Disease and Disorders

[fred]

I hope this information helps

Unfortunately, along with the pleasure of seeing your orchids come to bloom, there are a few negative aspects to orchid growing such as disorders and disease.
Most orchid sicknesses are preventable by proper growing conditions. We hope you never encounter any of these.


Basal Rot
Basal rot is commonly known as 'Southern Blight'. It is directly
related to watering methods and practices. Either overwatering, or water left standing in the crown of plants combined with cool humid situations can bring on this condition.

On soft and broad leaved orchids there is little warning. Basal rot, as the name suggests, starts at the bottom or the crown of the plant and proceeds upward. Therefore, by the time you notice a problem, it is already too late. If the condition is discovered on a plant with multiple growths, and only a small portion is afflicted, you can attempt to save the plant by cutting away the diseased portion with a sharp knife and treating the wound with sulphur. Keep on the dry side after the "operation" and hope the rot does not spread.

Botrytis
This is a fungal disease which affects primarily the flowers of phalaenopsis,
cattleya, cymbidium and dendrobium. This condition occurs most frequently in cool, moist conditions where there is little air movement. Symptoms are tiny black spots on the petals which soon grow larger and in extreme circumstances are covered with a grey fuzzy mold. If caught early, take measures to increase night time temperatures to no less than 65 degree F and provide maximum air circulation.

Remove and destroy badly infected material such as dead flowers which have fallen to the floor and are covered with mold. Spray flooring with a strong solution of fungicide. This will not reverse the damage already manifest on your bloom, but should dry up the affected areas and halt the further spread of spores.

Fusarium Wilt
Its a disease in itself, but rather a common affliction due to poor culture or
growing conditions. The most often contributing factor is severe shortage of water, especially during the growing season. This is evidenced by extremely shriveled, desiccated leaves. The whole plant is noticeably suffering and appears grey in color. Overwatering can produce the same symptoms once the roots have rotted and can no longer provide moisture to the plant.

Remedy: Pull the plant out of the pot. If there are no live roots, give it a decent
burial because it will not be worth the time and effort spent to attempt a resurrection. If in the early stages however, and if there are still some viable roots present, you can attempt to save it.

Repot immediately in fresh moist orchid seedling mix. Put the newly potted plant in a more subdued light than where it was growing and keep the mix on the moist side, but not wet. Mist once or twice a day to help humidity. You may see no improvement at all until the next growing season when the plant will attempt to put forth new growth along with a new root system.

Pseudomonas Cattleyae
Pseudomonas cattleyae, also known as 'brown wet spot' occurs mostly in phalaenopsis. However, a similar wet bacteria infection can occur on other orchids as well.

Plants develop brownish black, soft areas usually starting on the underside of the leaves and quickly penetrating to the leaf surface. This affliction is a destructive rot which can spread with amazing speed, taking in the entire plant within only a few days. The cause is a combination of cool temperatures, high humidity and inadequate air movement. Prevention is easier than the cure. Keep minimum night temperatures around phalaenopsis at least 60 to 65 degrees F, along with brisk air circulation. Brown wet spot can not develop
under such conditions.

Remedy: If the disease has reached the crown portion of the plant, there is no
cure even if some of the leaves look healthy. On phalaenopsis, if caught early, the affected leaf should be cut off (well below the afflicted area) with a new razorblade or some other sterilized cutting tool. Wet rot on other orchids must be treated by lancing and then cutting and/or scraping out the damaged tissue.

Dust the cut surface with sulphur or a good powdered fungicide. Lacking these, you can use regular mouthwash, applied half strength. Try to rapidly dry off the injury by placing the plant before a fan. Isolate from your regular growing area to prevent any spread on the disease.

Virus
This is the most dreaded orchid disease because it can not be visually identified in its early stages. Orchid virus disease invades and kills leaf cells which condition in turn facilitates secondary bacteria infections. The disease has no preference to type or genus and can spread from plant to plant indiscriminately by insects or cutting implements. In the advanced stage,
orchid leaves will display ugly black rings, circular or diamond shaped spots.

With the exception of the tell-tale black spots on the leaves, some plants appear otherwise normal and continue to produce normal spikes and blossoms. Unfortunately, there is no remedy or cure for orchid virus and the only positive way to know if your plant is infected is through laboratory testing. There are many other causes for black discoloration on orchid leaves and that condition in itself does not necessarily mean that your orchid is infected by virus.


Maintaining consistently clean growing conditions along with common sense cultural practices including optimum temperature and climate, will go a long way towards keeping your orchids healthy and in top condition.

[Cynthia, Prescott, AZ]

Fred, I am of the understanding that Fusarium Wilt is definitely a desease, and a very deadly one at that, and should not be confused with wilting because of loss of roots. Fusarium wilt generally leaves a red lining under the outer layer of tissue along the rhyzome, and excising the bad tissue means cutting until there is no more red visable. I have had a few cases that I suspect was fusarium wilt, with a strong red caste on the leaves, or perhaps a related desease, which was extremely deadly. I have recently arrested the problem in a young plant using Phyton 27, with repeated spraying several days apart.

The comment about it not being worth trying to save plants that are rootless should be read as Fred's opinion, and not one I share at all. I have saved many a plant without roots, and it is well worth while, especially for a favorite plant that is not replaceable.

On the subject of virus, my reading indicates that the only insect that has been proven to transfer virus is aphids, which harbor the virus within their mouth area somewhere, and inject some kind of juices into the plant as part of the process of eating.

[Richard Butt]

Fred,
Recent purchase of an Onc. had black spots on the underside of leaves near the tip. I sprayed with Schultz's "Fungicide Plus"(Myclobutanil and Permethrin are the active ingredents). Do I continue to spray every few days until the spots are gone?
Advise,
Richard