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Plantwise Technical Factsheet

bacterial brown rot of orchids (Pectobacterium cypripedii)

Host plants / species affected
Carica papaya (pawpaw)
Paphiopedilum (lady's slipper orchid)
Phalaenopsis amabilis (moth-orchid)
List of symptoms/signs
Growing point  -  rot
Leaves  -  necrotic areas
Leaves  -  yellowed or dead
Stems  -  dieback
Stems  -  internal discoloration
Whole plant  -  early senescence
Whole plant  -  plant dead; dieback
Symptoms
P. cypripedii causes brown rot on orchids with fleshy leaves. Initial symptoms are small, water-soaked lesions which enlarge to become brown, greasy-looking, slightly sunken areas.

On pawpaws, P. cypripedii causes necrotic water-soaked lesions on leaf blades and stems which progress slowly down into mature tiissue, producing a black rot. Fruit from disease orchards develop black spots (Leu et al., 1980).
Prevention and control
Cultural control and Sanitary Methods

Still air and cool temperatures must be avoided since they can trigger rots caused by P. cypripedii. There must be sufficient ventilation to quickly dry the plants after watering. Compost must be kept dry overnight at a temperature of 18° to 20°C. Humus epiphytic orchid plants of the Section Brachypetalum, like the susceptible species of Paphiopedilum, need oxygen at the roots. They should not be grown in a completely enclosed environment, as they require plenty of moving air.
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