Greenfly and blackfly aphids are small pear-shaped insects that damage lilies by sucking the plant juices out of them. Usually the first symptom is the appearance of white "fuzz" on flower buds or the tips of new growth. Other symptoms include curling or yellowing leaves and the appearance of a sticky substance called honeydew, which attracts sooty black mold. Aphids don't usually kill plants, but they can spread plant viruses, so it's important to keep their numbers down. Avoid using insecticides because they will destroy beneficial insects, too. Instead, look for mummified skins of aphids, or dead aphids that look bloated, flattened or reddish-brown. Large numbers of these indicate that natural predators, like ladybird beetles and parasitical wasps, or fungal diseases are already reducing the population. If this is so, you may not need to take any action. Aphids can also be controlled by washing them off leaves with a strong spray of water or by pruning infested leaves.
Slugs and Snails
Slugs and snails chew irregular holes in lily leaves and flowers. Since they hide during the day, you may not see them. Look for the silvery mucous trails they make when they move. To control slugs, remove boards, stones and weedy areas where they hide during the day. Use drip irrigation instead of sprinkler irrigation to reduce moist surfaces that these pests prefer. Copper barriers can help protect plants. You can pick slugs and snails off by hand to remove them. Water lilies late in the afternoon to draw snails out, then look for them when it's dark. Dispose of slugs and snails in a pail of soapy water.
Botrytis blight is a fungal infection that causes brown spots to appear on lily leaves. Silver-gray spores on the dead areas may look like dust coming off the plant. In addition, the buds may be deformed. This fungus infects almost every part of the plant, including the leaves, stems, flowers and seeds. Botrytis blight is worse when the weather is wet or humid. Control it by removing infected flower parts and placing them in a paper bag to be burned or thrown out. Avoid overhead watering and misting, and don't crowd plants because good air circulation helps to keep the plants dry. Fungicide sprays help protect flowers from becoming infected.
Bud Drop/Bud Blast
Short days, low lighting or temperatures that are too high can cause bud blast and bud drop. Flower buds may wither and die prior to falling off the stem, or there may not be any noticeable symptoms before the buds just drop. Asiatic lilies do best when the night temperatures are between 50 and 55 degrees Fahrenheit and when daytime temperatures are between 65 and 70 degrees. The maximum temperature should never exceed 85 F. Providing lilies with night interruption lighting, when they're growing with less than 12 to 14 hours of daylight, can help prevent loss of buds.