Tomato Diseases PDF

DISEASES OF TOMATO  Damping Off of Seedlings: Damage symptoms Damping off of tomato occurs in two stages, i.e. the pre-emergence and the post- emergence phase. In the pre-emergence the phase the seedlings are killed just before they reach the soil surface. The young radic...

DISEASES OF TOMATO  Damping Off of Seedlings: Damage symptoms Damping off of tomato occurs in two stages, i.e. the pre-emergence and the post- emergence phase. In the pre-emergence the phase the seedlings are killed just before they reach the soil surface. The young radical and the plumule are killed and there is complete rotting of the seedlings. The post-emergence phase is characterized by the infection of the young, juvenile tissues of the collar at the ground level. The infected tissues become soft and water soaked. The seedlings topple over or collapse. It can be caused by several different fungi (Pythium, Rhizoctonia or Phytophthora) which attack tomato seeds, tender stems, and roots. Tomatoes are most affected in humid conditions, especially if the soil is cold and wet. Young seedlings or plants are most susceptible. An epidemic of damping off disease can be a disastrous way to begin a new tomato season. Although fungi live in the soil and water, spores spread through the air and can move quickly from one seed tray (or garden row), to another. Affected plants appear as if they have been cut off at the base. Favourable conditions Seedlings during the first three weeks after sowing are susceptible planting in heavily infested soil overwatering or poor drainage overcrowding or poor ventilation of seedlings excess application of nitrogen stressful environmental conditions such as cloudy, wet weather that results in etiolated plants, prolonged soil moisture, or low light that prevents drying pathogenic nematodes are present. Survival and spread Primary: Soil, Seed, Water Secondary: Conidia through rain splash or wind. Management: Avoid placing nursery in a shaded, humid place. Select well-draining nursery sites away from tomato fields. Elevate seed beds to improve drainage 6 inches above ground level.. Transplant only disease-free seedlings. Ensure good aeration through spacing of seeds (>5 cm, 2" space) and staking of plants with wooden sticks. Do not overwater. Irrigate early in the day to allow rapid drying of seed beds. Use of fungicide-treated certified seeds. Seed treatment with Thirum 3gm per kg of seed can be used to prevent or control the pre- emergence damping off. Using foliar spray with Metalaxyl @ 0.2% during cloudy weather.  Tomato late blight C.O. Phytophthora infestans Symptoms Infection and symptoms can occur on leaves, stems and tomato fruit. Leaf lesions begin as small necrotic or water-soaked spots that enlarge to form brown lesions or blotches, eventually killing the leaf. The lesions may or may not have a yellow or chlorotic border. Stem infections result in dark brown lesions that have well-defined edges. On tomato fruit, brown lesions are firm and may have a rough or bumpy surface.  Pathogen Phytophthora infestans, is a member of the oomycetes. The mycelium is hyaline and coenocytic (few septa), and the nuclei are diploid. Asexual reproduction P. infestans produces sporangia on sporangiophores. The sporangiophores are indeterminate. (i.e., they grow and produce sporangia continuously). P. infestans is one of the few species in the genus Phytophthora adapted to air dispersal. Sporangia may be dispersed to neighbouring fields, but do not generally survive long-distance travel because of desiccation and exposure to solar radiation. In cool, wet conditions, zoospores will form and emerge from the sporangia after about two hours.  In warmer conditions, sporangia may function as a single spore and germinate directly. Zoospores are biflagellate (have two flagella) with one tinsel flagellum directed anteriorly and one whiplash flagellum directed posteriorly. After swimming on the surface of the host plant surface, zoospores encyst and infect the plant. Disease Cycle In the absence of the oospore stage, Phytophthora infestans survives in different crops and also infected fruits and seeds, also in infected crop residue. Sporangia may be produced on the infected fruits or crop residues, spread through air currents to the new crops and also through rain splashes and through heavy dew. MANAGEMENT Tomato varieties resistant to certain races of the late blight fungus Remove any nearby volunteer tomato and potato plants and nightshades. Avoid sprinkler irrigation, if possible, because it favors the development of late blight. Fungicides are generally needed only if the disease appears during a time of year when rain is likely to occur or overhead irrigation is practiced. Metalaxyl-resistant strains of the pathogen are widespread in California and this fungicide is no longer effective. MANCOZEB + CYMOXANIL mixture @1.5g/l of water can reduce the spread of the disease. AZOXYSTROBIN + DIFENOCONAZOLE @ 1ml/l of water Mancozeb 75WP @2.5g/l of water also check the spread of the disease.  Early Blight of Tomato- Alternaria solani Symptoms Leaves Initially small dark spots form on older foliage near the ground Leaf spots are round, brown, larger spots have target like concentric rings and tissue around spots often turns yellow Severely infected leaves turn brown and fall off, or dead. Stem Seedling stems are infected at or just above the soil line. The stem turns brown, sunken and dry (collar rot). If the infection girdles the stem, the seedling wilts and dies. Stem infections on older plants are oval to irregular, dry brown areas with dark brown concentric rings. Fruit Fruit can be infected at any stage of maturity Fruit spots are leathery, black, with raised concentric ridges and generally occur near the stem Infected fruit may drop from the plant  Survival and spread Primary: The fungus spends the winter in infected plant. It can also be seed borne. Secondary: The spores are transported by water, wind, insects, other animals including man, and machinery. Favourable conditions Disease develops at moderate to warm (59 to 80 F) temperatures; 82 to 86 F optimum, rainy weather or heavy dew, more than 90% humidity. Management Remove and destroy infected leaves (be sure to wash your hands afterwards). Treat with copper fungicide spray. You can apply until the leaves are dripping, once a week and after each rain. The best chemical fungicide for tomato is chlorothalonil.You may also choose Mancozeb or Maneb, although these have longer wait times before you can harvest tomatoes safely than does chlorothalonil.  Mosaic - Tomato mosaic virus Symptoms The virus causes a light and dark green mosaic mottle with raised dark green area and distorted crinkled younger leaves.  The plants are stunted and leaves may be distorted to a fan leaf or tendril like The symptoms vary depending on the strain of the virus. Some strains cause yellowing or leaf mottling which may also affect the fruit. Some other strains produce streak symptoms consisting of longitudinal necrotic streaks on stem or petioles. Such diseased plants are killed Necrotic sunken lesions also appear on fruits and sometimes internal necrosis or browning of mature fruit occurs. Mode of spread and Survival The virus is seed borne and is sap transmissible The virus is spread easily by man and implements in cultural operations or by animals and by leaf contact. Management All collateral hosts in the vicinity should be destroyed before planting new crop Rouge out and destroy diseased plants Virus free seed should be obtained and used for sowing Cross protection of tomato seedlings by inoculating with mild strains Field workers should avoid using tobacco products while working in the field  Leaf curl (Tobacco leaf curl virus) Symptoms:  Crinkling and curling of leaves, plants stunted, reduction in length of internode.  In severe cases leaves reduced in size with puckering of leaves.  On the lower side of leaves there will be thickening of veins with small leaf lie outgrowths known as enations. Mode of spread: White files (Bemisia tabaci) Seed borne Management : Spray Monocrotophos 15, 25, 45, DAS Favourable Conditions  Rainy days during kharif season show high incidence of disease.  The presence of the weed hosts and other legume hosts. Mode of Spread and Survival  The virus is transmitted by thrips viz., Thrips tabaci and Scirtothrips dorsalis.  The virus survives in weed hosts, tomato, petunia and Chilli. Management  Rogue out infected plants upto 30 days after sowing.  Remove the weed hosts which harbour virus and thrips.  Spray Monocrotophos or Methyl demeton at 500 ml/ha on 30 and 45 days after sowing.