Early blight disease affects tomato and eggplant, but not pepper. It is caused by the fungus Alternaria solani. Potatoes are also susceptible to early blight.
Lesions can develop on leaves, fruit, and stems. The first foliar symptoms are brown necrotic spots on older leaves that enlarge over time. Younger leaves do not show visible symptoms. A yellow halo may develop around the lesions, and concentric rings develop when spores are produced. When there are numerous or large lesions,, the entire leaf may become yellow and fall off, exposing fruit underneath to potential sunscald. Severe infections result in reduced yield and lower quality of fruit. Seedlings can develop stem infections. Infected seedlings planted in the field either die as stem lesions enlarge or the plants may be stunted and unproductive. Fruit may also be infected. Lesions on green or ripe fruit develop near the calyx end and become leathery over time.
Optimum conditions for infection occur during warm (78-84⁰F), wet periods of rain, overhead irrigation, or heavy dew. The fungus survives in plant debris in the soil (main source for inoculum) and on seed. After landing on tomato plants, spores only require two hours to germinate and infect the plant. Lesions become evident two to three days later. Spores develop on lesions and are dispersed by wind.
- Use resistant varieties. ‘Mountain Supreme’, ‘Mountain Fresh’, ‘Plum Dandy’, ‘Mountain Magic’, and ‘Defiant PhR’ have resistance to the disease.
- Only use pathogen-free seed.
- Use Crop rotation. Rotate soil out of all solanaceous crops for at least two years.
- Provide good weed control and remove volunteer host plants (all solanaceous crops) this will help to reduce potential sources of inoculum.
- Keep plants vigorous through good soil fertility regimes.
- Use fungicides. See fungicide table below for a list of effective products for control of early blight.
How to Spot and Control Early Blight