Question
Hi Wayne King,

Today I saw white scale on cattleya leaves.  I'm wondering what cause them to appear on cattleya. Is is too hot or wet?

How to control them in future & get rid of them now?

Thanks,
Nwe Lay

Answer
Nwe, actually, cattleya and other thick leaved orchids are the favorite hosts for scale.  However, when you described the scale as white, I wonder if it is scale or mealy.  Scale tends to be brown, gray, or semi-transparent.  They are difficult to get rid of, especially if they are well established on the plant.  A good start to eliminate them is to remove all visible adults and crawlers by rubbing them with 70% rubbing alcohol using an alcohol soaked cloth, q-tip or cotton ball. Since this will leave the majority in the form of eggs and crawlers in the potting material and hidden under sheaths, you will need to use a systemic insecticide which will penetrate into the plant tissues and kill any sucking insects over thee next month.  Unfortunately, constant vigilance is needed to spot any future insects and destroy them in a similar fashion.  In the adult stage (ie scale stage) contact insecticides are ineffective so they must be removed using the alcohol rub. Both scale and mealy can spread rapidly from plant to plant so be sure to isolate any infected plant while you treat it.  You might consider a drench in the systemic insecticide followed by repotting in a fresh pot and potting mix.