Prevention is always better than cure. It is vital, particularly if you have a large number of plants to check them over at least weekly for any problems. If dealt with at an early stage they can often be eradicated.
Most diseases arise from incorrect cultivation. If the cultivation guidelines covered in this section are applied then health problems will be minimised. Some orchids are more prone to disease than others.
Fungal & Bacterial
Leaf spotting is the most common complaint especially on plants with large flat leaves such as Lycastes, Zygopetalums and Brassias. If it is caused by a fungal infection it is typified by many large spots appearing over a short time. The best remedy is to remove and destroy the infected leaves otherwise resort to systemic fungicides.
If wet and mushy rot appears for example on old pseudobulbs or at the base of new ones, the cause is frequently bacterial or fungal. The infected area should be cut out back into the healthy growth and the wound dusted with cinnamon powder (as used in cooking) which is an effective non-toxic anti-bacterial agent.
Virus infections stir fear into the hearts of orchid growers. Virus infections cannot be cured and the only solution is to destroy the plant to prevent potential spread. Viruses often manifest as yellow rings, flecking, stripes, mosaics or diamond-shaped patterns on leaves which will turn black over time. It can also show itself as colour breaks on flowers or distorted growth. However many infected plants remain healthy and symptomless. Viruses are mostly spread through sap to sap contact. Cutting tools must always be sterilised; compost and pots should not be exchanged between plants and sap sucking insects eliminated. Taking these precautions will prevent virus infection from spreading in your collection even if a rogue plant has been introduced.
Insects such as aphids like to feed on new growth and can safely be killed and washed off using diluted washing-up liquid sprayed on under pressure. Mealy bugs appear as white cotton like spots and scale insects as tiny brown blisters both are best picked off and the plants thoroughly washed and monitored for recurrence. You have to be persistent with these pests but eventually their numbers will dwindle and disappear. Red spider and False-spider mites can be problematic particularly in warm dry conditions. They cause as a very fine silver-white spotting particularly on lower leave surfaces where they have sucked out the sap. Fortnightly washing of leaves with washing-up detergent containing Neem oil diluted in water will overcome these pests.
For more detailed information on orchid health issues we advise you refer to the American Orchid Society Website.
Did you know?
Dusting orchid wounds with ordinary culinary cinnamon powder is an excellent non-toxic way of preventing infection of the plant.