The Ortho Home Gardener's Problem Solver



Dianthus: Alternaria Leaf Spot

Problem
Dark purple spots surrounded by yellow-green margins appear on the leaves and stems. Sunken, grayish brown dead areas develop in the center of the spots. Individual spots enlarge and merge to form blotches. Infected leaves turn yellow, blacken, then die. Lesions develop on stems, especially at the bases. Flowers may be spotted. The leaves at the tips of infected stems may become mottled, turn yellow, and wilt. The entire plant may eventually wilt and die.

Analysis
This plant disease is caused by a fungus (Alternaria dianthi) that infects carnations, pinks, and sweet william. Infection is most severe in wet, humid conditions. Spores are spread by wind and splashing water. Infection occurs when spores germinate on wet leaves, stems, or petals. The fungus survives as spores on plant debris.

Solution
Pick off and destroy infected plant parts and clean up and destroy plant debris. Spray with a fungicide containing chlorothalonil or captan according to label directions. Water in the morning so the foliage will have a chance to dry out. Try to avoid wetting foliage when watering.



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