See:
Carnation (Dianthus caryophyllus) - Alternaria Blight
Cause Septoria dianthi and Cladosporium echinulatum (sexual Mycosphaerella dianthi), fungi, have been found by the OSU Plant Clinic; Phyllosticta sp. has been reported in Washington. All are favored by wet conditions that keep leaves wet for extended periods of time. Cladosporium requires 15 to 20 hours of leaf wetness at 64°F.
Leaf spots due to the bacteria Pseudomonas sp. has also been found by the OSU Plant Clinic.
Symptoms Septoria produces roughly circular, light brown spots with a purplish brown border. Spots tend to be more numerous on lower leaves but are randomly scattered on the leaf. Spots continue to enlarge and eventually cause the leaf to die. Small, black, fruiting bodies (pycnidia) may be near the spots' centers. As the disease progresses, entire leaves and stems become necrotic. The whole plant develops a scorched appearance.
Leaf spots from Cladosporium have a light grayish center surrounded by a dark-reddish-to-black zone. This darker zone may extend lengthwise along the leaf. Leaves may be deformed or kinked if spots are near the margin. Spots can coalesce.
Cultural control
- Take cuttings from pathogen-free plants.
- Remove and destroy infected plant parts.
- Rotate plantings.
- Avoid overhead irrigation, or irrigate so that leaves are not wet for extended periods.
Chemical control Fungicides work best when applied during active plant growth but before symptoms develop and before wet weather is expected.
- Armada 50 WDG at 3 to 9 oz/100 gal water. Do not use a silicone-based surfactant. Not for nursery or greenhouse use. Group 3 + 11 fungicide. 12-hr reentry.
- 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.
- Compass 50 WDG at 2 to 4 oz/100 gal water. Do not use organosilicate additives. Group 11 fungicide. 12-hr reentry.
- Daconil Weather Stik at 1.38 pints/100 gal water. Avoid blooms. Group M5 fungicide. 12-hr reentry.
- Disarm 480 SC at 1 to 4 fl oz/100 gal water. Group 11 fungicide. 12-hr reentry.
- Fame SC at 1 to 4 fl oz/100 gal water. Group 11 fungicide. 12-hr reentry.
- Heritage at 1 to 8 oz/100 gal water plus a non-silicone-based wetter sticker. Group 11 fungicide. 4-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. 48-hr reentry general or 24-hr reentry for greenhouse.
- Ortho Rose & Flower Disease Control at 2 fl oz/gal water. Group 3 fungicide. H
- Pageant at 8 to 12 oz/100 gal water. Do not use with organosilicone-based adjuvants. Group 7 + 11 fungicide. 12-hr reentry.
- Spectracide Immunox Multi-Purpose Fungicide Spray Concentrate for Gardens at 1 fl oz/gal water. Group 3 fungicide. H
- Tourney EZ at 1 to 4 oz/100 gal water. Group 3 fungicide. 12-hr reentry.
- Trinity at 4 to 12 fl oz/100 gal water. Group 3 fungicide. 12-hr reentry.
Reference David, J.C. 1988. Cladosporium echinulatum. CMI descriptions of pathogenic fungi and bacteria, No. 957. Mycopathologia 103:117-118.