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Plantwise Factsheets for Farmers

Early blight on Tomato

Alternaria solani
Kenya

Recognize the problem

Tomato plants infected with early blight develop small dark brown to black spots on lower shaded leaves, stems and fruits. Leaves develop spots that are brown and leathery with faint concentric rings that look like a target. The spots later become uneven in shape. Spots on fruits often occur near the calyx end, where the fruit attaches to the plant.
In the seedbed the small plants wilt and eventually die. In older crops, stem death occurs while leaves fall off the crop and fruits drop early. The fruits are then exposed to sunburn.

Background

Early blight is a seed-borne disease that results in poor germination of seedlings. Disease development is most serious during warm wet conditions. It is caused by a fungus that also attacks old transplanted seedlings and plants that are stressed due to poor fertilization or attack by nematodes. The disease is also spread by wind, rain, running water, farm tools and also farm workers.

Management

Non-chemical control:
  • Use certified disease free seeds and tolerant varieties.
  • Practice crop rotation with non-host plants and plants that do not belong to the tomato family.
  • Avoid plant injury during transplanting.
  • Ensure a strong plant growth so that plants can escape attack of the fungus.
  • Plants should be staked and pruned correctly to allow good air flow and avoid disease spread.
  • Avoid planting tomatoes next to related crops like eggplant, pepper and potatoes.
  • Remove and destroy the old plants and weeds.
Chemical control:
  • Some of the effective chemicals available include Mancozeb, Azoxystrobin, copper oxychloride , Cymoxanil + Famoxadone, Dimethomorph + Mancozeb.

When using a pesticide, always wear protective clothing and follow the instructions on the product label, such as dosage, timing of application, and pre-harvest interval.

The recommendations in this factsheet are relevant to many countries where this pest or problem is present

Authors: This factsheet is based on information written for "The Tomato Farming Handbook", first published by KENGAP Horticulture, 2011.
Kengap Horticulture Ltd, P.O Box 12898-00400 Nairobi, Kenya
tel: +254 722 575544; +254 723 491549 email: books@kengap.co.ke; www.kengap.co.ke

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