Whiteflies
Suspect whitef1ies when you start seeing small (1/12"), pure white "moths" that are mostly resting on the plant leaves. When disturbed, all rush out in the air, hesitate a while, then fly back into the foliage. Looking closer, the plants might appear shiny with honeydew. With a magnifier, small clear- white "scales" (the pupa) are seen on the lower, underneath sides of the plants. All stages suck on plant juices, and heavily infested plants will yellow and grow poorly.
There are at least 2 whitefly species now causing distress for gardeners, greenhouse whitefly and sweet-potato whitefly. What finally kills plants off with a heavy whitefly infestation isn't usually whiteflies themselves, but a black sooty mold that grows on accumulated honeydew. By the time plants get to this stage, there'll be clouds of whiteflies, and no mistaking this pest. If you're at that point, rinse the shiny coating off the plants with a strong water or soapy' water spray, so the mold can't grow on it.