CAMP LOT A NOISE TROPICALS

CLAN Tropicals

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COMMON ROTS

What to do when your plant falls victim

Please realize that this informational sheet is necessarily general. It is not meant to be a definitive answer to orchid rots. It is posted here in the hopes that our past experiences may help some other orchid grower. Please use this page as a starting point to identify the general problem area, so a specific treatments may be started. To download this page for future reference, use the "Save As" feature of your browser.

Black rot, brown rot, root rot, soft rot - they can strike your orchid plants when conditions are right. Seems as an orchid collection expands and space gets tight, the chance of a rot diseases increases. Rots are diseases that cause decay and death of plant tissues. Affected parts become black or brown. They will look and feel wet and mushy. These rots are often caused by bacteria or fungi. Control of rot depends on changing the growing conditions that allowed it to develop. Attempted cure of infected plants require the sick parts of the plant to be removed and the rest of the plant sprayed with a fungicide (according to directions on the package). Always make cuts with a hot instrument, and then place a covering of fungicide paste on the wound. The hot cutting instrument cauterizes the wound and the fungicide cover prevents secondary infections. Below are some of the more common rots and some suggestions for possible cures.

ORCHID BLACK ROT

Probably the most destructive disease to hit any orchid plant. Cattleyas are most suspectible.

Symptoms:

Usually starts on new leaf or new growth lead. The infection will progress downward through the rhizome until it reaches the roots. Infected leaves, or new growth, will appear purplish/brown or show some brown areas. Other areas become slightly yellow in contrast to the green of the rest of the leaf. Diseased areas become soft. when squeezed, they exude water. Progress of the decay is rapid.

Cure:

Cut off diseased areas of mature plant with a sterile knife. If pseudobulbs are badly infected, cut to rhizome until you come to a place where the tissue is free of disease. Dip plant in fungicide. Dry off before repotting. Black rot is best prevented by not having either plants or surrounding atmosphere too wet. Using a high calcium fertilizer in the Spring, seems to stop black rot in new growth. Dithane M-45 , and Physan 20 provide excellent control on mature plant. Treat seedlings with Anti-Damp Off solution according to package directions.

BROWN ROT

Symptoms:

Often a problem with paphiopedilums. Starts as small, round water spots where water has become lodged in leaves for any length of time. It spreads rapidly, turning leaves a dark brown. happens when plants are hanging in pots over paphiopedilums so that water drips down and settles in leaf axils. high temperature and high humidity are also ideal conditions. Bruised or broken leaves are good places for brown rot to start. Cut bad leaves with sterile shears or scissors. If disease has gone too far, an entire section of plant may have to be cut and destroyed. Dip the plant into a solution of Anti-Damp or Natriphene for about an hour.

BASAL ROT

Symptoms:

This root rot, known as Pellicularia filamentosa , affects seedlings and mature plants. Often happens when potting medium has become severely broken down and/or when plants have poor drainage causing roots to rot. As name implies, it is a brown rotting of the plant tissues. Can also attack rhizomes and pseudobulbs Leaves and pseudobulbs become hollow and shrivel. New growth is not as large as old growth because of root loss. If this is allowed to progress, serious damage can be done, then the plant will have to be discarded. If caught in time, the rotted area can be cut with a sterile knife or scissors, and the plants dipped into a solution of 1 tablespoon of 75% Terraclor in 1 gallon water for 4 or 5 minutes. Tersan and Natriphene are also helpful. Plants should be repotted in clean, sterilized pots with adequate drainage. Only fresh potting material should be used. Plants should be kept from others for several weeks until it is certain that all rot is gone.

SOFT ROT

Symptoms:

Caused by bacteria which enter wounds from improperly sterilized cuts, areas damaged by insects or mechanical damage. Gives off an offensive odor, spreads rapidly, and can be serious if it gets a head start. Cattleyas, phalaenopsis, oncidiums odontoglossums, paphiopedilums and cymbidiums are subject to infection with soft rot. Cut off and destroy all infected parts of the plant. Coat surfaces with Bordeau Mixture (copper sulphate, hydrated lime and water). This mixture can also be obtained commercially in paste or dry form. Disinfect pots and benches with Clorox.

CROWN ROT

Symptoms:

Affects phalaenopsis. Causes collapse and rotting in quick succession of roots, pseudobulbs and leaves. First symptom is likely to be yellowing of leaves. Plants infected should be immediately removed from others. This disease has been known to wipe out a whole section of plants in a day or two. Dip plants into fungicide solution according to directions. Captan, Dithane M-45, andPhysan 20 provide excellent control on mature plant.

RECOMMENDED READING

  • Orchid Pests and Diseases, American Orchid Society
  • Home Orchid Growing, 5th Ed, by Rebecca Northen
  • Encyclopedia of Cultivated Orchids. by Alex D. Hawkes
  • Growing Orchids Book Three. by J. N. Rentoul
  • Dendrobium Orchids of Australia by Walter T. Upton
  • All About Orchids by Charles Marden Fitch
  • The Illustrated Encyclopedia of Orchids, by Alec Pridgeon
  • The Manual of Cultivated Orchid Species, by Bechtel, et al
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