Integrated Pest Management for Landscape Professionals and Home Gardeners
Elm leaf beetle, Xanthogaleruca (=Pyrrhalta) luteola, is one of the most important insects damaging urban for- ests in the United States and is the ma- jor pest of elm trees in California.
IDENTIFICATION Adults are olive-green beetles with black, longitudinal stripes along the margin and center of the back (Fig. 1). Females lay their yellowish to gray eggs in double rows of about 5 to 25 on the underside of leaves. Larvae are black when newly hatched. After feeding, they become a dull yellow or green with rows of tiny, dark tubercles (pro- jections). Larvae develop through three stages called “instars.” Third-instar larvae have dense rows of dark tu- bercles that resemble two black stripes down their sides, making them easy to distinguish from first- and Figure 1. Elm leaf beetle adult and eggs (5×), and third-instar larvae and second-instar larvae. Mature third in- damage (life size). stars are up to 1⁄3 inch long. Pupae are orange to bright yellow. DAMAGE Recognize that elm leaf beetle populations Elm leaf beetle is a serious defoliator of fluctuate dramatically from year-to-year and LIFE CYCLE elms. Larvae skeletonize the leaf sur- most trees do not require treatment every Adults commonly overwinter in bark face, while adults chew entirely year. When beetles are present, other- crevices, litter, woodpiles, or in build- through the leaf, often in a shothole wise healthy elms can tolerate substan- ings. They fly to foliage in spring and pattern. Defoliation eliminates summer tial defoliation. Where elm leaf beetle is feed and lay yellowish eggs, which shade, reduces the aesthetic value of a problem, use a combination of meth- become grayish before hatching. After trees, and causes annoying leaf drop. ods because no single method kills 100% feeding in the canopy for several weeks, Repeated, extensive defoliation weak- of the pests. Relying solely on the same mature larvae crawl down the tree ens elms, causing trees to decline. technique year-after-year selects for pest trunk, become curled, inactive populations less susceptible to that prepupae, and then develop into yel- MANAGEMENT treatment. Because adult beetles fly lowish pupae (Fig. 2). After about 10 Manage elm leaf beetle with an inte- from tree to tree, management efforts days, adult beetles emerge from pupae grated program that incorporates good directed at single trees may give less around the tree base and fly to the cultural practices, conservation of natu- satisfactory results in comparison with canopy to feed and (during spring and ral enemies, regular monitoring, the use control efforts aimed at all elms in an summer) lay eggs. Elm leaf beetle has at of less-toxic insecticides (e.g., Bacillus area. Because elms are large trees and least one generation a year in northern thuringiensis subspecies tenebrionis), because this pest is difficult to control, California and two to three generations bark banding with insecticides, or sys- pesticide treatment is best done by a in central and southern California. temic insecticides. professional applicator.
PEST NOTES Publication 7403 University of California Agriculture and Natural Resources Revised November 2001 November 2001 Elm Leaf Beetle
Cultural Control Good cultural care of trees is an essen- tial component of integrated pest man- egg cluster agement. European and American elm (actual species are adapted to summer rainfall; size) they require proper irrigation to grow first instars well in California. Protect elms from injury to trunks and roots. Check elms for dead or dying branches and prop- adult erly prune these out during late fall and winter. Avoid pruning elms dur- second instar ing spring and summer; the European elm bark beetle (Scolytus multistriatus), which vectors Dutch elm disease (Ophiostoma [=Ceratocystis] ulmi), is pupa attracted during spring and summer to prepupa feed around fresh pruning wounds. English elm (Ulmus procera) and Scotch third instar elm (U. glabra) are especially suscep- tible to both elm leaf beetle and Dutch (actual size) elm disease (Table 1). Do not plant these species and consider replacing them in areas where they are growing. Figure 2. Elm leaf beetle stages and life cycle. Treatment Thresholds Using treatment thresholds to deter- Table 1. Susceptibility of Elms and Elm Substitutes to Elm Leaf Beetle (ELB) mine if control is needed helps mini- and Dutch Elm Disease (DED). mize unnecessary insecticide applications, avoid or reduce annoy- TREE SUSCEPTIBILITY ance from beetle damage, and protect Common name Scientific name ELB DED elms, especially when trees are already English elm Ulmus procera HS HS stressed or unhealthy from other Scotch elm U. glabra HS HS causes. Healthy elm trees can tolerate American elm U. americana SHS substantial damage to leaves; even ‘Homestead’ complex hybrid including S R total defoliation may have little long- U. carpinifolia, U. hollandica, term effect on healthy elms, especially and U. pumila if leaf damage comes late in the season. ‘Liberty’ group U. americana selections S1 MR Suggested treatment thresholds are American elms 40% defoliation (portion of leaf area ‘New Horizon’ and U. americana selections S1 R chewed or leaves dropped prema- ‘Valley Forge’ turely) or 20% defoliation if damage is American elms less tolerable. ‘Pioneer’ U. glabra X U. carpinifolia SR Siberian elm U. pumila SMR Monitoring ‘Frontier’ U. carpinifolia X U. parvifolia MR2 R When using insecticide bark bands, Chinese elm U. parvifolia RMR foliar sprays, or trunk injection of a ‘Prospector’ U. wilsoniana selection R R systemic insecticide, monitor elm trees zelkova Zelkova serrata RMR to determine the need for treatments hackberry Celtis spp. NS NS and when to apply them. Evaluate hornbeam Carpinus spp. NS NS beetle populations during spring by inspecting foliage weekly for beetles HS = highly susceptible R = resistant starting in April. Watch for the appear- S = susceptible NS = not susceptible MR = moderately resistant ance of yellowish eggs, which darken 1. Generally susceptible to elm leaf beetle, but certain selections exhibit some resistance. before hatching. If trunk injections of 2. Reported susceptibility to elm leaf beetle ranges from susceptible to resistant, possibly due systemic insecticides (e.g., abamectin to location, genetic variability among plants, or misidentification of elms. or imidacloprid) are the planned con- trol method for a large number of trees,
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Table 2. Criteria to Help Decide if Preventive Systemic Insecticide Is Warranted for Elm Leaf Beetle Control.
Criteria Avoid treatment Treatment may be warranted beetle populations and damage the low population or damage high population or damage previous late summer/early fall treated the previous season yes no overwintering weather wetter or warmer than average, or both drier or colder than average, or both
± Table 3. Time of Peak Abundance (Mean Standard Deviation) of Elm Leaf leaves appear in spring. If elm leaf Eggs and Larvae in Northern California Based on Degree-Day (DD) beetle damage was low the previous Monitoring. fall and the winter is warm and wet, First generation DD (F) avoid preventive insecticide applica- eggs 509 ±95 tion the subsequent spring. first-instar larvae 635 ±112 Degree-Day Monitoring. Insect activ- second-instar larvae 794 ±162 ity and growth rate depend on tem- third-instar larvae 857 ±167 perature. Generally, the higher the Second generation temperature, the more rapid the devel- ± eggs 1,715 167 opment. Measuring heat over time ± first-instar larvae 1,962 131 provides a physiological time scale second-instar larvae 2,055 ±158 called degree-days that is more useful third-instar larvae 2,129 ±162 than calendar days for timing insect monitoring and control. Degree-days are above 51.8°F (11°C) accumulated from March 1. See the UC Statewide IPM Project’s Web site at http://www.ipm.ucdavis.edu for more information. Adapted from Dahlsten et al. 1993. One degree-day is defined as one de- gree above the threshold temperature maintained for a full day. The lower threshold for elm leaf beetle is 51.8°F consider using egg presence-absence and before knowing if beetles will be (11°C). When temperatures are cooler, sampling and injecting the trees as abundant enough to warrant control this pest does not feed, grow, or repro- soon as monitoring indicates thresh- during the current or next generation duce. To predict the peak abundance of olds will be exceeded. If a foliar insecti- of insects. Use several criteria to help each life stage, degree-days above cide application is planned, spray decide if a preventive, soil-applied 51.8°F are accumulated for elm leaf when early instar (small) larvae are insecticide is warranted (Table 2). For beetle each season beginning March 1 abundant. Band bark with an insecti- example, inspect elms during late sum- (Table 3). If populations are high and cide before mature larvae crawl down mer to early fall; if beetles and damage damage is anticipated, treatment op- trunks to pupate, which in California are low, especially on untreated elms, tions include injecting elms as soon as may occur from early May to late June, it is less likely that insecticide applica- need is predicted (based on monitoring depending on the location and tion is needed next season. egg abundance) or applying a trunk weather. Inspect foliage weekly during spray or foliar spray at about 700 de- May and June and band as soon as Although it has not been scientifically gree-days (Table 4). mature larvae are observed on leaves. demonstrated, relatively warm and The calendar date of peak abundance wet winters are believed to reduce the Temperatures for many locations and of beetles and their damage and the likelihood that beetles will be a prob- relatively easy to use degree-day calcu- optimal time for banding varies greatly lem the following spring. Wet winters lation tools are available from the UC from year-to-year, depending on previ- can increase overwintering mortality of Statewide IPM Project’s Web site at ous temperatures (spring weather). beetles from insect pathogenic fungi. http://www.ipm.ucdavis.edu. Alter- Monitoring temperature is highly rec- Warm winters may cause many “hiber- natively, dedicated devices can record ommended to more accurately time nating” beetles to starve to death be- temperatures and calculate degree- foliage inspection and control actions. cause warmer weather increases the days. If temperature records are avail- rate at which these insects consume able, a programmable calculator, If an application of a soil systemic in- their stored energy (e.g., body fat), desktop computer, or printed charts for secticide is planned, the optimal treat- increasing the likelihood that beetles certain pests can also be used to calcu- ment time is before beetles are present become weakened or starve before elm late degree-days.
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Table 4. Timing of Elm Leaf Beetle Monitoring, Bark Banding, Foliar Sprays, or Systemic Insecticide Injection Based on Degree-days (DD).
DD (F) 1st DD (F) 2nd Action Justification generation generation sample eggs once a week when using egg density to predict 329–419 1,535–1,625 treatment need two or more Btt applications first & second instars present 550–800 not recommended at 7- to 10-day intervals single foliar spray peak density of first & second instars combined 700 not recommended trunk spray or bark banding before earliest third instars crawl down trunk 700 2,000 systemic insecticide injection as soon as possible if egg sampling during 329 to 419 DD indicates thresholds are exceeded — not recommended
Degree–days are above 51.8°F accumulated from March 1. See the UC Statewide IPM Project’s Web site at http://www.ipm.ucdavis.edu for more information. Adapted from Dahlsten et al. 1993.
Presence-Absence Sampling for Pro- of samples infested by the total num- holes in beetle pupae may indicate that fessionals. The percent of 1-foot ber of samples inspected and multiply this parasite has emerged. An egg branch terminals infested with elm leaf by 100. parasite, Oomyzus (=Tetrastichus) beetle eggs can be used to determine gallerucae, leaves round holes when it treatment need when a large group of Time control actions as discussed emerges from beetle eggs, which re- trees is being monitored. Using a above and summarized in Table 4. For main golden. When beetle larvae have threshold of 40% defoliation, treatment more details on presence-absence egg emerged, the egg shell is whitish with is warranted when over 45% of branch sampling, consult the publications by more ragged holes. For illustrations terminals have beetle eggs during the Dahlsten and others or Pests of Land- and photographs of elm leaf beetle week when egg density is at its maxi- scape Trees and Shrubs listed in parasites, consult Natural Enemies mum during the first generation. If the “References.” Handbook listed in “References.” preferred threshold is 20% defoliation, treatment is warranted when over 30% Biological Control Conserve these parasites and general of branch terminals are egg-infested Several introduced and native natural predators by avoiding foliar applica- during the first generation. enemies kill elm leaf beetles, but gener- tions of broad-spectrum insecticides; ally do not provide adequate control use less toxic materials such as Bacillus Use a pole pruner to clip two or more by themselves. The most important thuringiensis ssp. tenebrionis (Btt), Btt 1-foot terminals from each of eight parasite in California is a small, black and narrow-range oil combined, or locations in the lower canopy of each tachinid fly (Erynniopsis antennata) that apply insecticide as bark bands in an sample tree. Locations are north, east, emerges from mature beetle larvae. Its integrated program to obtain maxi- south, and west, in both the inner black to reddish, cylinder- or teardrop- mum benefits from biological control. canopy (from trunk halfway to the shaped pupae occur during spring and drip line) and the outer canopy. Ran- summer at the base of trees among the Chemical Control domly select the trees to be sampled yellowish beetle pupae. Erynniopsis Methods for chemical control of elm and sample those trees each week. antennata overwinters in adult beetles, leaf beetle include bark banding, soil Inspect a minimum of 120 total emerging as adults in spring, although applications, tree injection, or foliar samples, two to five terminals from this is not readily observed. Unfortu- spraying in spring after monitoring each location of three or more trees. nately, the effectiveness of E. antennata beetle abundance to determine treat- is limited by Baryscapus (=Tetrastichus) ment need. Examine the leaves on each sample erynniae, a secondary parasite and record whether eggs are present or (hyperparasitoid) that kills the benefi- Bark Banding. Bark banding is an in- absent. Once you observe the first eggs cial parasite. expensive and environmentally sound on a sample, there is no need to exam- technique that involves spraying a ine it further; record it as infested and Two tiny wasps also parasitize elm leaf small area of the tree trunk with an move on to inspect the next terminal. beetle. Oomyzus (=Tetrastichus) insecticide. Use a hand-pump sprayer To determine the percent of samples brevistigma parasitizes mature larvae or hydraulic sprayer at low pressure to (terminals) infested, divide the number and pupae; one or more small, round spray a band of bark several feet wide
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around the first main branch crotch. Also, overwintered adults fly to the cleaning and disinfecting tools to re- Carbaryl (Sevin) is most commonly tree canopy and lay eggs, so trunk duce the chance of spreading patho- used and should be applied at the rate banding does not reduce the first gen- gens when injecting or implanting labeled for elm bark beetles (about 2% eration of beetles and their damage. A multiple elms. Before chemical disin- active ingredient). If trunk spraying is study of elm trees in northern Califor- fection, remove all plant material and not listed on the label of the commer- nia found good control during the first scrub any plant sap from tools or cial products available for home land- season of bark banding on Siberian equipment that penetrate trees. Bleach scape use, it will be necessary to have elms (Ulmus pumila), but not on En- (and, to a lesser extent, certain other the trunk application done by a li- glish elm and Scotch elm. If beetles are materials) can be effective disinfectants censed pesticide applicator. Do not use abundant during the first generation, if applied to debris-free tools. At least 1 the rate labeled for foliar applications little or no control should be expected to 2 minutes of disinfectant contact because this rate will not be effective as the first year when banding more sus- time between contaminated uses is a trunk banding treatment. Pyrethroids ceptible species such as English and generally required. Consider rotating (e.g., fluvalinate) also provide control. Scotch elms; banding all nearby elms work among several tools, using a About one-half gallon of dilute mate- for several consecutive years can pro- freshly disinfected tool while the most rial is applied on each large tree. Lar- vide control after the first year of recently used tools are being soaked in vae are killed by the insecticide when treatment. disinfectant. crawling down to pupate around the tree base after feeding in the canopy. Systemic Insecticides. Elm leaf beetle Imidacloprid is available to both home By reducing the number of elm leaf feeding can be controlled with certain gardeners and professionals for appli- beetles that pupate and emerge as systemic insecticides, including cation on or into soil beneath trees. The adults, bark banding reduces damage abamectin (Avid, Vivid II), acephate most effective time to apply it is early by later beetle generations, especially (Orthene), and imidacloprid (Bayer spring, just before new leaves emerge. when done to all nearby elms. Advanced Tree & Shrub Insect Control, Make an application before a rainfall, Imicide, Merit). Some formulations of or follow the application with irriga- You can determine the best time to these materials can be sprayed onto the tion. Although efficacy is delayed until spray the trunk by inspecting the foli- tree foliage, but soil applications and sometime after application, it usually is age and spraying when mature larvae tree injections (if labeled for this not necessary to treat 2 years in a row are first observed, or for more accurate method of application) minimize envi- using this method. A major disadvan- timing, by accumulating degree-days ronmental contamination and may be tage of this timing is that treatment is and spraying the trunk band when more effective than foliar sprays. Tree- made before beetles appear in spring, about 700 degree-days (above 52°F) injected insecticides generally are before knowing whether insects and have accumulated from March 1. A available only to professional applica- damage will be abundant enough to single application of carbaryl to the tors. warrant control action. Consult the bark each spring can kill most larvae suggested criteria for help in deciding that crawl over it all season long. A When using systemic insecticides, con- whether preventive treatment is war- second application may be necessary if sider using a soil application instead of ranted (Table 2). Soil applications are substantial rain occurs after applica- spraying foliage or injecting or im- possible even if trees are surrounded tion, if trunks are frequently wetted by planting trees whenever possible. In- by pavement. Depending on the prod- sprinklers, or if a less persistent mate- jecting or implanting trunks or roots uct label directions, the insecticide can rial is used. To determine if the bark injures trees, and it is difficult to re- be applied to soil immediately adjacent band is still effective, regularly inspect peatedly place insecticide at the proper to the trunk or nearby bare soil, lawn, around the base of trees throughout depth. Especially avoid methods that or planting beds where most absorbing the season. If many beetles have cause large wounds, such as implants tree roots usually occur. changed from greenish prepupae (the placed in holes drilled in trunks. Do stage killed by banding) to bright yel- not implant or inject roots or trunks Foliar Sprays. Several foliar insecticide lowish pupae (unaffected beetles), more than once a year. sprays are available for elm leaf beetle. another application may be warranted. Foliar spraying may be appropriate to Avoid methods that use the same de- supplement banding during the first Bark banding alone will not provide vice (such as drills or needles) to con- year or two of treatment or when early- satisfactory control in all situations, tact internal parts of more than one season beetle populations are high. The especially if only one or a few trees are tree. Contaminated tools spread elm low-toxicity insecticides Bacillus treated. Adult beetles can fly between tree pathogens, including bacteria thuringiensis ssp. tenebrionis (Btt) or treated and untreated trees, so bark (such as slime flux or wetwood) and azadirachtin (Neemazad) are good banding is most effective when done fungi (Dutch elm disease). Before mov- choices in an integrated pest manage- on all the elm trees in a neighborhood. ing to work on each new tree, consider ment program. Btt can be combined
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with narrow-range oil to kill beetle cialized equipment is required to spray REFERENCES eggs and other elm pests such as the tops of large elm trees, it is best to Dahlsten, D. L., D. L. Rowney, and A. scales. More persistent, broad- hire a professional applicator. B. Lawson. 1998. IPM helps control elm spectrum materials, including carbaryl leaf beetle. Calif. Agric. 52(2):18–24. and pyrethroids, are also available for Bacillus thuringiensis ssp. tenebrionis foliar application, but are generally not (Btt) kills young beetle larvae and is Dahlsten, D. L., S. M. Tait, D. L. recommended because of their nega- the only truly selective insecticide Rowney, and B. J. Gingg. 1993. A moni- tive impact on natural enemies and available. Btt is not toxic to people and toring system and developing ecologi- their potential for environmental im- most nontarget organisms, including cally sound treatments for elm leaf pacts in urban settings. Carefully time natural enemies of the elm leaf beetle. beetle. J. Arboriculture 19:181-186. all foliar applications to target first- Btt (Novodor) is EPA registered for use and second-instar larvae. Because spe- in most states, but may not be available Dreistadt, S. H., D. L. Dahlsten, D. L. (registered) for use in California. Bt Rowney, S. M. Tait, G. Y. Yokota, and subspecies labeled for moth and but- W. A. Copper. 1991. Treatment of de- terfly caterpillars or mosquito larvae structive elm leaf beetle should be For more information contact the University are not effective against elm leaf beetle. timed by temperature monitoring. of California Cooperative Extension or agri- Calif. Agric. 45(2):23-25. cultural commissioner’s office in your coun- ty. See your phone book for addresses and To obtain control, foliage throughout phone numbers. the tree must be thoroughly sprayed Dreistadt, S. H., J. K. Clark, and M. L. with Btt during warm, dry weather Flint. 1994. Pests of Landscape Trees and AUTHORS: S. H. Dreistadt, D. L. Dahlsten, when young larvae are actively feed- Shrubs: An Integrated Pest Management and A. B. Lawson ing. Because only a portion of the Guide. Oakland: Univ. Calif. Agric. EDITOR: B. Ohlendorf TECHNICAL EDITOR: M. L. Flint beetle population is in the susceptible Nat. Res. Publ. 3359. DESIGN AND PRODUCTION: M. Brush stages at any one time and Btt breaks ILLUSTRATIONS: Fig. 1: Linda Heath down within several days, at least two Flint, M. L., and S. H. Dreistadt. 1998. Clark, CDFA applications at an interval of about 7 to Natural Enemies Handbook: The Illus- Fig. 2 adult, first instar, second instar: L. O. 10 days may be necessary beginning trated Guide To Biological Pest Control. Howard. 1895. The Shade-tree Insect Prob- when young larvae are first observed Oakland: Univ. Calif. Agric. Nat. Res. lem in the Eastern United States.Yearbook of the USDA. Washington, D. C. feeding (Tables 3, 4). Publ. 3386. Fig. 2 egg cluster, prepupa: F. Silvestri. 1910. Contribuzioni alla conoscenza degli insetti dannosi e dei loro simbionti. Bolletti- no del Laboratario di Zoologia Generale e Agraria Portici 4:246–289. Fig. 2 third instar: John Muir Institute. 1979. The Elm Leaf Beetle. Berkeley, CA. Fig. 2 pupa: G. W. Herrick. 1913. Control of Two Elm-Tree Pests. Cornell Univ. Agric. Exp. Sta. Bull. 333.
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