Hi Al
Too much water. If you've got a mulch, once or twice a week tops. Try not to get the leaves wet. It could be a fungus you're growin. With all this rain I haven't watered once this summer.

Joe in NJ
Exit 27

Thanks Joe... I hope this will be ok for the other plants I have in the vicinity too. I'll be sure to water them 2 times a week because of the extreme sun/heat we've been having...

-Al

Hi Al,
Watering in the morning would be best to give them time to dry off. The bulbs themselves don't like being in soil saturated with water for very long. Also if the leaves are constantly wet, Botrytis will occur which is a fungus. The leaves closest to the ground may be turning yellow brown for you. No matter what, there's an excellent chance your lilies will be back next year even if the whole plant turns brown from Botrytis. If there is antifungal stuff at the Home Depot, you could try that. However, what's currently brown will stay brown. Watering your annuals everyday is fine but for the lilies try a different schedule.
Best,

Joe