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Horticultural crops :: Vegetables:: Tomato

Late blight:  Phytophthora infestans 

Symptoms

  • Water-soaked black lesions on leaves and stems
  • Lesions expand rapidly and the entire leaf becomes necrotic.
  • White sporulation (sporangia and sporangiophores) on leaves.

Fruit

  • Dark brown lesions on fruit
  • Soft rot and disintegration of fruits.


Symptoms on leaves

Fruit infection

Sporangiophores and sporangium

Oospore

Causal organism

  • Phytophthora infestans (Mont.) de Bary

Asexual spores :

  • Indeterminate sporangiophores, Zoospores: Biflagellate with one tinsel flagellum directed anteriorly and one whiplash flagellum directed posteriorly

Pathogen:

  • Hyaline and coenocytic

Sexual spores :

  • Thick-walled oospore

Survival and Mode of Spread

Survival :

  • Infected Debris

Primary spread:

  • Infected debris

Secondary spread:

  • Wind

Favourable conditions :

  • Cool nights, warm days and extended wet conditions from rain and fog
  • Sporangia formed when RH is < 90%
  • Optimum temp for sporulation is 18 - 22oC

Integrated Disease Management:

  • Proper drainage
  • Crop rotation
  • Soil application of Trichoderma asperellum (viride) @ 1.0 kg/ac
  • Spray Cyazofamid 34.5% SC @ 80 ml/ac or Azoxystrobin 23% SC @ 200 ml/ac or Mancozeb 35% SC @ 1000 g/ac or Zineb 75% WP @ 800 g/ac or Azoxystrobin 18.2%+ Difenoconazole 11.4% SC @ 200 ml/ac

Source of Information

  • https:www.apsnet.org.
  • Crop production guide – Horticulture 2020
  • Acknowledgement

  • Dr.N.Indra, Associate Professor, Department of Plant Pathology, TNAU, Coimbatore
  • Dr.P.Renukadevi, Professor, Department of Plant Pathology, TNAU, Coimbatore.

    Updated on Jan 2023


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