BLACK ROT: Pythium Ultimum

Ailments Orchid Doctor

by Robert M. [Bert] Hamilton (Compiler)

Originally published in The Orchid Doctor in 1980 and 1988

Posted by Sys Admin over 7 years ago.

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Most destructive of cattleyas, others are susceptible; similar symptoms to Phytophora cactorum; small water-soaked spots, later turn purplish black; yellow margin advances; spread quite rapid, 2 or 3 inches per day; often following dividing of plants; spread by splashing; dip for 60 minutes in Natriphene; use Tersan as preventive. B9; BU10; OR74-234
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  1. Stefan Neher
    about 4 years ago
    Is there a similar pythium or Phytophora that attack Phaius orchids? A very distinctive, bleu-cheese vein color appeared inside the vascular bundles in my Phaius inflorescences, turning black and mushy everything at nodes. Left behind were somewhat sparkling, furry-looking structures where the peduncle had once been attached.

More The Orchid Doctor Articles under the Heading Black Rot

Black Rot Comments
BLACK ROT: Caused by Fungi Pythium ultimum and Phytophora cactorum Most destructive to cattleya-types; worst during cool months; purplish brown area on leaf or root and rhizome and upward into pseudobulbs; drench with Truban 1/2 tpg. AH16 0
BLACK ROT: Fungicide as Preventive Dexon-35 can be so used; also, Truban; packages are commercial size, try to obtain from a commercial grower. A74-896 0
BLACK ROT: In New Leads of Potinara; Benlate and Natriphene Did Not Control Use 1/2 tpg. drench of either Dexon-35, Truban, Terrazole or Banrot; commercial greenhouses may sell a few spoonfuls of one of them. A75-500 0
BLACK ROT: Leads Go Black, Leaves Change to Lighter Color and Wrinkle; Pseudobulbs Wrinkle and Show Brown Patches Truban is effective; cut off all diseased parts; plunge all into solution 1 tpg. A74-1062 0
BLACK ROT: Leaves on Cattleyas Develop Black Spot At Top, Eventually Killing Leaf and Sheath Use Dexon-35 or Truban, 1 tpg. as an overall drench, or soak for 20 to 30 minutes; repeat in 14 days. A72-905; A79-1112 0
BLACK ROT: On Cattleyas Control with Truban or Dexon-35; Truban is gaining favor over Dexon-35; drench or soak in 1 tpg. A72-341; A75-680; A79-1112; use Tersan or Fermate. S198 0
BLACK ROT: On One-inch New Growths This indicates a root disease; dip in Banrot solution ltpg., before repotting; another fungicide to try is Subdue, which may be effective. A81-393; RMH 0
BLACK ROT: On Specimen Cattleya; Benlate Does Not Cure Black rot is not cured by Benlate, use Dexon-35, 1 tpg. soak for 20 minutes. A74-217 0
BLACK ROT: Phytophora Cactorum Leaf and heart rot; cattleyas are the main host; fungus attacks all parts except roots; shows purple, purplish brown or black; leaves often become brittle and can be jarred off; caused by coolness and high humidity; cure must include introducing agent inside plant tissue; use Natriphene dip for 60 minutes, or Dexon 70%, or Thiram 75% (Tersan) WP, at rates given for 100 gallons; repeat in one month; Physan and Shield are good for seedlings; avoid overhead watering. B7; BU8+ 0
BLACK ROT: Pythium Sp. of Fungi On cattleyas; cut rot away ruthlessly; burn the compost; immerse plant in Orthocide captan at 1 teaspoon to 1 pint water for one hour. OR76-99 0
BLACK ROT: Tips of New Cattleyas Turn Brown Caused by a fungus; remove all infected growth; soak pot and plant in 1/2 tpg. Dexon-35 or Benlate. A72-686; F69-94 0
BLACK ROT: Treatment with Dexon Remove diseased parts; soak or drench pot in one teaspoon per two gallons water three or four times at 10 to 14 day intervals; it is surface effective only. A74-969 0
BLACK ROT: Two Kinds Are Prevalent One is a cool-weather rot, the other is a warm-weather type and both cause blackening of leaf tissue; both are contagious and can be spread by splashing water; keep plants dry, spray with Benlate; the summer type can destroy a plant in three days, in some areas. OR85-69; F81-17 0
BLACK ROT: Water Mold Pythium Ultimum Is the Cause The special enemy of commumity pots of seedlings; damp-off; spray with Physan, Anti-Damp, or Natriphene once a month as preventive; on mature plants cut out rot; soak plant in good fungicide, dry, treat with Tersan; illus. A66-399+; A73-811 0

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