Answer: The foliage should stay a healthy green until late summer or fall when it naturally yellows. It may be a fungal infection of some kind, given the humid summer weather we usually have, or perhaps mold growing where aphids have caused damage. I would suggest you consult with your local county extension to obtain a definite diagnosis of the problem and based on knowing that, determine how to proceed. If it is something that requires spraying, they will have the most up to date information on what to use and how/when is best to apply it. Good luck with your lilies!
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