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Post Harvest Diseases:: Vegetables:: Cucurbits

Gummy stem blight  and black spot: Didymella bryoniae
Symptom:
  • Leaf - water-soaked lesion, inter veinal necrotic scorch
  • Lesions - surrounded by a yellow halo, & when spots dry up, they often crack
  • Stems - water-soaked lesions and later appear tan
  • Stem lesions often cause gummy, reddish -brown or black beads to exud
    Black rot
  • Affected area - brownish and water soaked
  • Advanced stages - rind becomes black and deeply wrinkled
  • Large irregular areas of the fruit become bronzed with distinct concentric rings
Black rot of squash Gummy stem blight on squash Black rot of water melon Watermelon gummy stem blight
Brownish gummy exuds from stem on cucurbits Internal discolouration and rotting of cucurbits Severe infection of cucurbit black rot
Identification of pathogen:
  • Pycnidia are produced, giving rise to conidia, which serve as the primary inoculum
  • Young pycnidia appear light brown & as they age become black 
  • Conidia - short and cylindrical, with usually one septum near the middle, or they may be unicellular

Mode of spread and survival:

  • Soil and seed borne
  • Survives as dormant mycelium or as chlamydospores 
  • Under moist conditions, they are readily dispersed by splashing water

Epidemiology:

  • 85%RH
  • Optimal temperature - Watermelon 23.9°C , Muskmelon 39°C
Management:
  • Disease-free seed 
  • 2-year crop rotation out of all cucurbits
  • Field sanitation
  • Fungicides - chlorothalanil, mancozeb and benomyl
  • Cucumbers - precooled to 10oc or lower temp
Source of Images:
http://content.ces.ncsu.edu/gummy-stem-blight-and-phoma-blight-on-cucurbits/
http://www.plantmanagementnetwork.org/elements/view.aspx?ID=6130
http://vegetablemdonline.ppath.cornell.edu/PhotoPages/Cucurbit/Gummy/GSBfs4.htm
www.omafra.gov.on.ca/english/crops/facts/09-051w.pdf

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