Answer: wonder if you are describing whiteflies. These are tiny white insects that suck the juices out of plant leaves. They will leave tiny yellow marks, called stippling. If you tap the leaves, the whiteflies will use rise in up a "snow cloud" effect. If that sounds like your problem, Insecticidal soap will do them in, but you have to actually spray the insects. The best time to spray is early in the morning before they become active, or in the evening when they are resting on the leaves.
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