Answer: I wish there were one way to rid your plants of both pests, but you'll have to treat each problem as it arises. Why not try to trap the adult whiteflies? Use a square of bright yellow cardboard or stiff paper, smear it with petroleum jelly and mount it in or near the foliage of your Hibiscus. The yellow color will attract the whiteflies and they will get stuck on the surface of the trap when they land on it. Remove and replace the trap when it's no longer effective. You can also discourage whiteflies by spraying them with Insecticidal Soap. The spray has some residual effect, but will work best if you can directly spray the insects.
The insects producing webbing are probably spider mites. Spider mites seem to thrive when conditions are dry and dusty and are a real problem for plants during the latter part of the summer. To control the infestation, give your plants a daily shower, carefully rinsing all plant parts, especially the undersides of the leaves. Eventually you'll rinse the insects and their eggs off the plants.
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