How to Control Red Lily Leaf Beetles
The red lily leaf beetle (Lilioceris lilii) is a destructive pest that feeds almost exclusively on true lilies (Lilium spp.), including Asiatic and Oriental lilies as well as Orienpets and species lilies. Most fritillarias are also susceptible to lily leaf beetles.
First discovered in eastern Canada about 50 years ago, this non-native species has gradually infiltrated most of New England and central and western Canada. In 2012 it began appearing in Washington and Oregon as well. If this pest is active in your region, your lilies are at risk. Here are some ways to protect them.
How to Identify the Lily Leaf Beetle and Its Damage
The lily leaf beetle is about ¼” long and bright, scarlet red. Though easy to see, they are fast and difficult to catch. If they sense you approaching, they immediately drop to the ground on their backs and quickly vanish into the soil.
There is one generation of these beetles per year. Adults overwinter in the soil and emerge in April and May to begin feeding and laying eggs. Each female can lay up to 450 eggs over a period of 3 to 4 weeks. The tiny, orange-brown eggs are laid in rows on the underside of lily leaves and the larvae begin hatching one to two weeks later.
Lily leaf beetle larvae are soft and slug-like. They’re not pretty, but it gets worse. To protect themselves, they carry their excrement on their backs (shown below). It’s an ingenious and super disgusting, yet effective way to hide.
The larvae are voracious eaters and can feed for 3 to 4 weeks before moving down into the soil to pupate. About a month later they emerge as adult beetles and continue feeding before they return to the soil for the winter.
How to Protect Your Lilies from Lily Leaf Beetles
Most plants can generate new growth if their foliage gets eaten, but that’s not the case with lilies. If lily leaf beetles eat the leaves, that’s it for the season and the plants may not have enough energy to flower the following year — or even return at all. This makes it very important to protect your lilies from damage.
Start scouting for lily beetles in late spring, shortly after your lilies emerge from the ground. If you see a flash of red, that’s what you’re after. You’ll need to sneak up and be prepared to grab very quickly. Drop the beetles into hot soapy water or use force to crush their shells. Inspect stems and leaves from all angles as the beetles hide in leaf crotches.
Destroying this pest’s eggs and larvae is equally important. Check your plants carefully at least 2-3 times a week, taking time to bend down and look under every leaf. Scrape off the larvae and remove the eggs — wearing tight-fitting rubber gloves makes this job a little less unpleasant.
There are two organic sprays that are relatively effective against the red lily leaf beetle. For both, spray coverage must be heavy and complete. Neem, an extract of the neem tree (Azadirachta indica), will kill young larvae. It should be applied every 5-7 days throughout early summer.
Spinosad, an insecticide made from soil bacteria, is also effective if applied weekly. As with all insecticides, it’s important to spray in the evening when bees are not foraging. Avoid spraying in windy weather when the spray may drift onto nearby flowers.
In Europe, parasitic wasps keep lily leaf beetle populations in check. Scientists at the University of Rhode Island have released several species of these predators in RI, MA, NH and ME. Over time, lily leaf beetle populations have declined in most of the test areas and the wasps are gradually spreading into neighboring towns. Hopefully this ecological approach will put a dent in the problem.
Plant Pest Resistant Types of Lilies
Some lilies seem to be more resistant to the lily leaf beetle than others. Research at the University of Maine found Lilium henryii ‘Madame Butterfly’, Lilium speciosum ‘Uchida’ and Lilium ‘Black Beauty’ showed better than average resistance.
Don’t Give Up the Battle – Lilies are Worth the Investment
If you live in an area where the lily leaf beetle is a problem, don’t despair. A combination of hand-picking and spraying the foliage weekly for at least the first half of the summer can keep this pest under control. The reward is months of beauty and fragrance that no other flowers can match.