It is a common fungal disease in cabbage caused by Alternaria brassicicola. And the chances for the infection is high during extended cool, rainy weather. It also infects the other members of brassicase family such as broccoli, cauliflower and Brussels sprouts, Turnip, Kale, Chineses Cabbage.
The pathogen can survive for many years on the infected plant debris.
Identification of Alternaria leaf spot.
The fungus spread from one plant to another by the help of wind, water splash, people, and equipment. The disease is
favored by moist and warm weather (75-82 °F). Under those conditions, spores can be produced within a week, and start a new disease cycle. Several disease cycles can be completed in a season under favorable conditions.
Flowering stage, Fruiting stage, Post-harvest, Pre-emergence, Seedling stage, Vegetative growing stage.
Alternaria leaf spot Damage.
Small dark spots on leaves which turn brown to grey; lesions may be round or angular and may possess a yellow-black margin; lesions may form concentric rings, become brittle and crack in the center; dark brown elongated lesions may develop on stems and petioles. You can also see the lesion on a flower, flower pedicels and seed pods.
Controls & Prevention.
1. Use certified seeds.
2. Crop rotation with Non- host plants.
3. Clean the infected plant debris.
4. Avoid excess irrigation during head development.
5. Weed control at regular intervals.
6. Maintain distance between plants.