Scale Insects on Orchids
Now that our lovely warm summer is over and our orchids must get ready for winter, there is one special area of care-giving that must not be neglected - scale insects love to settle on orchids, especially during warm and dry weather. This holds true for both (commonly found) types:
The Soft Scale “Bois du Val”, which is greyish-white, can be mistaken for mealy bugs and will be found on stems, buds, canes, pseudobulbs, the undersides of leaves and even on the roots near the surface of the potting mix. A heavy infestation can have 5mm thick coatings of these greasy bugs – all in one continuous mass.
The Hard Scale damages plants in the same way by sucking the juice from their tissue. Mature hard scale looks like shiny brown half globes, generally about 2 – 3 mm across and will be found mostly on the underside of leaves as well as in all the tight spaces, where you cannot get at them! The young scale hatch from dust-like eggs and mature quickly. They are almost invisible even when they have reached adult size (get a magnifying glass if you need to look at them). Before the hard coating develops they can look like flat green or white spots on the leaves and don’t move much, if at all.
We know that pests of any description are part of nature and we cannot get rid of them out-doors. We can however, try to get rid of them when they sit on our orchids. How? …with patience, perseverance and (sometimes) poison.
If you have many infested plants (over ten), you will be better off to use poison – ask your garden centre for advice. Please do read all instructions and cautions on the labels. You only want to kill the pests, not your family or your pets. There are a few poisons that are not advised for use on orchids – again, read the labels, even before buying. If you have to use any poison on budded or flowering plants, the flowers will show damage that should not appear on the next year’s flowers. I recommend that, if you must use any poison, place the affected plant(s) in a large plastic garbage bag, apply the poison, tie the bag shut, keep it in a safe, protected place for 24 hours and then let it air out before taking it out of the bag. You must repeat this treatment two more times, about a week to 10 days apart.
Sometimes, rubbing alcohol may be used to wipe the bugs off – this is a very harsh treatment and if done too often, the orchids will die.
Most times, there will only be a few plants that may have these nasty scales. In this case, don’t do the poison treatments. Take the plant to the sink and carefully wash the whole plant, every square centimetre of leaves, stems, canes etc. with warm water into which you have whipped some grated soap (real soap, like ‘Sunlight’). Keep the plant by the sink so that you can watch it. You must do this every other day for about one month. If you need glasses to read, I would recommend that you put on your glasses when you work with the orchids. You have to be vigilant and consistent. I had found some scale on some orchids and after only two weeks of this treatment, there are a lot fewer insects – hopefully, after a month, they will be all gone. Then it is a matter of observing – as usual. It is a good idea to keep sick and convalescing plants segregated for a month after any treatment.
Ingrid Schmidt-Ostrander - Canadian Orchid Congress