As I recall, the chemicals that kill spider mites are very expensive. On the plus side, I've heard spraying them with a hose can wash them away.

thank you intris

Cedric, do you have spider mites on your roses now? If so, that would be somewhat unusual. It is more common to find them after a spate of warm/hot and dry weather. Intris is right, however: they can be dislodged with a concerted spray from the hose.
As you pointed out, spider mites hang out on the underside of the leaves. For the hose spray to be effective, you therefore must be prepared to spray up from the bottom of your roses. This usually means that the hose wielder gets wetter than he or she might have intended. And since you never get all of them on the first attempt, repeat hosings will be necessary. I would spray every day or two--you don't want to give the next generation a chance to reproduce.

Kay

You don't say where you are or what the growing conditions are. If the roses are inside, or in a greenhouse, or under an eave, mite problems are routine in these conditions. Use of certain insecticides (Merit, Sevin) can also cause outbreaks.

Follow Kay's advice above. You will need a spray wand with a bent neck and the ability to produce a high-pressure, cone-shaped spray.

The two-spotted mite is the usual culprit. If other species are present, these are beneficials that will help to control the TSM.

This post was edited by michaelg on Thu, Mar 14, 13 at 16:30

Do the water spray thing every day for a while, then periodically in the future to prevent re-occurrence.

Using insecticides encourages a population explosion of spider mites since the insecticides kill off predators of the mites, so avoid insecticides as much as you can.

thank you all on your suggestions, it really a lot of help !

A long water wand with a 2" spray head works OK for spider mite blasting. Those fancier wands with a 5-in-1 spray head works well too. Blast 'em every other day for a week, then follow up once a a week.

Spider mite season may be changing, especially in areas that did not have a cold winter. The last two winters here in lower SC have been very mild, with only a couple of light frosts. I found spider mites on our outdoor roses all through both winter. No rest for a rose gardener!