Gadenin日本語Get the appScale insects under the leaf bases
Scale is the signature cymbidium pest and it hides where you do not look. The dry papery sheaths wrapped around the pseudobulbs and the overlapping leaf bases give it a sheltered, dark, humid place to breed, and a heavy infestation can build for a year before anything shows on the visible leaf surfaces. By then the plant is losing vigor, the growths are small, and there is sticky honeydew and sooty black mold over the foliage below.
Look for it deliberately. Peel back one of the papery brown sheaths at the base of an older pseudobulb and inspect with good light. You are looking for small flat oval brown discs pressed to the surface, or clusters of white, slightly fluffy specks which are the males and the crawlers. On the leaves themselves scale sits along the midrib on the underside, leaving a yellow spot on the upper surface where each one feeds.
Treatment is physical first. Strip away every loose dry sheath from the pseudobulbs and bin it, which removes both the insects and their hiding places at a stroke. Scrub the exposed bulbs and both sides of the leaves with a soft brush or cloth and soapy water, then treat with horticultural oil or an insecticidal soap, covering leaf undersides and every crevice. Repeat every seven to ten days for at least three rounds, because the eggs sheltered under the dead females are not touched by the first application.
Isolate an infested plant from the rest of the collection while you work through the cycle. Scale crawlers move between touching leaves, and a bench of orchids pushed together is one continuous plant as far as they are concerned.
The rest of the pest list
The other pests split neatly by season. Summer outdoors brings the chewers and the sap suckers that arrive from the garden; winter indoors brings the ones that thrive in dry warm still air. Knowing which season you are in tells you what to look for first.
| Pest | First sign | Where to look | What to do |
|---|---|---|---|
| Red spider mite | Fine silver stippling and a dull gray cast to the leaves | Leaf undersides, fine webbing in the leaf axils | Raise humidity, hose the foliage, spray oil or soap three times at five day intervals |
| Scale | Sticky leaves and sooty mold | Under dry sheaths and along the leaf midrib underneath | Strip the sheaths, scrub, then oil weekly for three rounds |
| Mealybug | White cottony tufts | Leaf axils, base of new growths, in the mix on roots | Dab with alcohol on a cotton bud, repeat, check the roots at the next repot |
| Aphids | Distorted buds, sticky spike | Tips of developing spikes and unopened buds | Wash off with water or soap spray before the buds open |
| Slugs and snails | Chewed spike tips and holes in buds overnight | Under the pot rim, in the drainage holes, in the mix | Stand pots on feet, check by torchlight after dark, use a barrier or bait |
| Thrips | Silver streaks and brown flecking on petals | Inside open flowers | Remove damaged flowers, spray while in bud, keep weeds away outdoors |
Slugs do the most damage of anything on this list, because a single night's grazing on a soft spike tip removes the whole season's flowers. From the moment spikes appear outdoors, check the pot rim and the drainage holes by torchlight every few nights.
Rots, spots and the difference between them
Bacterial soft rot is the fast one. It appears as a translucent, water-soaked patch, usually at the base of a leaf or on a new growth, which turns brown or black within a day or two and smells foul. It spreads through water splash and standing water in the leaf axils, and it moves quickly in warm still conditions. Cut it out immediately with a sterile blade, taking a margin of clean tissue, keep the plant dry and airy for a week, and stop overhead watering.
Fungal leaf spots are the slow ones: small round or oval brown to black spots, often with a yellow halo, that appear on older leaves and enlarge over weeks. They are unsightly rather than dangerous. Remove the worst leaves, improve air movement, avoid wetting the foliage in the evening, and accept that marks already there will not heal.
Botrytis on the flowers shows as small brown pinprick spots on the petals, spreading in cool damp still air. It is why you never mist a cymbidium in flower. Move the plant somewhere with gentle air movement, keep water off the blooms, and remove spotted flowers so the spores do not build up.
Root and bulb rot is the one that kills. It starts in a pot whose mix has broken down and stayed saturated, the roots go hollow and brown, and the rot travels up into the pseudobulbs, which soften and blacken from the base. Unpot immediately, cut away every soft bulb and dead root, and repot the sound remainder into fresh coarse bark in a smaller pot.
Virus: the one you cannot fix
Cymbidium mosaic virus is common in old collections and there is no treatment. It shows as pale streaks and mottling running lengthwise along the leaves, sometimes developing into sunken black diamond-shaped or streaky necrotic patches, and as color breaking or streaking in the flowers. The plant may keep growing for years while slowly declining, and it stays infectious for the whole of that time.
It spreads on sap, which in practice means on your cutting tools and your hands. This is why the discipline of sterilizing a blade between every single plant matters more with cymbidiums than with almost anything else you grow. Flame the blade, or use a fresh household bleach solution, or use a new disposable razor blade for each plant.
If you suspect virus, isolate the plant, handle it last, and use dedicated tools on it. Test kits are available and inexpensive if you want certainty before making the decision. The honest answer with a confirmed infection in a mixed collection is to destroy the plant rather than keep it, because everything it touches is at risk.
Catching problems early, and keeping a record
Two habits prevent most of this. First, inspect on a fixed rhythm rather than when something looks wrong: once a week in summer, once a fortnight in winter, always turning a leaf over and always looking under one sheath. Nearly every pest on this list is trivial when caught at a dozen individuals and a serious job at a thousand. Second, quarantine every new plant for a month before it joins the others, because most infestations arrive rather than appear.
The moves between outdoors and indoors are the two riskiest moments of the year. Going out in spring exposes clean foliage to garden aphids and slugs. Coming in for winter takes a plant with a few outdoor mites into a warm dry room where they multiply unchecked. Hose the foliage thoroughly, top and underside, and check the sheaths and the pot base before the plant comes back inside.
Write down what you found, where on the plant, and what you sprayed, with the dates. Pest problems on cymbidiums are seasonal and repeat, so a note that says mite appeared six weeks after the plant came indoors last winter tells you exactly when to start looking this year. The same record shows whether three rounds of spray actually cleared an infestation or merely quietened it for a month.