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SUSVEG-Asia Tomato Diseases

Infested tomato leaf

Tomato (Lycopersicon esculentum Mill)
Family : Solanaceae

Tomato is susceptible to a wide range of diseases.  Given the high probability of attack in hot humid conditions and fields with a history of disease, bacterial wilt for example, farmers should take precautionary action by selecting good quality treated seed, using raised, solarized nursery beds and apply biopesticides to the main field. 

There are a number of species of Trichoderma that are utilised as biopesticides, notably T. harzianum, T. polysporum, T. virens and T. viride. In recent years T. viride has increased enormously popularity in India.  Supplied as a wettable powder this antagonistic fungus can be applied as a seed dressing, soil amendment or foliar spray.  T. viride acts by competing with pathogenic fungi for space and nutrients and parasitizes some of them.  Available in sealed sachets of different quantities it can be stored for up to 1 year at temperatures below 40oC.  T. viride is considered to be extremely safe to animals, fish and birds and is not phytotoxic.  Metabolites are thought to assist seed germination and are available as plant nutrients.  Seed coatings are prepared by mixing with a slurry of T. viride (4-5 g per kg of seed).  As a soil amendment T. viride should be mixed with FYM (1 kg to 1 tonne FYM) in the shade and covered with straw or grass for 14 days to multiply, then add to the main FYM (typically 25 tonne per ha) and apply to the main field and plough in.  Foliar spray at the rate of 2.5 kg per ha. 

Pseudomonanas fluoresens is a naturally-occurring bacterium.  Many strains have been isolated and commercialised for use with anti-bacterial and anti-fungal activity similar to that of T. viride. Some manufactures recommend the use of P. fluoresens against bacterial diseases notably bacterial wilt.  Application levels are similar to that of T. viride

Note: If biopesticides are applied their performance will be adversely affected by use of conventional fungicides which should only be used as a last resort.

Disease

Symptoms and treatment

Bacterial wilt
Ralstonia solanacearum

Increasingly important soil borne disease associated with solanaceous crops.  Bacteria can survive in soil for long periods

Control: Introduce rotations with solaneous crops (tomato, brinjal, chilli, potato, capsicum) with non-solanecous crop.  Best affected by using resistant varieties or root stock.

Blossom end rot

Characterised by black patches on immature fruit. Disease associated with calcium deficiency.  

Control: Apply lime before planting.  Once disease is established spray with calcium chloride (2 g per litre) and if available, apply calcium ammonium nitrate fertiliser. 

Damping off
Caused by a range of pathogens.

Common in the nursery when plants wilt and die. 

Control: Seed treatment with Trichoderma viride (2 g per kg of seed.  Ideally solarize the nursery bed before planting.

Buck eye rot
Phytophthora parasitica

Important disease of unripe fruits during the rainy season.  Appears as black spots which enlarge to series of light brown concentric rings. 

Control: Removal of infected leaves slows the disease progress otherwise spray with copper oxychloride (3 g per litre).

Early blight
Alternaria solani

Small black spots on leaves which increase in size and number over time with a yellow edge.

Control:  Mancozeb and chlorothalonil (3 g per litre) effective.

Fusarium wilt
Fusarium oxysporum

Becomes apparent with yellowing of lower leaves.  Slowly spreads to top leaves as lower leaves die off eventually killing the plant. 

Control: Soil treatment with Trichoderma viride

Late blight
Phytophthora infestans

Severe disease during rainy season. Leaves develop purple, brown and black spots. 

Control:  Mancozeb or chlorothalonil (3 g per litre) effective.

Leaf curl virus

Major disease of summer crop and project target discussed in detail [link]. 

Powdery mildrew
Laveillula taurica

White powdery patches on leaves.  Particularly prevalent during periods of high humidity and when crop growth is dense. 

Control: Foliar spray of Triderma viride (2.5 kg per ha). Two application of dinocap (1 ml per litre). 

Spotted wilt

Characterised by black spots on the top leaves which gradually dry.  Flower and fruit production are greatly retarded and the plant eventually dies.

Control: No resistant varieties or conventional control methods available.  Infected plants should be removed and destroyed.  Some researchers recommend spraying with neem seed powder extract (4%).

 

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