Control of late blight disease in tomato
Late blight, caused by a fungus Phytophthora infestans, is one of the most devastating diseases of potato and tomato worldwide.
It first appears on the leaves and stems, and later on the fruits. Symptoms appear on leaves as pale green, water-soaked spots, often beginning at leaf tips or edges. The circular or irregular leaf lesions are often surrounded by a pale yellowish-gree
n border that merges with healthy tissue.
White mould growth
Lesions enlarge rapidly and turn dark brown to purplish-black. During periods of high humidity and leaf wetness, a cottony, white mould growth is usually visible on the lower leaf surface at the edges of lesions. In dry weather, infected leaf tissues quickly dry up and the white mould growth disappears.
Infected areas on stems appear brown to black and entire stem may be killed in a short time when moist weather persists.
Fruit lesions
The fungus produces grey-green water-soaked spots which enlarge, coalesce, and darken, resulting in large, firm, brown, leathery-appearing lesions on fruits.
Cool nights and warm days with moist weather, which prevail during October-November, are the best conditions for development of the disease. Rain, fog or heavy dew are also ideal.
Some management tips
— The disease is soil borne and can be managed by using integrated approaches to crop production and protection.
— Plant only healthy tomato transplants. Check to make sure plants are free of dark lesions on leaves or stems.
— Planting at recommended space (100 x 60cm), raising the crop in raised beds, removing infected fruits and staking of plants to avoid contact of fruits with soil for good air circulation is advisable.
— Spray at regular intervals. Begin chemical control programs before symptoms appear.
Copper hydroxoide(2g/lit) chlorothalonil (2g/liter) and mancozeb (2.5 g/liter) fungicides are the standard protectants used for control. They are usually applied every seven to ten days for best protection.
P.Chowdappa
Girija Ganeshan
& N.Ramachandran
Division of Plant Pathology
Indian Institute of
Horticultural Research
Bangalore
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