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BackTo really succeed with growing orchids one may try to create a surrounding that has pretty much the same climate conditions as the natural habitat of the orchid. There are however difficulties in keeping a relative humidity of 80% and 25ºC day- and 17ºC night temperatures, in a common apartment at a latitude as north as Alaska!
But there are advantages with our cold winters. The higher humidity, in the tropics, enhances the growth of fungal- and bacterial contaminants. The rate of decay (rotting) is substantially higher.
If a plant suffers from fungal infections and rot, it has likely been treated wrong some how. It could have been left standing in an environment that was too moist or humid for it or the temperature might have been too high (there can of course be many things influencing infections and rot). The microbial flora is naturally important. If the place isn't to bee nuked once in a while, you can expect contaminants on every area and in the air.
Most of the diseases on plants are caused by bad growing conditions.
Don't expose the orchid to neither of cold nor hot environments..
Always remove dead material (pathogens can start growing).
See to it that the ventilation is good.
That orchids with pseudobulbs produce wrinkled leaves with the new growth
is not a pleasant observation.
The condition is often blamed on irregular watering and feeding. That the plant
has been wet, followed by a somewhat too long period of draught. Thus the plant
has not been able to grow naturally in a continuous way. There are those who
believe that the phenomenon may be due to genetic faults (Rittershausen). However,
that is a theory and so far is nothing more than wild speculations one probably
shouldn't believe too much of (Axelsson, 2004).
Rot is due to infections of microbes that thrive in humid and warm conditions.
An infection should be treated so it doesn't spread to other parts of the plant.
The most efficient treatment is simply to cut away the infected parts, all the
way to fresh, healthy tissue. This should be done with a sterilized knife or
scissor. The wound should be treated with sulphur, activated charcoal, or cinnamon.
Sterilize knives and sissors by soaking them in a sterilizing solution (alcohol, hydrogen peroxide) and/or by burning them off (using an open flame). The instruments can of course be autoclaved or oven baked (150°C during 2-3h).
A good tip on preventing diseases and the spread of bugs is to put all new-bought plants in quarantine. If the plants would show any sign of infections or if they're hosting bugs, they need to be treated before meeting the rest of your collection.
With regular health-check ups of your plants you will surely increase the chance of noticing when something's wrong and thus be able to fight back that 'evil force' threatening your precious plants.
Armored scales are small animals sucking sap and reproducing rapidly. They damage all parts of living plants (from root to bud). There are many types of mealybugs. They have a shield which makes them more difficult killing with chemical biocides. [2].
An armored scale is unpleasant as it poisons the plant cells at the spot where it enters to feed [2]. This leads to a cell death leaving circular spots on the leaves [2].
Aphids, Mealybugs and Mites are three noxious animals that probably need to be treated against when the plant is suffering from an infection. The mites are not visible, other than certain symptoms (differing between species of mites and orchids).
Springtails are small animals that sometimes can be found in the compost of orchids. These things will not hurt the plant, they live on already dead material.
Snails and slugs may cause you misery since they are more than happy to take part of your vegetable buffet. The easiest way, getting rid of these rather large animals, is to pick them away, one and one. They pretty much eat everything green, so you'd better check the roots too.
A questionnaire answered by experienced hobby orchid-growers showed that thin-leafed orchids more often were attacked by insects and bugs. It's more common with infections and 'invasions' during the late summer and autumn than during the rest of the year.
Viral- and less severe bacterial- and fungal-infections may be very hard to diagnose. The symptoms are often similar to results of neglected care of the plants. Clean tools is a requirement when removing hurt and infected parts. To use the correct biocide (if any) is also important. The air circulation is an important factor. Moving air can dry up condensed water from plant parts and can thus prevent many bacterial and fungal contaminants from growing. Viruses are however hard to stop. The whole plant will have to be destroyed in order to solve a viral problem. The tobacco mosaic virus may exist in tobacco. Cigarettes may spread it!
Virus symptoms can mistakenly be taken for bacterial- or fungal infections. Orchids with yellow to black stripes and dots on leaves and pseudobulb or colour-shifts in the flowers, can be seen as suspicious virus attacks. No remedy but to kill the infected plant is available.
Prevention is the way of controlling viral infections. Put new and infected plants in quarantine. Use sterilized tools and wash out pots before re-using them. Viruses are more common abroad. It's fairly difficult to spread infections as the rules of commerce between different countries demands that phytosanity certificates follow any imported plant.
There are several different types of biocide and other chemical care products. What's important is that the chemicals do the job they're supposed to and that the substances are environmentally friendly. Read the lable carefully and follow the instructions.
Traditionally soft soap and alcohol were mixed to a solution (50mL soft soap, 15mL 50-75% ethanol or isopropanol, and 500mL water). Some people use tops dipped in strong alcohol to kill bugs. In most cases, it's bad treating plants with alcohol. Alcohol will quickly kill the plant-cells.
n.b. pressure bottles (gas cans) have a cooling effect when sprayed and may harm the plant being treated.
Solutions of biocides containing paraffin oil works well against aphids, mealybugs and common insects (Bayer, 2004).
Imidacloprid is an active substance found in some kinds of biocide that are taken up by the plant. As the bug starts drinking from the plants sap, it's poisoned. These biocides are often flammable and poisoneous.
Cover the plant with a plastic bag and spray it from below. Seal the bag and let the plant-package rest in a hot place during a few hours or so. The active substances need time to condense on the leaves of the plant and the plant has to be able to absorb 'its medicine'.
Pyretrines and piperonylbutoxide are substances that fight a broad range of insects and pests. Such biocides only work when the insects get in contact with them.
There is a natural extract from an Asian tree (active substance: azadirachtine) which had proven to be very efficient. At the same time it's non-toxic to us animals and doesn't harm your orchids.
Cinnamon can actually be used as a protective and inhibiting substance. Use it on all open wounds on plants and on infected parts.
Sulphur powder is used, in the same way as cinnamon, on open wounds and on infected plant parts. One can also dissolve some sulphur in a bit of liquid soap and mix it up with some water to have an infection-inhibiting spray.
Activated carbon or powder of charcoal is used on wounds etc.
The simplest way of treating a plant is to rinse the compost with water.
Bayer (2004) http://www.bayer.se 2004.11.14
[2a] Sjuth A (2002) Sköldlussläktet Diaspis Del1 Svenska Orkidésällskapet 2003:8.
[2b] Sjuth A (2002) Sköldlussläktet Diaspis Del2 Svenska Orkidésällskapet 2003:9.
[3] Kemikalieinspektionen (2004) www.kemi.se 2004.11.14
[4] Pridgeon A. (1992) The Illustrated Encyclopedia of Orchids Landsowne Publishing Pty Ltd., Australia.
Copyrights © Reserved Markus Axelsson, 2005.
