Is Merit still sold??? I thought that was one that was deemed "dangerous" and no longer available... I wouldn't use anything quite that lethal. I use Bayer's Tree & Shrub, available at HD or Lowes. Seems to work fine. 1 oz. per gallon of water. Should take care of the problem.

Denise in Omaha

Scale are easy enough to kill when they are small and still in the crawling phase. Insecticidal soap, neem oil, etc all work well. The adult phase is harder to kill and if you leave the adults on the plant they will produce many eggs under the scale and the process will repeat it's self.
Like Denise said there is no reason to risk personal injury by using such powerful pesticides when something far less toxic will do. Start with a dish soap and water plus alcohol spray and repeat it every week for a few weeks and see if that works. If you need to use something more powerful Bayer's product works well but keep the plants away from pollinating insects like bees and take personal precautions as well. The active ingredient in Bayer's insecticide is linked to the death of millions of bees across the world and several countries have banned it's use so it helps to educate yourself about it so that you can be safe. Do a search for the active ingredient Imidacloprid plus bees and see what comes up, startling and something that more gardeners need to be aware of.

Mike

Appreciate all! And very much appreciate the caution - truly. I don't think folks think far enough in advance anymore and willy nilly do things. Consequences are devastating so it helps to be reminded.

While I don't have any problems now on my Hoyas (thank you thank you thank you for the little things!). I do have a few orchids with scale and mealys and one being around the other know that it is a matter of time. I use the Neem oil plus the insecticidal soap for individual plants (as well as the alchohol swabbings) but if I lose the 'individual' battle, I'll break out the arsenal....which I hope doesn't happen.

Oh, and appreciate! You've answered my question.