Answer: Based on your description it might be a fungal infection. Yuccas do best in sunny locations with good air circulation; avoid overhead watering (obviously rain can't be helped.) Do not handle the plant when it is wet from dew or rain. To prevent reinfection, remove the affected foliage and clean up any debris from the ground beneath the plant. Also do a thorough clean up of plant debris next spring and next fall. Consider mulching under it with pebbles or gravel rather than organic material. For a more specific diagnosis, please consult with your local county extension. If a chemical control such as fungicide is needed, they will have the most up to date recommendations on what to use and how/when is best to apply it. Good luck!
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