant fungi. Limit the use of any one group during crop production.
- Avelyo at 3 to 5 fl oz/100 gal water. Group 3 fungicide. 12-hr reentry.
- Banner MAXX at 5 to 8 fl oz/100 gal water. Group 3 fungicide. 12-hr reentry.
- Broadform at 4 to 8 fl oz/100 gal water. Group 7 + 11 fungicide. 12-hr reentry.
- Concert at 22 to 35 fl oz/100 gal water. May cause injury to buds, blooms or tender new growth. Landscape use only. Group 3 + M5 fungicide. 12-hr reentry.
- Compass 50 WDG at 2 to 4 oz/100 gal water. Do not use organosilicate additives. Group 11 fungicide. 12-hr reentry.
- CuPRO 5000 at 3 to 5 lb/A but only up to 2 lb/A when new growth is present. Group M1 fungicide. 48-hr reentry.
- Daconil Weather Stik at 1.38 pints/100 gal water. Group M5 fungicide. 12-hr reentry.
- Eagle 20 EW at 6 to 12 fl oz/100 gal water. Group 3 fungicide. 24-hr reentry.
- Heritage at 1 to 4 oz/100 gal water plus a non-silicone-based wetter sticker. Group 11 fungicide. 4-hr reentry.
- Insignia SC at 6 to 12 fl oz/100 gal water. Do not use with organosilicate-based adjuvants. Use preventively only. Group 11 fungicide. 12-hr reentry.
- Junction at 2.5 to 5 lb/A. Spray solution pH should be above 6.5. Group M1 + M3 fungicide. 48-hr reentry.
- Monterey Liqui-Cop at 3 Tbsp/gal water. H
- Mural at 4 to 7 oz/100 gal water. Group 7 + 11 fungicide. 12-hr reentry.
- Nu-Cop 50 DF at 1 lb/100 gal water. Group M1 fungicide. 48-hr reentry.
- Pageant at 8 to 12 oz/100 gal water. Do not use with organosilicone-based adjuvants. Group 7 + 11 fungicide. 12-hr reentry.
- Phyton 27 at 1.5 to 3 oz/10 gal water. Group M1 fungicide. 48-hr reentry.
- Postiva at 10 to 28 fl oz/100 gal water. Group 3 + 7 fungicide. 12-hr reentry.
- Spectro 90 WDG at 1 to 2 lb/100 gal water. Group 1 + M5 fungicide. 12-hr reentry.
Reference Colbaugh, P., Hagan, A., Walker, J., and Barnes, L. 2001. Indian Hawthorn diseases. In: R.K. Jones, and D.M. Benson, 2001. Diseases of Woody Ornamentals and Trees in Nurseries. St. Paul, MN: APS Press.