I am new to orchids .. just started this March .. I have not dealt directly with them but know them when I see them. I had been to the Orchid Show in NYC and was about to pick a very green healthy(?) plant when I noticed those dreaded little helmets .. I put the plant back down and took another that was not as big or long in leaf (but clean
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I did find this on orchid.org.uk
Scale, there are two types of scale which you are likely to encounter when growing orchids;-
The first one attacks Phaleanopsis in particular, and can migrate to most other soft leaved plants, look on the underside of the leaves for these hard brown limpet like creatures, if you have only one or two, wipe them off with a cloth soaked in methylated spirits, or resort to a systemic insecticide regime as mentioned in the above paragraph, systemic insecticides act by being absorbed into the plant tissue, effectively making the plant poisonous to its attacker, but they should be used with care, do not exceed the stated dosage to avoid damaging the plant.
Boisduval scale (a very fancy name for a real horror), can be very nasty, and primarily has a taste for Cattleya's and their cousins. You may notice flat round scales on the underside of the leaves, which if left unattended will produce a whole shipment of what appears at first to be a white fungus or mealybug, these are the nymphs by the thousand, and they are setting off to desiccate the rest of you collection, the problem we have in the UK is that it is a tropical insect, and many of our pesticides do not treat the problem, one we have found to be of use recently is Leavington's Natures Answer Insecticide and Fungicide combined, this does unfortunately cover the plant in what appears to be white dust, but it is very effective against this type of scale, and several other pests as well, you will probably have to give the plant a good cleaning after a couple of weeks or so for aesthetics.
I believe you have the second .. ick!
They also say this:
Common scale - Dimethoate, Malathion, Insecticidal soap
Boisduval scale- Sulphur and fatty acid mixture
Here is yet another site and info -
Scale Insects on Orchids
Google Boisduval scale and read, read, read
(That's what I do if I don't know)
Good luck!