Gadenin日本語Get the appScale insects: the one to look for first
Scale is the defining cattleya pest. Boisduval scale in particular lives under the dry papery sheaths that wrap each pseudobulb, where it is completely hidden from view, and by the time you notice pale mottling on the leaves or a dusting of white on the outside of the bulbs the colony has been building for months. Peel back a bulb sheath on any cattleya you suspect and look: you are looking for flat brown limpet-like scales and a scurf of white fluff, which is the males.
Deal with it by stripping every dry sheath off every pseudobulb, which takes the shelter away permanently and is worth doing routinely on any newly acquired plant. Then scrub the exposed bulbs, leaf undersides and the rhizome with a soft toothbrush and soapy water, and follow up with horticultural oil or an insecticidal soap. Cover the whole plant including the underside of every leaf and the crevices at the leaf joint.
One treatment never clears scale, because the eggs and crawlers survive it. Repeat at seven to ten day intervals for at least three or four rounds, and check again a month later. Isolate the plant from your others while you do it, since crawlers walk between touching leaves.
| Problem | What you see | First response |
|---|---|---|
| Boisduval scale | Brown limpets and white fluff under bulb sheaths, mottled leaves | Strip sheaths, scrub, oil spray, repeat weekly for a month |
| Mealybug | White cottony blobs in leaf joints and among roots | Dab with alcohol on a cotton bud, then soap or oil spray |
| Spider mite | Fine silver stippling and dull silvered leaf undersides | Wash foliage, raise humidity and air movement, oil spray |
| Thrips | Streaked, distorted or brown-speckled buds and flowers | Remove affected buds, treat, keep new buds covered from outdoors |
| Slugs and snails | Chewed new root tips and holes eaten in buds overnight | Raise pots off the ground, hunt after dark, use bait or a barrier |
| Black rot | Spreading black soft patch on leaf or new growth, foul smell | Cut well back into clean tissue at once, dry out, improve airflow |
| Virus | Permanent streaks, rings or color breaks in leaves and flowers | No cure, discard the plant, sterilize tools |
Black rot and the wet leaf joint
Black rot is the fastest killer of a cattleya. It begins as a soft dark patch, usually on a new growth or at the point where a leaf joins its bulb, spreads visibly within a day or two, and smells sour. Water sitting overnight in a leaf axil or in the crown of an expanding new growth is what lets it start, so it is very much a disease of overhead watering, misting and still air.
Act immediately. Cut the affected leaf or growth off well below the visible damage, into clean firm green or white tissue, with a sterile blade, and burn or bin the piece. If the rot has run into the rhizome, cut the rhizome and sacrifice the section, because a rot that reaches the rhizome takes the whole plant. Dust the cut surfaces with cinnamon or a copper or systemic fungicide.
Then change the conditions that caused it. Water the mix rather than the plant, water in the morning so anything splashed dries by nightfall, stop misting, and get air moving with a fan. Cattleyas in a bright airy position with dry foliage overnight almost never get black rot, whatever else they are exposed to.
If you find a wet, sour, collapsing mess in the pot rather than on the leaves, the problem is root rot from a broken-down mix rather than a leaf disease. Tip the plant out, cut every dead root away, repot into fresh coarse bark in a smaller pot, and water sparingly until new white root tips appear.
Leaf spots, and the ones that mean nothing
Not every mark on a cattleya leaf is a disease. Dry, sharply edged cream or white patches on the top surface are sunburn, and once scarred they stay. Small hard sunken black dots that never spread are usually old physical damage or a fungal spot that the plant has already walled off. Neither needs treatment; watch them for a fortnight and if they have not grown, ignore them.
Marks that spread are the ones to act on. A brown or black spot that widens week by week, has a yellow halo, or has a soft edge is an active fungal or bacterial infection. Cut the affected leaf off at the base, improve air movement, keep the foliage dry, and treat with a suitable fungicide if it continues on other leaves.
Yellowing of the oldest, leafless bulbs and the eventual drop of the oldest leaf is normal ageing. Cattleya leaves live three to five years and then go. What is not normal is yellowing of the newest growth, which points to root loss, and that means tipping the plant out and looking rather than treating the leaf.
Virus: the one you cannot fix
Orchid viruses show as permanent streaks, rings, mosaics or color breaks in the leaves and, most tellingly, in the flowers, where a solid color breaks into blotches or the petals show necrotic streaks. There is no treatment. An infected plant remains a source of infection for everything else you grow and should be discarded rather than nursed along.
Virus spreads in sap on cutting tools and hands, which is why sterilizing blades between plants matters more with cattleyas than with most houseplants. Use single-use razor blades or flame a knife red hot between plants, and wash your hands after handling any plant you are unsure about. Sap on pruners used to cut a flower stem from one plant and then another is the classic route.
If you suspect virus but are not certain, isolate the plant, handle it last, and never take a division from it. Test kits are available if you have a collection worth protecting.
A monthly check, and what to log
Once a month, pick each plant up and look at it properly for two minutes: peel a bulb sheath, turn the leaves over, look into the leaf joints, and check the rhizome and the surface of the mix. That single habit catches almost everything at the stage where a soap spray or a scrub still works, rather than at the stage where the plant is beyond saving.
Quarantine every new plant for a month away from the rest, and strip its bulb sheaths on arrival. Most collection-wide scale outbreaks arrive on a single new plant and are invisible for the first several weeks.
Keep a short log: the date you first saw a pest, which plant it was on, what you sprayed and when, and the date you stopped seeing it. Scale in particular comes back on a delay, so the record of when you last treated is what tells you whether the plant is genuinely clean or simply between generations.