Orchid Pests and Diseases

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Though no grower readily wants to admit it, every grower has, at one point or another, encountered attacks by insect pests on their orchid plants. If they haven't yet, they will. It's part of the process. Orchid growing brings with it a set of conditions pests seem to thrive in, and depending on what part of the country you're in, the little nasties that plague you may vary.

We've encountered scale, sowbugs, mealybugs, slugs, aphids, ants, and spider mites.

White Scale: A few lumps such as these can easily be sprayed with Ultra Fine and water and brushed off with an old toothbrush.

Dealing with these things remains a constant challenge, but here are some tips that will help.

Your first line of defense against insect pests is your own vigilance. Unless you're growing your orchids under sterile conditions, the bugs will come, so stay alert. Keep your growing area clean and free of debris. Dead leaves and flowers littering the floor or benches, wet cardboard boxes in the corner, old bark laying around all give insects places to hide and grow. If you're fond of Cattleyas (and we are), keep their sheaths peeled from the pseudobulbs. Scale thrives in the dark and the damp, and Cattleya sheaths offer scale insects a perfect hiding place, even protecting them from some pesticides.


If you do find that your plants have been overrun by some type of orchid pest, deal with it right then. Don't wait. Insects multiply at an alarming rate and, before you know it, a bump of scale here and there will turn into a full-blow infestation literally covering the undersides of your orchid's leaves in a white, powdery mass.

Try to use a natural type of pesticide first before moving on to the hard-core stuff. We have very good success with Ultra-Fine Pesticidal Oil mixed at 3 tablespoons per gallon of water and sprayed on at the first sign of trouble. You can then use an old, soft toothbrush to clean the pests away. Other growers have reported success with Hot Pepper Wax, and lately, Neem Oil. If you decide to go in for the hard-core stuff, any type of pesticide formulated for Ornamentals will work. Make sure you follow the mixing instructions for Orchids or Ornamentals, as too strong a dilution can seriously damage your orchid plant. Sowbugs, slugs, and other pests that live in the potting medium can be eradicated by watering the plant with a Malathion solution mixed with water, again, as for Ornamentals.



Of all the diseases that can infect orchids, virus infections are the most dreaded as there is virtually no cure. Symptoms include circular or diamond-shaped brown spots and blotches on the leaves and color streaking in flowers. However: this does not mean that every orchid with brown-spotted leaves is virused. Brown spots can occur because of sunburn, the sudden onset of bright light after a dark winter, or a fungus infection. Since many orchids retain their leaves for several years, foliage is bound to develop markings and spots as the leaf ages. If you do suspect a virus, you may pay to have your plant tested at one of the many labs set up for this purpose. Check the "LINKS" page for more information. The best "cure" for a viral infection is prevention: keep your growing area clean, and always used sterilized implements if you're going to be cutting into your plant. This includes cutting off old flower spikes that haven't completely browned out yet.

Brown rot is a bacterial infection that causes wet, brown spots to appear on leaves and pseudobulbs. It can be caused by temperatures that are too low and humidity that is too high, or by a slug that has begun to graze. These infections can spread quickly so they must be dealt with as soon as they're noticed. Using a sharp, sterilized knife or single-edged razor blade, cut away the affected area and dust the wound with either sulphur powder, a solution of Physan and water, or some other antibacterial agent designed for use on Ornamentals. If allowed to spread, these infections can kill your plant in a matter of days.

Black rot and crown rot are fungal infections which usually result from overwatering or watering in the evening so that water is left standing in the crown of the plant. Spray the plant with an appropriate fungicide for use with Ornamentals. Unfortunately, if crown rot infects a Phalaenopsis, the plant, with no other active area of growth except the crown, will die. All fungal infections can be avoided by proper culture: do not overwater, water only in the mornings so that your plant has a chance to dry off before nightfall, and provide plenty of air circulation around your plants. If you notice a puddle of water standing in the crown or active growing center of your orchid, soak it up with a paper towel.

This list is by no means exhaustive. Much research has been done in the area of orchid disease; for further information, consult the "LINKS" page.

Scale Infestation: Peeling back the sheath on this Cattleya's pseudobulb revealed a powdery mass of scale, feeding beneath. Unless eradicated promptly, infestations like this can quickly damage and kill an orchid.
Brown Spot on an Oncidium: Most likely a fungal infection, these brown spots often appear on older Oncidium leaves that have been grown in high humidity over the winter then exposed to bright, summer light.
Leaf Die-back: Possible causes on young leaves include recent overwatering, conditions that are cold and damp, or sudden exposure to bright sunlight. Cutting off the brown end with a sterilized razor blade often halts the spread. On older leaves, this may just be the natural aging process.
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