Question
I too have white mould which is sticky and appears on the stems, in the centres and under the leaves.  It appeared about two weeks ago and was just on one orchid and has now spread to the other four.  All three plants have been doing so well for about four years and I think the latest addition has introduced this problem. Can I spray with a rose and ornamental flower spray and also what type of alcohol do you wipe the plants with? can they survive re-potted?

Answer
Hello Heather,

The white mould sounds like it may be boisduval scale.  As you have noticed, they can spread very quickly from plant to plant.  You can use the rose and ornamental spray but make sure the active ingredient is imidaclod, it doesn't take a lot of this to kill the scale so the percentage may seem a little small in it.  Be sure to follow the directions on the container.  It will take 3 to 4 applications over the same number of weeks to get rid of them.  Also, keep a wary eye for their reappearance as they can be very persistent.  The alcohol to use is isopropyl which is available at most pharmacies and stores.  

Not sure what types of orchids you have but most orchids should be repotted in late winter or early spring.  If you have cattleya orchids, wait until you see evidence of new root growth activity before repotting.  Keep all newly repotted orchids in a warm shady location for 2 to 3 weeks then move them back to your normal growing area.  Go easy on the watering during this time to help encourage new root growth.  

Hope this helped.  

Jim Kawasaki
San Jose, Ca.