Pacific Pests, Pathogens, Weeds & Pesticides - Online edition

Pacific Pests, Pathogens, Weeds & Pesticides

Ringwom blong wotamelen (Watermelon gummy stem blight) (007)

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Photo 1. The large black spots are typical of gummy stem blight, Didymella bryoniae, on the leaves. Notice the concentration of the spots at the margins of the leaf where water stays for longer. Some of the spots have joined together.

Photo 2. This is typical of the defoliation that occurs with gummy stem blight infection, making it a serious disease. Leaves go yellow, collapse and die when they have only a few spots. The older leaves die first.

Diagram. Life-cycle of gummy stem blight, Didymella bryoniae.

Samari

  • Oli faenem olbaot long wol, long wotamelen, rokmelon mo kukamba (luk Fact Sheet no. 201). Hemi wan rabis sik. Ol spot oli stat kamaot long ol lif mo oli kam plante kwiktaem, ol lif oli kam blak mo oli drae afta oli ded. I gat wan stiki kaen wota we i stap kamaot long olgeta spot we oli stap long rop blong hem.
  • Ol spo (spores) we oli stap long olgeta blak poket (sacs) ia oli spred tru long win mo ren.
  • Kontrolem wetem fasin blong faming: neseri i mas stap longwe long prodaksen eria; sterelaesem graon o miks blong ol narafala kaen material, we i no graon; jekem wanwan sidling sipos i gat ol spot, mo rimuvum sipos yu luk; jensem o roteitem ol krop evri tri yia; yu no mas plan klosap long ol wotamelen we oli sik; kolektem mo bonem ol toti afta we yu havest.
  • Kontrolem wetem kemikol: coppers, mancozeb, o chlorothalonil evri 7-10 dei, dipen long weta.

Komon nem: Gummy stem blight

Saentifik nem: Stagonosporopsis cucurbitacearum; (bifo oli singaotem ‘Didymella bryoniae’). I gat tu nem blong hem taem we hemi stap long aseksual stej, Phoma cucurbitacearum o Ascochyta cucumis. Las kaen ia, oli save faenem long olgeta plant long fil, we oli stap prodiusum ol smolsmol oval spore long ol raon blak strakja long lif, we oli kolem 'pycnidia' we klosap bae man ino save luk wetem neked ae blong hem.

Photo 3. Gummy stem blight infection, Didymella bryoniae, on a seedling. It is just possible to see the black dots that contain the spores in the centre of the spot. Infection of seedlings in the nursery is a major threat to watermelon production as it means the fungus is taken to the field and early infection and spread is guaranteed.

Photo 4. Checking in the nursery for infections of gummy stem blight, Didymella bryoniae, on seedlings of watermelon. This should be done at least twice a week. If infections are found, the plants should be removed and burnt. Notice that the nursery is high above ground.

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