Tomato Early Blight Control

Symptoms

Dark brown to black spots with characteristic concentric rings, looking like a target or bullseye, appear first on the older lower leaves. A yellow halo often surrounds the spots, and badly affected leaves turn yellow and drop off, defoliating the plant from the bottom upward. Dark sunken spots with rings can also form on stems near the soil line and at the stem end of fruits. The disease is favoured by warm humid weather with dew or light rain.

Damage

Early blight can cause yield losses of 30 to 60 percent in India, especially during humid weather, by destroying leaf area, weakening plants and exposing fruits to sunscald after defoliation. Fruit lesions make the produce unmarketable. Both tomato and potato are affected by the same fungus Alternaria solani. Because the fungus survives in crop debris and soil, infection usually starts on lower leaves and moves up if not checked early.

Organic & cultural control

Remove and destroy infected lower leaves and all crop debris after harvest to reduce the carryover of the fungus. Follow a three year crop rotation away from tomato, potato and brinjal. Use wider spacing and staking so the canopy dries quickly, and avoid overhead irrigation that wets the leaves. Spray of Trichoderma based bio fungicides and regular sprays of cow urine or panchgavya can help in early stages. Mulching keeps soil borne spores from splashing onto lower leaves.

Chemical control

As a protective spray use mancozeb 75 WP or chlorothalonil at the first sign of disease and repeat at 10 to 12 day intervals. If disease is advancing, systemic fungicides such as difenoconazole, azoxystrobin or a combination like azoxystrobin plus difenoconazole give better control. Alternate between contact and systemic products and between different fungicide groups to prevent resistance. Always follow the product label dose, observe the pre harvest interval and consult your KVK or agronomist before spraying.

Always follow the product label, the recommended pre-harvest interval, and your local KVK or agronomist. Pesticide approvals change, so verify before use.

Prevention

Use disease free certified seed and seedlings and treat seed before sowing. Practice crop rotation of at least two to three years away from solanaceous crops. Maintain good plant spacing, staking and weed control for air circulation, and irrigate at the base rather than over the leaves. Apply balanced fertiliser since weak, nitrogen starved plants are more susceptible, and remove and burn all infected debris at the end of the season.