Lily Leaf Beetle

Lily Leaf BeetleLilies have long been favored by gardeners in the Northeast for their unsurpassed beauty and relative ease of maintenance. The recent arrival of the lily leaf beetle in Boston has complicated lily culture and gardeners throughout the area should be on the lookout for this insect. The lily leaf beetle, native to Europe, was discovered near Montreal, Canada in 1945. Its damage was limited to the Montreal area for decades, but recently it has spread to the south and west. They have spread as much as 150 miles from Boston, in many cases with the assistance of gardeners.

At present the infested area in the USA reaches into all of the New England states, including southern Connecticut and northern Vermont. Not all areas are yet infested and gardeners who are transplanting bulbs and other garden plants should be careful not to move these beetles to an uninfested area.

The adult beetle emerges from the soil in early spring. Females lay irregular rows of yellow-orange cylindrical eggs on the undersides of leaves of young lily plants. The eggs hatch in a week to 10 days under normal conditions. Females lay up to 450 eggs, sometimes over two growing seasons.Larvae cause more damage than adults, feeding for 16-24 days, primarily on the undersides of leaves before entering soil to pupate.New adults emerge from their florescent orange pupae in 16-22 days and feed until fall.

Adult beetles overwinter in the soil or plant debris in the garden or woods, sometimes a distance away from the host plants, preferring environments that are shaded, protected, cool, and moist. They do not mate or lay eggs until they emerge the following spring.Although the beetles may feed lightly on many plants, including Fritillaria sp., Polygonatum sp.(Solomon’s seal), Solanum dulcamara (bittersweet nightshade), S. tuberosum (potato), Smilax sp., Nicotiana sp., Alcea (Hollyhocks) and Hostas, they lay eggs and develop only on Liliuim and Fritillaria species.They do not attack daylilies.

Damage :If your customers only have a few plants in their garden, hand-picking adults and eggs can be effective. For more than a few susceptible plants, pesticide treatments may be needed. Products containing Neem (Bon-NeemTM, AzatinTM), a botanical insecticide, have been shown to kill very young larvae but must be applied every five to seven days after egg hatch. Products containing the systemic imidacloprid are reportedly providing effective control applied either as a foliage spray or soil drench depending on label instructions.

Imidacloprid is the active ingredient in MarathonTM, used by commercial flower growers, MeritTM, used by landscapers and home gardeners and one of the active ingredients in Bayer Advanced Rose and Flower Insect Killer for home gardeners. There are also other home gardener formulations containing imidacloprid. Products containing spinosad a microbial insecticide, may also be effective. Spinosad is sold as ConserveTM and EntrustTM for commercial growers and Monterey Garden Insect SprayTM, BULL’S-EYETM and others. Before recommending a product or applying any pesticide, read the label and apply only as directed on the label.

Hand-picking adults, eggs, and larvae is an effective means of reducing damage. It’s important to begin scouting for emergence of adults in April, and destroy any that you see. As spring progresses, check the undersides of leaves for orange egg masses and destroy them as well. Remove young larvae from leaves as they develop. Wear a tight-fitting rubber glove if you want to avoid directly touching the eggs or larvae. Make this practice a regular routine throughout the summer months, as it is a very effective control tactic.

Neem, an extract of the neem tree (Azadirachta indica), is the active ingredient in the organic insecticides Turplex, Azatin EC, Margosan-O, Align and Bio-Neem. Neem is most effective on first-stage, very young LLB larvae, and should be applied every five to seven days after eggs begin to hatch. The systemic synthetic insecticide imidacloprid (Merit) also provides effective control when applied to the soil in early spring. Malathion is an effective chemical spray for adults and larvae. Follow the directions on all pesticide labels closely.

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