THE MOST COMMON
PATHOGEN & PARASITES |
DESCRIPTION &
SYMPTOMS |
TREATMENT |
SPIDER MITES
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Spider mites (Tetranychus urticae: two-spotted tiny arthropods with four pairs of legs) received their name because of the silk webbing that they build. They are barely visible to the naked eye. In a light invasion, small yellowish dots followed by pale patches appear on upper leaf surfaces but in a heavy infestation, the leaves may turn completely yellow or bronze and you will see fine whitish webbing under the leaves. |
The easiest method for keeping mites under control is to regularly spray the plants with water. The most popular home remedy is to spray plants with a mixture of 30% water, 70% rubbing (isopropyl) alcohol and a few drops of dish detergent. The alcohol dissolves the insect’s waxy covering, and is a good tool to reach the pests hidden down in the sheaths and leaf crevices. |
MEALYBUGS
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Mealybugs (Pseudococcus sp.: soft-bodied, sap-sucking insects) are quite common pests and look like a cottony mass clearly visible to the naked eye. They are hard to eradicate because of their defensive waxy-whitish substance outer covering. Ants transport them and you cannot get rid of them until you get rid of ants. |
Mealybugs arise when too much humidity in a low light situation is present. To kill them, on an individual plant, a q-tip dipped in rubbing alcohol works well. You could also use a spray filled with 70% rubbing alcohol, and after a few minutes, mist plants with plain water to wash away both the alcohol and bugs. Look at plants every day and repeat if needed. Also you should control ants. |
APHIDS
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Aphids or Plant lice (Macrosiphum Lutem: a pear-shaped ovoid with six legs) are identifiable by the presence of a pair of short tubes in the last portion of their abdomen. These insects can attack orchids year-around, but are mostly autumn and winter problems. Their constant pumping of sap causes buds produce deformed leaves and leaves to become discoloured and curled. Aphids also secrete honeydew, which is attractive to ants, flies and bees. A black fungus (sooty mould) grows on the honeydew as well. |
The easiest method for keeping aphids, scales, mites and mealybugs under control is to regularly spray the plants with water. The most popular home remedy is to spray plants with a mixture of 30% water, 70% rubbing (isopropyl) alcohol and a few drops of dish detergent. The alcohol dissolves the insect’s waxy covering, and is a good tool to reach the pests hidden down in the sheaths and leaf crevices. |
SCALES
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Scales can be divided into soft and hard scales. A dome-shaped shell shelters hard female scales (Boisduval scale, Diaspis boisduvalii, and other: small, round insects from 1 to 5 mm long) and soft scales (Coccus hesperidum) produce honeydew. A serious invasion can cause the leaves to wilt, dry out and drop off. Young plants are more susceptible than mature ones. Cattleyas are highly vulnerable to hard scales. |
Isolate infested plants. Start by pruning dead or seriously infested branches. Remove all visible scale insects (dead or alive: they may be sheltering hundreds of eggs). Leaves and young branches: rub with a cotton ball soaked with a solution of 70% rubbing alcohol and 30% of soapy water. |
SLUGS & SNAILS
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The warm, humid conditions encourage slugs and snails. Although these pests often go unnoticed since they feed at night, burnished trails on the leaves indicate their presence. They can severely damage orchid buds and flowers. |
By dusting the place generously with Diatomaceous earth, they will gone. It works very well. Metaldehyde is the traditional method of control, but liquid and pellet-form slug killers are also currently in use. Their damage can be lessened by not setting plants directly on the ground when putting orchids outside for the summer. |
VIRUS
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A number of viruses attack orchids, some of which produce leaf symptoms. The three most common viruses that affect orchids are ORSV (Odontoglosum Ringspot), TMV (Tobacco Mosaic), and CYMMV (Cymbidium Mosaic). They weaken the plant by disturbing normal growth and causing deformity of plant structures. Symptoms include circular or diamond-shaped brown spots and blotches on the leaves and color streaking in flowers. |
Virus infections are the most dreaded as there is virtually no cure. Virus can be mechanically transmitted from an infected plant to a non-infected plant by any tool that comes into contact with the plant’s sap. Always sanitize (sterilize) any implements you use on your orchids, before and between each orchid you work with. There is no practical cure, destroy plant. |
FUNGUS & BACTERIAS
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Fungus and bacterial infections are usually characterized by black or brown spots that can appear on any part of the plant. Brown rot is most probably a bacterial infection that causes wet, brown spots to appear on leaves and pseudobulbs. Crown rot is a fungal infections which usually result from overwatering or watering in the evening. Brown spots can also occur because of sunburn. |
Good air movement is the best tool to prevent against fungal and bacterial infections. Do not overwatering or watering in the evenings, water only in the mornings so that your plant has a chance to dry off before nightfall. The most efficient method to treat bacterial and fungal disease is the regular use of a systemic agent (Phyton 27, Physan 20, R-D-20, etc). |
