Elm Leaf Beetles Fact Sheet No

Elm Leaf Beetles Fact Sheet No. 5.521 Insect Series|Trees and Shrubs by W.S. Cranshaw* Elm leaf beetles (Xanthogaleruca Quick Facts luteola) are common insects that chew leaves of elm trees (Figure 1). The dark • Adult elm leaf beetles grub-like larvae chew on the underside chew holes in elm leaves. of leaves but avoid the larger leaf veins, The larvae feed on the producing a type of injury pattern known leaf surface, producing as skeletonizing (Figure 2). Leaves skeletonizing injuries that damaged by elm leaf beetle larvae look make leaves look lacy. lacy, turn brown and may prematurely drop from the trees (Figure 3). Adult • Adult elm leaf beetles often beetles chew irregularly round holes spend winter in and around in the center of leaves. Siberian and buildings and may be English elms are particularly favored by common nuisance invaders this insect. found within homes during Elm leaf beetles also can be Figure 1. Elm leaf beetle adults and damage. this period. important as a nuisance pest in homes, because they often enter buildings in • Some insecticides that move autumn when seeking winter shelter. systemically within plants Beetles that do work their way behind can be applied to the soil to walls and other areas of buildings may control elm leaf beetles. then be found indoors until spring, becoming most active during warm periods. Fortunately elm leaf beetles are strictly a nuisance invader type of insect that does not feed on nor damage anything within a home, although their very presence in a home is a common cause of concern. Historically elm leaf beetles have Figure 2. Skeletonizing injury to elm leaves produced by elm leaf beetle larvae. been a major insect in Colorado communities where ever elm trees are weevil produces some leaf injuries, such common. However, since the mid- as shotholes in leaves, which are similar 1990s, incidence of problems has to those produced by adult elm leaf declined in most areas of Colorado. In beetles. This new insect of elms is occurs recent years problems have most often throughout the state and is discussed at the occurred in towns along the Arkansas end of this sheet. River Valley, less commonly occurring as spot outbreaks elsewhere in eastern Colorado. Life History and Habits Beginning around 2006 an additional Elm leaf beetles overwinter in the beetle arrived in Colorado that feeds adult (beetle) stage. In late summer and on elm, the European elm flea weevil early autumn they seek out protected © Colorado State University (Orchestes alni). European elm flea sites such as woodpiles, loose mulch, Extension. 11/96. Revised 1/18. and piled eaves to shelter through extension.colostate.edu winter. Often cracks and other openings *W.S. Cranshaw, Colorado State University Extension that allow them to get behind building entomologist and professor, bioagricultural sciences and walls serve as winter shelters. During pest management. 1/2018 Table 1. Insecticides that can be used to control elm leaf beetles. Products are listed by Active Ingredient (in bold). Some trade names/ formulations of these insecticides are listed in parentheses. Soil applied systemic insecticides Imidacloprid (Bayer Advanced Tree & Shrub Protect & Feed Concentrate II, Bonide Annual Tree & Shrub Control, ferti-lome Tree & Shrub Systemic Insect Drench; Ortho Bug B Gon Year-Long Tree & Shrub Insect Control, Merit, Mallet, Zenith, Criterion, others) Chlothianidin (Bayer Advanced Tree & Shrub Protect & Feed Concentrate II, Arena) Figure 3. Trees showing leaf injury by elm leaf beetle. Insecticides applied as sprays to leaves Azadirachtin (Azatin, AzaGuard, Azasol, BioNeem, others) Bifenthrin (Talstar, Onyx, Ortho Bug B Gon Insect Killer for Lawns & Gardens) Carbaryl (Sevin, Carbaryl) Cyfluthrin (Tempo, Bayer Advanced Vegetable & Garden Insect Spray) Cyhalothrin (Scimitar, Spectracide Triazicide Insect Killer for Lawns & Landscapes, Cutter Backyard Bug Control Spray Concentrate Permethrin (Astro, Permethrin, Hi-Yield Turf, Termite and Ornamental 38 Plus, Bonide Eight Insect Control Yard & Garden, others) Spinosad (Conserve, Bonide Captain Jack’s Dead Bug Brew, Natural Guard Spinosad Landscape & Garden Insecticide, ferti-lome Borer, Bagworm, Leafminer & Tent Caterpillar Spray) Tiny, black larvae hatch from these leaf beetle. There are small parasitic Figure 4. Elm leaf beetle adult, with the green coloration of the overwintering form. eggs and originally they will chew wasps that attack larvae and pupae, Photograph courtesy of Joseph Berger, small pits near where the eggs had although incidence of these appears to Bugwood.org been laid (Figure 7). As they get be very low in Colorado. Some pupae older and larger, elm leaf beetle larvae may be killed by Beauveria bassiana, a scatter through the tree. They feed on fungus that produces disease in many the underside of the leaf, avoiding the insects, but infections with this disease larger leaf veins, “skeletonizing” the require conditions of high humidity and leaves (Figure 8). outbreaks are uncommon in arid sites. Within 3 to 4 weeks after eggs are Weather probably is the most laid, the larvae are full grown and they important factor that affects elm leaf then wander to find sheltered spots beetle populations. Long winters or where they can transform to their next a late spring freeze may kill large stage, the pupa. Most crawl down numbers of overwintering beetles. the trunk and pupate at the base of Small larvae are susceptible to being Figure 5. Elm leaf beetle, with the yellow coloration of the form found during the the tree, sometimes in large groups blown or rubbed off trees during growing season. (Figure 9). Others may settle into some wind storms. This may be particularly of the larger fissures of the bark. common when larvae are forced to Within about two weeks, new adults feed on older, tough leaves. This emerge from the pupae. They then fly increases their wandering and many this period the beetles are in a semi- back to the leaves, mate, and produce die in the process. dormant state (diapause) and are a a second generation. There follows a second cycle of larvae chewing leaves khaki-green color (Figure 4). While Chemical Control in this dormant state they do not feed from mid-July into September. Adult nor reproduce but may become active beetles that are produced at the end Chemical controls can effectively during warm days in late winter and of this second generation will feed for control elm leaf beetles. These are spring. a brief while on leaves but do not lay best used in areas where outbreaks In spring the beetles that survived eggs. They then move to overwintering regularly occur or when large numbers winter become increasingly active shelter sites where they remain until of beetles are observed laying eggs, and move to elm trees when leaves the next spring. an indication of a potential outbreak. emerge. As the beetles feed their Insecticides can be employed in three ways to manage elm leaf beetle: 1) color shifts to more yellow-green and Natural Controls within a few weeks female beetles use of soil drenches/soil injections of begin laying eggs (Figure 5). The Few natural enemies feed on elm systemic insecticides that move to kill eggs are yellow, typically laid on the leaf beetles. Insect predators, such as insects on foliage; 2) use of sprays underside of leaves in masses of one predaceous stink bugs and plant bugs, covering leaves to directly contact or two dozen (Figure 6). may feed on various stages of the elm and kill larvae and adults; and 3) trunk banding with insecticides to kill larvae Sprayed Treatments. as they move to the base of the tree to pupate. Several insecticides (Table 1) can be used to control elm leaf beetles Soil Applied Systemic Insecticides. feeding on leaves. These treatments are best applied after most eggs are A few insecticides are systemic in laid by the overwintering females plants, capable of moving through but before the larvae start to cause the plant providing so that they may significant injury to the leaves. For control insects some distance from the first generation of elm leaf beetle where the insecticide is applied. in southeast Colorado this typically Most useful for control of elm leaf occurs in late May or early June. beetle are insecticides that can be Figure 6. Egg mass of an elm leaf beetle. Most of the insecticides applied applied to the soil and that then can as sprays will have several days of move to the leaves where elm leaf persistence in ability to kill elm leaf beetles feed. beetles. This can be a useful feature if Imidacloprid is the most many eggs remain unhatched when commonly available insecticide sprays are made. Other insecticides, that moves systemically in plants such as the neem-derived products and can be used in elm leaf beetle (azadirachtin) and biological control. Less commonly available is insecticides (spinosad) have short chlothianidin, a chemically related persistence and should be timed to material also in the neonicotinoid periods after egg hatch. class of insecticides (Table 1). These are used as a soil application Trunk Banding applied to areas where roots absorb the insecticide then move Figure 7. Elm leaf beetle larvae after egg hatch Some control of late season elm and associated leaf injury. the insecticide into and through the leaf beetle feeding injury is possible plant. These insecticides can be by spraying a band of insecticide applied as either soil drench around on trunks to kill larvae that crawl to the base of the tree or as a series the base of the tree when they have soil injections spread to areas under finish the first cycle of feeding in the crown. Rates of insecticide are early summer. The bands should be indicated in label instructions and are at least one foot wide and placed usually indicated as being related on the trunk just below where the to either the diameter (commercial lowest major branches join the trunk.

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