Spidermites!

[Moby]

I have a rooftop shadehouse in the city and, before I put my orchids out, I placed two potted plumeria and one Hawaiian Den on the roof. In three days, red (well, the were red-colored) spidermites practically killed every leaf on both plumeria. The Den, just beside them, was untouched as well as a jasmine.

I've noticed these red mites crawling around the rooftop surfaces in previous years and never worried because they never attacked the plumeria or the orchids before. What gives here? Was I just lucky all these years?

If so, what can I do about controlling the mites on the rooftop. It's a large area and spraying won't work for a variety of reasons. Is there a preventive treatment for the orchids I can apply before I take them to the roof?

Lastly, in my research I read that the spider mite that mostly attacks orchids is the two-spotted mite. Mine are flourescent red/orange and very visible to the eye. They move very quickly too. I noticed that they are prevalent on the roof every spring and seem to disappear as the season goes on.

Any advice by you arachnid experts would be greatly appreciated!