'FAQ:2003:19 - Lily Bulb' (Lilium)
"Dead-end" corners, thick stands of trees, or low areas, where air lies stagnant, can promote a fungal disease called Botrytis Blight. This is characterized by brown spots on the leaves and/or flower buds. In advance cases, all the lower leaves will rapidly turn brown and die. The bulb itself is not damaged, but the sudden loss of leaves will reduce the number of flowers next year.
Fungal difficulties can arise in any garden when the weather is cold and damp during spring or fall or during hot and humid weather during summer. Providing good air circulation and cleanup of old lily stems in the winter are the best defenses against Botrytis. If you spray roses for Blackspot or Powdery Mildew, spray your lilies at the same time.
Organic gardeners: In addition to reducing humid conditions, try a baking soda mixture (1/4 teaspoon, per quart of water) sprayed weekly on the foliage during wet/cold Spring and Autumn days. Reapply after heavy rain.