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Factsheet for Farmers
29 January 2015

Late Blight of Tomatoes: Phytophthora infestans

Recognize the problem

Late blight is the most serious disease of tomato. It is present mostly in hilly areas. Water soaked, oily, dark green spots are first seen on young leaves at the top of the plant and later, leaves shrivel and die. Spots also occur on stem and fruit and will turn brown in wet conditions. The spots join together to form large dark brown patches. In wet conditions, white cottony growths on the underside of leaves are visible. If untreated, affected plants die quickly (within a week) and produce a bad smell.

Background

Late blight of tomato.
Edward Sikora, Auburn University (CC BY)
The disease can survive on living plants and, for a short time, in the soil. Wind and water can spread the disease from infected to healthy plants. Disease attack is favoured when it is warm (15-20°C) and wet. In the field, late blight only has 2 main hosts, tomato and potato. Late blight can survive from one season to the next in infected tomato seeds. Nitrogen fertilizer and irrigation promotes more vegetative growth, making the plant more susceptible to disease attack. The disease can infect tomatoes at any time during the growing season.

Management

Symptoms of late blight on tomato plant.
Edward Sikora, Auburn University (CC BY)
Use clean seed and resistant varieties (e.g. Naqeeb available from AARI, FSD)
Remove and destroy infected leaves and fruits (be sure to wash your hands afterwards) during the crop season and after harvest
Crop rotation for at least four years with crops like maize, millet, sunflower or pumpkin
Avoid heavy use of nitrogen fertilizer to avoid disease
Keep separate fields for early and late crops to slow down the spread of disease
Chlorothalonil 250g/acre during wet weather conditions
Copper oxychloride 3-4g/litre of water when leaves are wet due to dew. Apply at 7-10 day intervals with maximum 3-4 applications per season.
Cymoxanil 60DF @ 250g/100L water/acre, metalaxyl + mancozeb 68WP @ 250g/100L water/acre and dimethomorph 50WP @ 250g/100L water/acre apply at 10-14 day intervals with maximum 3 applications per season in wet weather condition.
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.

Information & Authors

Information

Published In

cover image PlantwisePlus Knowledge Bank
Factsheets for Farmers
Plantwise Factsheets for Farmers

Applicable geographic locations

Asia,  Pakistan

History

Issue publication date: 1 January 2013
Published online: 29 January 2015

Language

English

Authors

Affiliations

Y. S. Khan
Plantwise Faisalabad Pakistan

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