Orchid Diseases and Orchid Pests
Orchid diseases are, in general, uncommon. Good healthy orchid plants which have been cultivated under well-aired conditions, are rarely attacked. An occasional orchid plant may be subject to an attack of black rot disease. Diseased parts of the plants however, can be carefully removed by cutting them away and applying powdered sulphur directly onto the cut surface. If such rots are caught in time, they can be controlled, but particularly badly infected orchid plants are best to be destroyed. Virus disease however, is the one exception. Virus disease appears, particularly in cymbidiums, as ringed areas or yellowish streaks which then eventually turn a dark or blackish colour. New orchid propagation techniques will ensure that only healthy orchid plants are distributed, while any infected plants should always be burnt. You can reduce the risk of the spread of the virus, by controlling red spider mites and other sucking insects such as greenfly.
The main orchid pests are scale insects, mealy bugs, red spider mites and thrips.
Scale insects, as the name implies, appear as small, greenish or brownish scales on the stems and leaves, especially of cattleyas, where, in bad infestations, they actually get behind the bulb sheaths themselves. Control of such orchid pests has to be done by spongeing or spraying with an appropriate insecticide.
Mealy bugs are small insects covered with a grey meal and can cause considerable damage if allowed to remain untreated. Like scale insects they also find their way under leaf sheaths and bracts. Small pockets of these insects can be checked by applying a mixture of methylated spirits and nicotine, with a small artist’s paintbrush.
Red spider mites are minute, hardly visible without a magnifying glass, ranging from greenish to red in colour and only found on the undersides of the orchid plant’s leaves; where they cause, in bad infestations, a dry silvered appearance on the leaf surface. They are sucking creatures that live on the plant sap. They can be considered to be the worst enemy of the orchid grower as they can transmit viral disease in their transfer from one orchid plant to another plant. It is vital that alternation of control sprays is utilized, as resistance to a single spray is soon built up, having little or no effect. Malathion, derris and Chlorocide sprays can be used in rotation.
Thrip is a minute insect also, and its presence is detected by small round, punctured and discoloured areas on the softer leaves and on thethemselves.
The best approach to orchid pests is to ensure regular spraying as a preventive measure. Always follow the manufacturer’s instructions, as some chemicals can be dangerous if due care is not taken.
New orchid plants should always be carefully inspected, especially those plants that are imported.
Slugs and snails particularly like fresh young orchid growths as well as their roots and flowers, and a good control can be effected with Slugit used either as a spray or as pellets and these could be placed on the benches in the orchid house, around and between the pots.