The scarlet lily leaf beetle can denude a beautiful lily. Luckily, there are methods to deal with them. Wikipedia

North country know-how helps beat lily leaf beetle

The lily, native around the world in the temperate parts of the northern hemisphere, has been an important cultural icon for millennia. Depending where you stand on the globe, it can represent humility, purity, unbridled sexuality, the province of Québec, wealth or a thriving garden, to name but a few possibilities.

The flower is mentioned in the New Testament, such as in Matthew 6:26: “Behold the lilies of the field: They toil not, they spin not; and yet I say unto you, that Solomon in all his glory was not arrayed like one of these.” The message, as I understand it, is that one should not waste energy worrying how to clothe oneself, because even wild lilies are garbed well.

Unfortunately, Northern New York has a relatively new pest which specializes in denuding lilies. The lily leaf beetle (LLB) is a fiery-red native of Asia and Europe which has a voracious appetite for true lilies, those in the genus Lilium, as well as for their relatives the fritillaries (LLB does not eat daylilies). First found in New York state in 1999 by two Cornell master gardeners in Clinton County, the lily leaf beetle has slowly spread across the state over the past 20 years, much to the dismay of flower enthusiasts.

Adult LLB range from ¼ to ⅜ of an inch long and have prominent antennae. The adults, which overwinter in the soil, start feeding as soon as the lilies begin to appear. They mate, lay eggs and die early in the season, but their larvae soon emerge to wreak more havoc. At roughly 12 mm or a half-inch when full-size, LLB larvae can be yellow or orange, but you’d never know it because they smear their poop all over themselves to deter predators. It is a strategy that works well on gardeners, and somewhat on birds. Later in the season, the larvae pupate and emerge as beetles, which again go after the poor lilies. It has gotten so bad that some gardeners have given up on lilies.

But in St. Lawrence County, a few lily growers have successfully fought back and won. In 2015, Paul Siskind, a musicologist by training as well as a Cornell master naturalist, wanted to find the best organic spray to control this novel pest. To his surprise, Siskind found there had been little research done on LLB, and none at all on his topic of interest. He devised a study comparing the effectiveness of common organic products, and also recorded relative numbers of LLB found on four different strains of lilies to see which were preferred by LLB.

The short story is that a product called Spinosad, made of compounds produced by certain bacteria, provided good control of lily leaf beetles. Though it is less toxic than many other insecticides, it is important to follow label directions. Neem oil, derived from a tropical tree, is listed as effective against LLB larvae, but Mr. Siskind found that only neem products which were labeled “cold-pressed” had any effect. Diotomaceous earth, often suggested as a control, had a negligible impact on LLB.

Mr. Siskind also noted that LLB strongly prefer Asiatic-type lilies such as “Orange County,” with trumpet lilies like “African Queen” in second place. Oriental varieties were even less palatable, and lily leaf beetles showed the least interest in the Oriental x Trumpet crosses such as “Conca d’Or.”

Hand-picking, unpleasant though it is, can also provide good LLB control, and is the cheapest and safest option by far. Guy Drake of Heuvelton, a longtime producer of perennial flowers and shrubs, believes that you want to beat LLB, you simply have to “garden up,” in his words. Mr. Drake, who can be found at the Canton Farmers Market twice a week, told me that the scarlet-red beetle devastated his lily selection when they first showed up at his place several years ago. The following year he began to diligently scout for LLB eggs, larvae and adults every morning. Since then, he has been virtually beetle-free.

The secret, he said, is to hand-pick very early in the morning. The reason it’s essential to get out early is because adult beetles have a unique defense mechanism. As soon as you approach, they drop off the plant, land upside-down on the ground, and lie still. Though red on top, underneath they are tan, making them almost impossible to find. But in the cool of early morning, he says they don’t move, and can be easily swept into soapy water or crushed.

In the long-term, biological controls may keep LLB populations so low that they cease to be a threat to lilies. In 2017, the New York State Integrated Pest Management program at Cornell’s College of Agriculture and Life Sciences, in conjunction with Cornell Cooperative Extension, released three species of tiny parasitic wasps in Putnam and Albany counties, as well as on Long Island. Researchers from NYS IPM say that it will be a slow process, but they are optimistic that natural LLB control will happen in the coming decades.

In the meantime, we’ll need to help lilies keep their splendid garments from being consumed by lily leaf beetles. Garden up, everyone.

Paul Hetzler is a natural resource and horticultural educator with Cornell Cooperative Extension of St. Lawrence County. Contact him at 315-379-9192 ext. 232.

Johnson Newspapers 7.1

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(2) comments


It might have been somewhat important to let us know how the beetles damage the plant. Do they eat the leaves like Japanese beetles, or doe the larvae eat the bulbs? One hint came from the term "denude", suggesting that the leaves are the target. If they overwinter in the soil, what should fall management look like? I guess I will have to find out on my own.

Paul Siskind

Both the beetle and the larvae eat the leaves; they don't eat the bulbs. The beetles do a fair bit of damage, but the larvae really decimate the plant. The beetles (but not the larvae) overwinter in leaf litter on the ground. They mate and lay eggs as soon as the lilies start sprouting in spring. The eggs hatch in about 2 weeks. The larvae eat for about 2 weeks, then crawl into the ground to pupate. They emerge as beetles in about 3 weeks. By the time these new beetles emerge in July, the old generation has stopped laying eggs for the year. So, there are three "waves" of an infestation every year: 1) old adults, May-June; 2) new larvae, June-July; 3) new adults, July-Oct. We don't know if the old beetles live on for another year. In fact, we're finding reports that beetles in North America mate and possibly lay eggs again in August, which they don't do in their native Europe. So, to answer your question about management in the fall: The critical thing to do is to manage them in the spring, as soon as they emerge from hibernation and start mating. Damage that the beetles and larvae do to the leaves in spring makes the leaves dry out in summer, and the plant can't store energy in the bulbs. Because of the compressed life-cycle, if you are thorough about killing adults before they lay eggs, and are also thorough about killing the larvae before they pupate, then you won't have a lot of beetles from July-Oct (although the new beetles seem to fly around to new plots for food, so you might get newcomers); keep killing them to lessen the number of adults that will winter over. My recommendation is to hand-pick as many beetles/larvae as you can, to lessen the amount of insecticide you use. The beetles fall off of leaves when they see a shadow, so cup your hand under to cath them. The larvae cover themselves with their own excrement, so it's disgusting to try to pick them off; flicking is less disgisting, but it's hard to be thorough because the larvae stay on the underside of the leaves. After hand-picking, use spinosad about twice a week until the larvae are gone (around mid-July); then you can cut back to once a week for the rest of the summer. Spray only the lilies (leaves, not flowers), and you can aim directly at the beetles/larvae. Avoid spraying when it's windy, or at during the hot afternoon. You don't need to drench the plant; a fine mist is enough. You'll never totally eradicate the beetle, but the goal is to control them well early in the season, so that the plants keep some healthy leaves throughout the summer. If you do a thorough job, you'll notice a difference the second summer; and if you keep at it, you can keep the beetles at a manageable level and have relatively healthy lilies.

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