Posted by: marinvit | June, 2010

Orchid Diseases – Fungal rots

  • – can cause death if not controlled
  • – root & rhizome rots – rhizoctonia & fusarium
  • – brown spot leaf rots – pseudomonas
  • – black rots on pseudobulbs- phytophthora & pythium

Causes & Symptoms

Black rotsactually are fungi

– prevalent in cool months & high humidity
– leaf or new growth turn purplish brown surrounded by yellow, quickly spreads to rhizome and further growths, leaf may fall at slight touch

Root rots

– affects plants of any age

– from broken down bark mediums

– poor drainage

– usually confined to roots except small seedlings

– wilting of the plants & shrivelling of pseudoblubs

– yellowing & twisting of leaves

Fusarium wilt

– usually confined to root & rhizomes

– thru cut ends of divided plants

– die within 3-9 weeks , may take a year

– yellow thin shrivelled & twisted leaves

– roots rotten

– rhizome has purple ring & pink tissue in cross section

Bacterial Rots

– usually cause death of plants

-brown spots & rots pseudomonas & erwinia


Symptoms:

bacterial brown spotpseudomonas sp.

– soft water soaked lesion turning brown or black

-advances rapidly

-exudate on leaf containing bacterial

brown roterwinia cypripedii – mostly in paphs

– water soaked spots near middle of leaf

– spot darkens to chestnut brown

– spots enlarging fairly rapidly

– plants become shrivelled mass

soft roterwinia carotovora – infrequent outbreaks

–  enter through wounds

–  wet rot with offensive odour

– rapid spread in roots & leaves & new shoots

– slower in pseudobulbs & rhizomes

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