Answer: Based on your description I am not certain whether this would be a disease such as botrytis fungus, or a pest, possibly the stalk borer. I would suggest you consult with your local county extension and see if they can give you a more specific diagnosis. Based on knowing that, they can suggest a control. If a chemical control is needed, they will have the most up to date information on what to use in a home garden and how/when is best to use it.
In the meantime, avoid wetting the foliage if you water the lilies, and clean up and remove any affected leaves and stems. Dispose of them in the trash to limit reinfection. This fall, after frost kills the stems, do a thorough clean up of all the spent lily stems for the same reason.
You might also find the following web page helpful in trying to identify the problem. You may need to cut and paste the complete url into your browser to make it work correctly.
Good luck with your Stargazers!
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