Bugs on Dahlias

My dahlias are about a foot tall, and about to bloom. I noticed tonight as I was watering that they seem to be covered with tiny black dots. They washed off with a strong stream of water, but what I need to know will they come back, what are they, and what can I do about them. They seem to be doing well other than these mite thingys.
Thanks Nancy Boston MA Zone 6a
Cham http://groups.yahoo.com/group/east-coast-wx /
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