Diseases and Pests:
Botrytis - is a fungus disease, which affects the leaves of lilies, caused by excessive moisture and warm temperatures. The first signs can be white spots on the leaves. In severe cases the whole leaf and stem can become infected and the whole plant decay and collapse. Injury to plants, like frost or hail will make it easier for Botrytis spores to enter the leaf; spraying is strongly advised very soon after injury. The disease is not carried by the bulb so it will not affect flowering the following year. In early stages of infection, if possible remove noticeable spotted leaves. Spraying is highly advisable, and is only effective when foliage is dry. A copper spray can be
used or natural remedies such as a baking soda mixture (1/4 tsp. per quart of water) sprayed weekly on the foliage during wet periods can also be used. Good air circulation will help prevent a outbreak. Planting lilies some distance apart will also control infection. In the fall clean up and burn dead stems and leaves.
Basal Rot - This fungus invades the bulb through the roots and basal plate. The symptoms on the growing plants are usually premature streaky yellowing of the foliage. The disease can become present in warm moist soils. As a preventive, avoid over-watering during warm summer months and provide good drainage. As for infected bulbs, you can remove the infected scales, dip the bulbs in a fungicide solution of Benlate, which is readily available to home growers.
Blue Mold - Because lilies have a high sugar content, bruising or mechanical injury can cause a penicillin mold to form on the injured part of the bulb. This is harmless to the bulb and can be carefully removed. The bulb can be dusted with a fungicide powder and planted as usual.
Virus Diseases - Lily viruses are transmitted largely by aphids. Visible evidence of virus is; Irregular mottling and flecking of the leaves. Reduction in plant size and height. Distorted, twisted growth. Color-breaking in the flowers and leaves. Brown ring patterns on bulb scales.
A few tips to help control viruses are: Destroy clumps of lilies that show severe infection, insuring that all bulbs and scales are discarded. Remove plants showing infection early in the season. Avoid planting lilies next to other host plants like Tulips or lilium tigrinum (also known as the Tiger Lily). Control aphid infections with the use of insecticides.
Lily Beetle - Long prevalent in Europe, the lily beetle (Lilioceris lilii) has been reported in eastern North America. The larvae and adult beetles feed on the leaves of lilies. The larva is a yellow grub with a dark head, covering itself in dark, slimy excrement. The adult is up to 8 millimeters (0.25 inch) long and bright scarlet with black legs and antennae. Both life stages have voracious appetites and soon devour entire plants. The eggs are laid on the underside of the foliage. The following controls are effective: Spray plants with contact and systemic insecticides; both are effective. Drench soil with a soil insecticide to kill the mature larvae that live just under the soil surface in winter. Also, avoid transporting infested soil to other sites. Catch adult beetles between the fingers and smash them. The lily beetle has only appeared in a few places on this continent, and with care, it should be possible to prevent any lasting infestation.