Answer: White flies are extremely difficult to control and once they take up residence in a garden, they're usually there for a long, long time. They're more of an annoyance than anything else. Scale insects such the fluids from plant tissues and excrete a sticky substance. This is what is causing the sooty mold on the leaf surfaces. Once you rid your plant of scales, the sooty mold will weather away. Neem oil should suffocate scales but repeat applications may be necessary to get all of the pests. Be sure to apply in amounts and with the frequency suggested on the product label. You can safely prune your gardenia back by about one-third without causing it too much stress. Prune should remove some of the affected leaves and stems, as well as encouraging healthy new growth. I think with regular attention you can help your plant overcome its problems without doing anything drastic - like cutting it down. Best wishes with your plant!
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