Early blight
Alternaria solani, Alternaria alternata
Symptoms
- Small, angular, strictly outlined spots with concentric circles
- Light brown to black lesions
- Lesions develop further at flowering into visual spots with sporulation
- Lesions tend not to grow across leaf veins
- Infected leaf becomes yellow and dries out
- Infection starts with the oldest lower leaves
- Plants under stress are more prone to infection
Infection and spread
- Survives as spores in the soil and on infected plant debris (mycelium)
- Alternative hosts include other Solanaceae eg. nightshades, tomato etc.
- Spread by wind and/or water splash
- Infection at temperatures between 10 - 35°C with alternating dry and wet periods
- Alternaria alternata is a weaker pathogen and generally a secondary infection
Possible confusion with
- Late blight (Phytophthora infestans)
- Micro-nutrient deficiency
- Ozone damage
- Difference between AS (Alternaria solani) and AA (Alternaria alternata) is difficult to determine in the field, a lab analysis is necessary
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