Diseases of Tomato

Diseases of Tomato

Damping off: Pythium aphanidermatum

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.

http://agritech.tnau.ac.in/org_farm/tomato%20damping%20off.jpg

Mode of spread and survival

  • All the causal organisms are soil inhabitants and they build up in soil with the available hosts.
  • Generally these pathogens have wide host range.

Management

  • Used raised seed bed.
  • Provide light, but frequent irrigation for better drainage.
  • Drench with Copper oxychloride 0.2% or Bordeaux mixture 1%. Seed treatment with fungal culture Trichoderma viride (4 g/kg of seed) or Thiram (3 g/kg of seed) is the only preventive measure to control the pre-emergence damping off.
  • Spray 0.2% Metalaxyl when there is cloudy weather

Fusarium Wilt: Fusarium oxysporum f. sp. lycopersici

Symptom

  • The first symptom of the disease is clearing of the veinlets and chlorosis of the leaves.
  • The younger leaves may die in succession and the entire may wilt and die in a course of few days.
  • Soon the petiole and the leaves droop and wilt.
  • In young plants, symptom consists of clearing of vein let and dropping of petioles.
  • In field, yellowing of the lower leaves first and affected leaflets wilt and die.
  • The symptoms continue in subsequent leaves.
  • At later stage, browning of vascular system occurs.
  • Plants become stunted and die.

http://agritech.tnau.ac.in/org_farm/fusarium_wilt_race3.jpg

Pathogen

  • Mycelium is septate and hyaline.
  • They produce macro and micro conidia.
  • Micro conidia are one celled, hyaline, ovoid to ellipsoid.
  • Two races of pathogen have been identified.

Mode of spread and survival

  • The fungus is seed borne and soil borne.
  • The fungus survives in the soil as chlamydospores or as saprophytically growing mycelium in infected crop debris for more than 10 years.
  • One of the chief methods of its distribution is by seedlings raised in infected soil.
  • Wind borne spores, surface drainage water and agricultural implements also help in distribution of the pathogen from field to field.

Management

  • The affected plants should be removed and destroyed.
  • Spot drench with Carbendazim (0.1%).
  • Crop rotation with a non-host crop such as cereals.

Early Blight : Alternaria solani

Symptoms

  • This is a common disease of tomato occurring on the foliage at any stage of the growth.
  • The fungus attacks the foliage causing characteristic leaf spots and blight.
  • Early blight is first observed on the plants as small, black lesions mostly on the older foliage.
  • Spots enlarge, and by the time they are one-fourth inch in diameter or larger, concentric rings in a bull’s eye pattern can be seen in the center of the diseased area.
  • Tissue surrounding the spots may turn yellow.
  • If high temperature and humidity occur at this time, much of the foliage is killed.
  • Lesions on the stems are similar to those on leaves, sometimes girdling the plant if they occur near the soil line.
  • Transplants showing infection by the late blight fungus often die when set in the field.
  • The fungus also infects the fruit, generally through the calyx or stem attachment.
  • Lesions attain considerable size, usually involving nearly the entire fruit; concentric rings are also present on the fruit.

http://agritech.tnau.ac.in/crop_protection/crop_prot_crop%20diseases_veg_tomato_clip_image008.jpg

Pathogen

  • Mycelium is septate, branched, light brown which become darker with age.
  • Conidiophores are dark colored.
  • Conidia are beaked, muriform, dark colored and borne singly.

Mode of spread and survival

  • The pathogen is spread by wind and rain splashes.
  • Under dry conditions it survives in infected plant debris in the soil for upto three years and is also seed borne.

Management

  • Removal and destruction of crop debris.  
  • Practicing crop rotation helps to minimize the disease incidence.
  • Spray the crop with Mancozeb 0.2 % for effective disease control.

Septoria Leaf Spot:Septoria lycopersici

Symptom

  • The plant may be attacked at any stage of its growth.
  • The disease is characterized by numerous, small, grey, circular leaf spots having dark border.

http://agritech.tnau.ac.in/crop_protection/crop_prot_crop%20diseases_veg_tomato_clip_image017.jpg

Pathogen

  • Mycelium is septate, branched, hyaline when young and darkens with age.
  • Pycnidia are erumpent.
  • Pycnidiospores are filiform, hyaline and septate.

Mode of spread and survival

  • The pathogen is spread by wind and rain splashes, insects and on the hands and clothings of tomato pickers.
  • It survives from one season to the next on infested crop debris and also on solanaceous weeds.
  • The fungus also survives on or in the seed.
  • Seed stocks contaminated with spores produce infected seedlings.

Management

  • Removal and destruction of the affected plant parts.
  • Seed treatment with Thiram or Dithane M-45 (2 g/kg seed) is useful in checking seed borne infection.
  • In the field spraying with Mancozeb 0.2 % effectively controls the disease.

Bacterial wilt: Burkholderia solanacearum

Symptom

  • This is one of the most serious diseases of tomato crop.
  • Relatively high soil moisture and soil temperature favour disease development.
  • Characteristic symptoms of bacterial wilt are the rapid and complete wilting of normal grown up plants.
  • Lower leaves may drop before wilting.
  • Pathogen is mostly confined to vascular region; in advantage cases, it may invade the cortex and pith and cause yellow brown discolouration of tissues.
  • Infected plant parts when cut and immersed in clear water, a white streak of bacterial ooze is seen coming out from cut ends.

http://agritech.tnau.ac.in/crop_protection/crop_prot_crop%20diseases_veg_tomato_clip_image021.jpg

Pathogen

  • The bacterium is gram negative, rod shaped often occurs in pairs, motile with 1 – 4 flagella.The optimum temperature for growth is 30 – 37˚C.

Mode of spread and survival

  • The bacterium survives in soil and they spread through irrigation water and by transplanting of infected seedlings.
  • The bacterium survives for 3 years in fallow and for a unlimited period in cultivated land.
  • Chilli, egg plant, grount nut, potato and tobacco are alternative hostswhich help it to survive between tomato crops.

Management

  • Avoid damage to seedling while transplanting.
  • Apply bleaching powder @ 10kg/ha. 
  • Crop rotations, viz., cowpea-maize-cabbage, okra-cowpea-maize, maize- cowpea-maize and finger millet-egg plant are reported effective in reducing bacterial wilt of tomato.

Bacterial Leaf Spot : Xanthomonas campestris pv. vesicatoria

Symptom

  • Moist weather and splattering rains are conducive to disease development.
  • Most outbreaks of the disease can be traced back to heavy rainstorms that occur in the area.
  • Infected leaves show small, brown, water soaked, circular spots surrounded with yellowish halo.
  • On older plants the leaflet infection is mostly on older leaves and may cause serious defoliation.
  • The most striking symptoms are on the green fruit.
  • Small, water-soaked spots first appear which later become raised and enlarge until they are one-eighth to one-fourth inch in diameter.
  • Centers of these lesions become irregular, light brown and slightly sunken with a rough, scabby surface.
  • Ripe fruits are not susceptible to the disease.
  • Surface of the seed becomes contaminated with the bacteria, remaining on the seed surface for some time.
  • The organism survives in alternate hosts, on volunteer tomato plants and on infected plant debris.

Tomato Leaf Spot

Pathogen

  • The bacterium is gram negative, short rod shaped and has a single, polar flagellum.
  • Capsules are formed.

Mode of spread and survival

  • The pathogen survives in the diseased plant debris, volunteer plants.
  • It is seed borne.
  • The bacterium enters through stomata or injuries and lenticels.
  • Secondary spread through rain splashes.
  • Disease spreads to new areas through infected seeds and diseased transplants.

Management

  • Disease-free seed and seedlings should always be used and the crop should be rotated with non-host crops so as to avoid last years crop residue.
  • Seed treatment with mercuric chloride (1:1000) is also recommended for control of disease.
  • Spraying with a combination of copper and organic fungicides in a regular preventative spray program at 5 to 10 day intervals or Spraying with Agrimycin-100 (100 ppm) thrice at 10 days intervals effectively controls the disease.

http://www.gardenaction.co.uk/images/mosaic_virus_tomato.jpg

Mosaic: Tomato mosaic virus (TMV)

Symptom

  • The disease is characterized by light and day green mottling on the leaves often accompanied by wilting of young leaves in sunny days when plants first become infected.
  • The leaflets of affected leaves are usually distorted, puckered and smaller than normal.
  • Sometimes the leaflets become indented resulting in “fern leaf” symptoms.
  • The affected plant appears stunted, pale green and spindly.
  • The virus is spread by contact with clothes, hand of working labour, touching of infected plants with healthy ones, plant debris and implements.

Pathogen

  • Virus paricles are rod shaped, not enveloped, usually straight and thermal inactivation point is 85 – 90˚C.

Mode of spread and survival

  • The virus is seed borne and upto 94% of seeds may contain the virus.
  • The virus infection occurs during transplanting It is readily transmissible.
  • Many solanaceous plants are susceptible to tomato mosaic virus.
  • The virus is spread easily by man and implements in cultural operations or by animals and by leaf contact.

Management

  • Seeds from disease free healthy plants should be selected for sowing.
  • Soaking of the seeds in a solution of Trisodium Phosphate (90 g/litre of water) a day before sowing helps to reduce the disease incidence.
  • The seeds should be thoroughly rinsed and dried in shade.
  • In the nursery all the infected plants should be removed carefully and destroyed.
  • Seedlings with infected with the viral disease should not be used for transplanting.
  • Crop rotation with crops other than tobacco, potato, chilli, capsicum, brinjal, etc. should be undertaken.

Leaf curl: Tomato leaf curl virus (ToLCV)

Symptom

  • Leaf curl disease is characterized by severe stunting of the plants with downward rolling and crinkling of the leaves.
  • The newly emerging leaves exhibit slight yellow colouration and later they also show curling symptoms.
  • Older leaves become leathery and brittle.
  • The nodes and internodes are significantly reduced in size.
  • The infected plants look pale and produce more lateral branches giving a bushy appearance.
  • The infected plants remain stunted.

http://www.avrdc.org/LC/tomato/tylcv05big.jpg

Pathogen

  • The virus particles are 80nm in diameter.

Mode of spread and survival

  • It is neither seed nor sap transmissible.
  • But seeds from fresh fruits having infection may have the virus on the seed coat.
  • The virus is transmitted by white fly, Bemisia tabaci and grafting.
  • Even a single viruliferous insect is able to transmit the virus.

Management

  • Keep yellow sticky traps @ 12/ha to monitor the white fly.
  • Raise barrier crops-cereals around the field.
  • Removal of weed host.
  • Protected nursery in net house or green house.
  • Spray Imidachloprid 0.05 % or Dimethoate 0.05% @ 15, 25, 45 days after transplanting to control vector.

Spotted wilt: Tomato spotted wilt disease (TSWV), Groundnut bud necrosis virus

Symptom

  • It causes streaking of the leaves, stems and fruits.
  • Numerous small, dark, circular spots appear on younger leaves.
  • Leaves may have a bronzed appearance and later turn dark brown and wither.
  • Fruits show numerous spots about one-half inch in diameter with concentric, circular markings.
  • On ripe fruit, these markings are alternate bands of red and yellow.

http://agritech.tnau.ac.in/org_farm/tlc.jpg

Pathogen

  • It is isometric particles of 70 – 90nm diameter.
  • Thermal inactivation point is 40˚C.

Mode of spread and survival

  • The spotted wilt virus is transmitted through thrips (Thrips tabaci, Frankliniella schultzi and F. occidentalis).

Management

  • The affected plants should be removed and destroyed.
  • Alternate or collateral hosts harboring the virus have to be removed.
  • Raise barrier crops – Sorghum, Maize, Bajra 5-6 rows around the field before planting tomato.
  • Spray Imidachloprid 0.05% or any systemic insecticide to control the vector.

Gray Mould: Botrytis cinerea

Symptoms

  • Lesion – a watery area with a light brown or tan-colored central region.
  • Converted into a soft, watery mass within a few days.
  • Skin is broken, the grayish mycelium and spore clusters develop within a few hours.
  • Halo forms around the point of entry -small whitish rings approximately – develop on young green fruit.
  • “Ghost spots” are usually single rings but may be solid white spots; the center of which contain dark-brown specks.

Pathogen

  • Mycelium is septate and branched, hyaline but become dark in color upon age.
  • Conidiophores are branched and bear conidia at the apex.
  • Conidia are continuous or one septate, oblong and dark.

Mode of spread and survival

  • High relative humidities are necessary for prolific spore production.
  • Optimum temperatures for infection are between 65° and 75° F (18° and 24° C), and infection can occur within 5 hours.
  • High temperatures, above 82° F (28° C), suppress growth and spore production.

Management

  • Spraying with Bordeaux mixture 1.0 % or mancozeb 0.2% is helpful in reducing the disease.
  • Resistant varieties like Vetomold may be grown in area’s where disease appears in an endemic form.
  • Eurocross varities like Antincold, LMRI and Sapsford’s No.1 are resistant.

Early Blight : Alternaria solani

Symptoms

  • The fruit become infected-through the calyx or stem attachment, either in the green or ripe stage.
  • Concentric ring present on the fruit surface.
  • Appear leathery and may be covered by a velvety mass of black spores.
  • Infected fruit frequently drop, and losses of 50% of the immature fruit may occur.

Pathogen

  • Mycelium is septate, branched, light brown which become darker with age.
  • Conidiophores are dark coloured. Conidia are beaked, muriform, dark colored and borne singly.
  • In each conidium 5 – 10transverse and a few longitudinal septa are present.

Mode of spread and survival

  • The pathogen is spread by wind and rain splashes.
  • Under dry conditions it survives in infected plant debris in the soil for upto three years and is also seed borne.

Management

  • Disease free seeds should be used for sowing.
  • Seeds soaked in thiram 0.2% at 30˚C for 24h gives better protection.
  • Seed treatment with thiram 2g/ kg gives good protection against seed borne infection.
  • Three sprayings with difolatan 0.2% or mancozeb at fortnightly interval prevent the spread of the disease.
  • Infected plant debris should be removed.
  • Three year rotation with non solanaceous crop is recommended.

Bacterial Soft Rot and Hollow Stem: Erwinia carotovora pv. carotovora

Symptoms

  • Fruit -soft watery decay of fruit, starting at one or more points, as very small spots.
  • Enlarge-very rapidly until the entire fruit -soft watery mass.
  • Pathogen liquefies fruit tissue by breaking down the pectate “glue” that holds plant cells together Leakage-internal collapse resembling a shriveled water balloon.
  • Bacteria -single-celled – rapidly multiply and spread-in water. During wet weather and High humidity, Heavy rain fall or irrigation.
  • Warm temperatures in the 73 – 95 F. range

gray mold on tomato Tomato Phytophthora

Phoma Rot: Phoma destructive

 Symptoms

  • Distinguished from other rots by the black color of this spot.
  • Small, black, pimple-like eruptions.
  • Specks are the pycnidia or fruiting bodies of the fungus.
  • Moderate temperature and high humidity.

Pathogen

  • The ascospores are irregularly arranged in two series.
  • They are ellipsoid with obtuse ends, hyaline and guttulate.
  • Pycnidia are solitary to gregarious and dark brown.
  • Conidia typically biguttulate, straight and irregular.

Mode of spread

  • The pathogen is seed borne.

Management

  • Seed treatment with organomercurial and spraying the crop with zineb 0.2% gives adequate protection against the disease.

 

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