I have noticed in the last couple of days what look like red spider mites in my garden. They are closest to my pieris (mountain andromeda) and near my roses and rhodes as well. I looked them up online, but mostly I got descriptions. Could they be the reason that sometimes the leaves on my pieris turn brown and die? Also, what should I use to get rid of them if they are indeed a problem? (there are an awful lot of them) Thanks!