Common Lily Diseases and Pests

Lilies are hardy plants that are relatively easy to grow. But there are a number of diseases and pests that can present challenges to that goal.

Aphids

Aphids are a common pest of many plants and, unfortunately, lilies are no exception. They reproduce rapidly in the spring then the offspring begin to feed on any plant nearby. Their small bodies are visible on the leaves and can be easily washed off with a hose. However, when they reach a certain population density, other measures may be called for.

Insecticidal soaps are one easy, low-impact way to control them. There are commercially available systemics that go a step beyond and not only kill, but help prevent aphids. A systemic is a chemical that is added to the soil. The plant takes it up and when the aphid sucks the sap it ingests the lethal pesticide at the same time. Systemics do not harm the plant.

Aphid control is particularly important since not only can they destroy a single plant, but they may spread viruses. Viruses invade individual cells and the aphid consumes it when it feeds. But some remains on the outer parts of the aphid where it can be implanted onto the next plant the aphid visits.

Lily Beetle

Beetles are another common garden problem and there is one in particular that really likes lilies: the aptly-named Lily Beetle (Lilioceris lilii). A relatively recent immigrant from Europe, it is easy to spot. It has a bright red upper body about 1/4 inch long and a black belly. The larvae are orange. Both the adult and offspring feed on lilies, with the larvae clinging to the underside of leaves.

Brushing them off is usually of limited benefit, since they can crawl right back up again and catching them in a bowl is iffy. They appear to have no natural predators in North America and so chemical control is usually best.

Neem oil is one safe way to control them. It is applied to the plant once per week and kills larvae and repels adults. A systemic chemical called Merit has shown good results, too. It should be applied to the soil in early spring.

Viruses

Viruses kill by invading the cells of plants and co-opting their reproductive mechanism, then bursting the cell wall when they reproduce. This gradually destroys the plant. Evidence of viral invasion shows up as streaking or mottling on leaves, sickly growth, and smaller than normal plants.

The common Cucumber Mosaic Virus is a good example. It doesn’t just invade cucumbers but infects lilies regularly. The leaves then become brittle and distorted.

Controlling or preventing viruses is difficult. Once infected, unless the plant can recover on its own through natural mechanisms, it is best to destroy the plant to prevent spread. Soaking garden tools in bleach is essential to prevent spreading the virus from one plant to the next during gardening.

Fungi

Basal Rot is the most common fungal invader of lilies. It tends to invade the bulb and eventually destroy it, which naturally kills the plant. Botrytis attacks the leaves and stem, which is almost as serious. Both show up as yellowing of leaves and dried stalks and over-watering is the most typical method of encouraging their growth.

Once they attack, an anti-fungal compound is called for. Even then, though, unless stopped early it is often fatal. The best treatment is prevention through proper Lily plant care.

Fortunately, safe, effective, and easy-to-apply controls for nearly all lily diseases and pests exist.

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