Pests in Gardens and Landscapes
Elm Leaf Beetle
The elm leaf beetle, Xanthogaleruca (=Pyrrhalta) luteola, is a leaf-chewing pest of elm bushes, particularly European elm species. American and most Asian elm species are much less severely fed upon. Most Chinese language elm cultivars, zelkova, and many more recent elm cultivars are occasionally fed upon.
Adults are 1/Four inch lengthy, olive-green beetles with black, longitudinal stripes alongside the margin and middle of the again. Females lay yellowish eggs in double rows of about 5 to 25 on the underside of leaves. Eggs develop into grayish earlier than hatching. Larvae resemble caterpillars and are black when newly hatched and shortly after molting (shedding the outdated pores and skin). After feeding, larvae develop into yellowish to inexperienced with rows of tiny darkish tubercles (projections). Third-instar larvae develop as much as 1/Three inch lengthy and have dense rows of darkish tubercles down their sides that resemble two black stripes. Pupae are orange to vibrant yellow.
The elm leaf beetle develops via 4 life levels: egg, larva, pupa, and grownup. Adults generally overwinter in bark crevices and woodpiles or in buildings. In spring they fly to elm foliage and chew leaves, and females lay eggs. Eggs hatch into larvae that develop via three instars (development levels) over a interval of a number of weeks whereas chewing on foliage after which crawl down the tree trunk. Mature larvae develop into curled and inactive (a stage known as prepupae), then pupate, typically in massive numbers, across the tree base. After about 10 days as pupae, adults emerge and fly to the cover to feed and, throughout spring and summer time, lay eggs. The elm leaf beetle has not less than one technology a yr in northern California and two to 3 generations in central and southern California.
Adults chew completely via the leaf, typically in a shothole sample. Larvae skeletonize the leaf floor, inflicting broken foliage to show brown to whitish. Elm leaf beetles, when plentiful, can completely defoliate massive elm bushes, which eliminates summer time shade and reduces the aesthetic worth of bushes. Repeated, intensive defoliation weakens elms, inflicting bushes to say no. Nevertheless, the elm leaf beetle has not been a major, widespread downside in California because the 1990s.
It’s important to accurately determine the reason for broken elm leaves earlier than taking administration motion. European flea weevil, Orchestes alni, additionally chews holes in elm leaves and causes elms to defoliate. This launched beetle has develop into a severe elm pest within the japanese United States, however at present doesn’t happen in California. Additionally from a distance, foliage severely chewed by beetles resembles the browning and dieback attributable to Dutch elm illness fungi, Ophiostoma (=Ceratocystis) ulmi and O. novo-ulmi. Report any suspected Dutch elm illness, European flea weevil, or different new pests to the native county agricultural commissioner.
The place the elm leaf beetle is an issue, handle it with an built-in program that comes with good cultural practices, conservation of pure enemies, common monitoring, and the usage of less-persistent pesticides, bark banding, or systemic insecticide. Acknowledge that elm leaf beetle populations traditionally have fluctuated dramatically from yr to yr and bushes don’t warrant remedy most years. When administration is warranted, use a mix of strategies; as a result of no single motion improves the well being of elm bushes or kills 100% of the pests.
Good cultural care of bushes is an integral part of built-in pest administration. American and European elm species are tailored to summer time rainfall. Preserve tree vigor, and shield trunks and roots from harm, by offering acceptable irrigation in areas with summer time drought. Examine for useless or dying branches and promptly take away them. Dying branches pose a limb drop (failure) hazard and supply habitat for bark beetles, Scolytus multistriatus and S. schevyrewi, which vector the Dutch elm illness fungi. Keep away from pointless pruning; and when pruning make cuts correctly, ideally throughout late fall and winter and when bushes are younger.
Select species or cultivars that resist each Dutch elm illness and elm leaf beetle when planting (Desk 1). Pest-resistant elms embody Accolade, Emerald Sunshine, Frontier, Prospector, and most Chinese language elms, besides Dynasty.
Management Motion Pointers
Wholesome elm bushes can tolerate substantial harm to leaves; complete defoliation could have little long-term impact on wholesome elms, particularly if leaf harm happens late within the season. Steered tips are to take motion when wanted to forestall larger than 40% defoliation (portion of leaf space chewed or leaves dropped prematurely); or if harm is much less tolerable or occurring earlier within the rising season, a remedy threshold of 20% defoliation could also be used. For added info on methods to predict the quantity of defoliation from every beetle technology seek advice from the 1998 publication by Dahlsten and others listed in References.
Timing of motion varies based on the management strategies and scenario. To keep away from unacceptable defoliation, when utilizing strategies that kill a smaller proportion of the pests or take longer to offer management permitting beetles to proceed to feed and harm leaves, take motion prior to you’d when utilizing faster-acting strategies.
Decide the necessity and efficient timing for any pesticide utility by visually inspecting leaves at about weekly intervals starting in spring when the primary technology of eggs and larvae are anticipated. Look ahead to the looks of clusters of yellowish to grey eggs and caterpillar-like larvae. The calendar date of peak abundance and harm varies vastly from yr to yr relying on spring temperatures. If beetles are too plentiful, use the warmth accumulation methodology mentioned in Diploma-Day Monitoring to find out the optimum time to examine foliage and to precisely time insecticide utility.
In case you plan to spray foliage or apply systemic insecticide to trunks, make the appliance when first- and second-instar (small) larvae are plentiful. With bark banding mentioned under, band as quickly as third-instar (bigger) larvae are noticed on leaves.
In case you drench or inject soil with a root-absorbed, systemic insecticide, the best utility time is spring when elm bushes flush new leaves or shortly after leaf flush. The time for motion is earlier than you realize positively whether or not beetles will develop into plentiful sufficient to warrant this preventive utility.
Typically, insecticide utility is unlikely to be warranted if:
- beetles and harm had been low throughout late summer time the earlier yr;
- systemic insecticide was correctly utilized the earlier rising season; or
- the winter was comparatively heat or moist or each, as a result of this climate apparently causes extra “hibernating” beetles to die earlier than elm leaves seem in spring.
If any of the above circumstances are true, keep away from insecticide utility until monitoring of crops reveals that elm leaf beetles are current and excessively plentiful.
Monitor temperatures to find out the optimum time to examine elm leaves and (if beetles are too plentiful) apply insecticide. Typically the upper the temperature, the earlier beetles and harm seem within the spring. When spring temperatures are cooler, elm leaf beetles seem later as a result of they don’t feed, develop, or reproduce under a “threshold temperature” of about 52°F.
To foretell the height abundance of every elm leaf beetle life stage, temperatures are monitored in items referred to as degree-days. One degree-day is 1 diploma above the insect’s decrease threshold temperature maintained for a full day. For the elm leaf beetle, degree-days above 52°F are accrued for every season starting March 1. The primary- and second-instar larvae of first-generation elm leaf beetles are most plentiful at about 700 degree-days above 52°F accrued from March 1. If populations are excessive and harm is anticipated, foliar insecticide spray or trunk spray or injection of systemic insecticide at about 700 degree-days will catch prone larvae at their biggest abundance.
Elm leaf beetle improvement can simply be predicted utilizing the point-and-click, degree-day calculator on-line. In case you handle massive numbers of elms, you may additional enhance your remedy through the use of degree-days together with egg presence-absence sampling, as defined within the 1993 publication by Dahlsten and others listed in References.
Elm leaf beetle populations are normally low not less than partly due to organic management by native predators and launched parasites. Predators of the elm leaf beetle embody sure bugs, earwigs, lacewing larvae, and predaceous floor beetles. The best to acknowledge parasite is a small black tachinid fly, Erynniopsis antennata. After Erynniopsis larvae feed inside and kill beetle larvae, the parasite’s 1/5 inch lengthy, black to reddish pupae could be seen on the tree base among the many yellowish, unparasitized beetle pupae. For extra pictures of this helpful fly, see the Pure Enemies Gallery.
Adults of a tiny wasp, Oomyzus gallerucae (Eulophidae), feed on elm leaf beetle eggs; and the parasite’s larvae feed inside eggs. The Oomyzus grownup leaves a spherical gap when it emerges from beetle eggs, which stay golden. When unparasitized and a beetle larva has emerged, the egg shell is whitish with a ragged gap. One other tiny eulophid wasp that kills beetle pupae, Baryscapus brevistigma, leaves a number of small spherical holes within the pupae and emerges from across the tree base.
Preserve these parasites and predators by avoiding foliar functions of residual (long-lasting), broad-spectrum pesticides. To acquire most advantages from organic management, decrease pesticide utility, use less-persistent merchandise, or apply insecticide as a bark band in an built-in program.
The place elm leaf beetle harm is anticipated to be insupportable, chemical controls embody:
- foliar spraying a nonresidual (nonpersistent) contact insecticide or a short-residual, translaminar insecticide
- bark banding, spraying bark with a residual, contact insecticide
- systemic insecticide, which could be utilized varied methods
An expert applicator have to be employed to make use of sure strategies.
Monitor beetle abundance and harm, as mentioned above, to find out remedy want, alternative of methodology, and timing. Apply insecticide solely when beetles are current or anticipated to develop into too plentiful. Pesticides can have unintended results, comparable to contaminating water, poisoning pure enemies and pollinators, and inflicting secondary pest outbreaks. Fully learn and observe the product label directions for the secure and efficient use of the insecticide.
Nonresidual, Contact Pesticides
The place elm foliage could be totally sprayed, nonresidual, contact pesticides can present management. These could be helpful on small bushes, to complement bark banding (mentioned under), in the course of the first yr of remedy and when early-season beetle populations are excessive. Merchandise embody azadirachtin (AzaMax, Safer Model BioNeem), neem oil (Inexperienced Mild Neem, Schultz Backyard Protected Model Neem), narrow-range oil (Bonide Horticultural Oil, Monterey Horticultural Oil), and pyrethrins, which many merchandise mix with piperonyl butoxide (Ace Flower & Vegetable Insect Spray, Backyard Tech Fear Free Model Focus).
These pesticides have low toxicity to individuals and pets and comparatively little antagonistic affect on pollinators and pure enemies. To acquire ample management, spray should totally cowl the underside of infested leaves; and sometimes, foliage have to be sprayed greater than as soon as per season.
Spinosad is foliar sprayed, absorbed brief distances into plant tissue (it has translaminar exercise), and persists about 1 week. It may be simpler to acquire management utilizing spinosad compared with the merchandise above. Spinosad (Captain Jack’s Deadbug Brew, Preserve, Monterey Backyard Insect Spray) could be poisonous to sure pure enemies (e.g., predatory mites, syrphid fly larvae) and bees when sprayed and for about 1 day afterward. Don’t apply spinosad to crops which can be flowering.
Spraying a small space across the tree trunk with a residual, contact insecticide kills larvae after they cross the handled bark and migrate down after feeding within the cover. Bark banding reduces harm by later beetle generations by decreasing the variety of elm leaf beetles that pupate and emerge as adults, particularly when carried out to all close by elms.
Bark banding alone is not going to present passable management in lots of conditions, particularly if just one or just a few bushes are handled. Anticipate good management in the course of the first season of bark banding on Siberian elms (Ulmus pumila). When banding extra prone species comparable to English and Scotch elms, anticipate little or no management the primary yr if beetles are plentiful in the course of the first technology; banding all close by elms for a number of consecutive years can present management after the primary yr of remedy.
To bark band spray a a number of toes broad space encircling the trunk across the first foremost department crotch. Carbaryl (Sevin) could be utilized on the price labeled for bark beetles (about 2% lively ingredient). Pyrethroids (e.g., fluvalinate) labeled for utility to bark additionally present management. Bark banding could have to be carried out by a licensed pesticide applicator, as a result of efficient merchandise usually aren’t obtainable for house customers. Don’t use merchandise labeled just for foliar utility. The product is not going to be efficient for trunk banding until the label contains instructions for utility to bark.
Examine foliage usually and spray bark when mature larvae are first noticed on leaves. For extra correct timing, accumulate degree-days and spray the trunk when about 700 degree-days (above 52°F) have accrued from March 1. A single utility of carbaryl to the bark every spring can kill most larvae that crawl over all of it season lengthy. To find out if the bark band continues to be efficient, usually examine across the base of bushes all through the season. If many beetles have modified from greenish prepupae (the stage killed by banding) to yellowish pupae (unaffected beetles), a second utility could also be warranted.
Systemic pesticides are absorbed by one plant half (e.g., trunks or roots) and moved (translocated) to leaves or different plant components. Compared with systemics which can be sprayed onto foliage, merchandise labeled for soil drench or injection or for trunk injection or spraying decrease environmental contamination and could also be more practical. Trunk utility of systemic insecticide can present comparatively fast management. There’s a longer time delay between soil utility and insecticide motion. Most makes use of require hiring knowledgeable pesticide applicator. Some home-use merchandise can simply be drenched into soil across the tree trunk utilizing the mix-and-pour methodology.
Systemic neonicotinoids embody dinotefuran (Safari) and imidacloprid (Bayer Superior Tree & Shrub Insect Management, Benefit). Correctly utilized, one utility can present season-long management. The insect development regulator abamectin (Agri-Mek) and the organophosphate acephate (Lilly Miller Prepared-to-Use Systemic, Orthene) are different obtainable systemic pesticides.
Some systemic pesticides may cause spider mite outbreaks. Foliar sprays of them could be poisonous to helpful bugs that contact spray or handled leaves. Systemics can translocate into flowers and have antagonistic results on pure enemies and pollinators that feed on nectar and pollen. Nevertheless, elms are wind pollinated and most elm species flower earlier than leaves flush and earlier than the beneficial instances of insecticide utility.
Except the product label directs in any other case, don’t apply systemic pesticides to crops throughout flowering or shortly earlier than flowering, wait till after crops have accomplished their seasonal flowering. With soil utility, when potential, wait till close by crops even have accomplished flowering as their roots could take up a number of the soil-applied insecticide.
If making use of systemic insecticide, use soil utility or a trunk spray each time potential. It’s tough to repeatedly place insecticide on the correct depth with systemic injection and implants, and these strategies injure bushes and might unfold plant pathogens on contaminated instruments. When injecting or implanting a number of bushes, earlier than shifting to work on every new tree, scrub any plant sap from instruments or tools that penetrate bushes and disinfect instruments with a registered disinfectant (e.g., bleach). No less than 1 to 2 minutes of disinfectant contact time between contaminated makes use of is mostly required. Take into account rotating work amongst a number of instruments and use a freshly disinfected device whereas essentially the most lately used instruments are being soaked in disinfectant. Keep away from strategies that trigger massive wounds, comparable to implants positioned in holes drilled in trunks. Don’t implant or inject roots or trunks greater than yearly.
Residual, Foliar Sprays
Foliar sprays of broad-spectrum pesticides with residues that may persist for weeks aren’t beneficial for elm leaf beetle management. Merchandise to keep away from embody carbamates (carbaryl or Sevin), nonsystemic organophosphates (malathion), and pyrethroids (fluvalinate, permethrin). These are extremely poisonous to pure enemies and pollinators and might trigger spider mite outbreaks. As a result of their use in landscapes and gardens can run or wash off into storm drains and contaminate municipal wastewater, these pesticides are being present in floor water and are adversely affecting nontarget, aquatic organisms.
|Elm Frequent Title||Scientific Title||ELB||DED|
|Emerald Sunshine||Ulmus propinqua3||R||R|
|Patriot||(U. glabra X U. carpinifolia X
U. pumila) X U. wilsoniana
|Prospector||U. wilsoniana choice||R||R|
|Frontier||U. carpinifolia X U. parvifolia||R||MR|
|Morton Accolade||U. japonica X U. wilsoniana3||R||MR|
|American New Horizon||U. americana choice||R||S|
|Homestead||U. glabra X U. carpinifolia X U. pumila||R||S|
|Morton Shiny Triumph||U. pumila X U. japonica X U.?3||R||S|
|New Horizon||U. pumila X U. japonica3||R||S|
|Morton Plainsman Vanguard1||U. pumila X U. japonica3||R||HS|
|Morton Pink Tip Danada Appeal||U. japonica X U. wilsoniana3||R||HS|
|Morton Stalwart Commendation||U. carpinifolia X U. pumila X U.?3||R||HS|
|Pioneer1||U. glabra X U. carpinifolia||R||HS|
|American Valley Forge1||U. americana choice||MR||R|
|Chinese language2||U. parvifolia||MR||R|
|Dynasty Chinese language2||U. parvifolia choice||MR||HS|
WARNING ON THE USE OF PESTICIDES
Dahlsten, D. L., D. L. Rowney, and A. B. Lawson. 1998. IPM helps management elm leaf beetle. Calif. Agric. 52(2):18–24. Univ. Calif. Agric. Nat. Res.
Dahlsten, D. L., S. M. Tait, D. L. Rowney, and B. J. Gingg. 1993. A monitoring system and growing ecologically sound remedies for elm leaf beetle. J. Arboriculture 19(4):181–186.
Dreistadt, S. H., J. Okay. Clark, and M. L. Flint. 2004. Pests of Panorama Bushes and Shrubs: An Built-in Pest Administration Information. 2nd ed. Oakland: Univ. Calif. Agric. Nat. Res. Publ. 3359.
Dreistadt, S. H., D. L. Dahlsten, D. L. Rowney, S. M. Tait, G. Y. Yokota, and W. A. Copper. 1991. Therapy of harmful elm leaf beetle must be timed by temperature monitoring. Calif. Agric. 45(2):23–25. Univ. Calif. Agric. Nat. Res.
McPherson, G., L. Costello, J. Harding, S. Dreistadt, M. L. Flint, and S. Mezger. 2009. Nationwide elm trial: Preliminary report from Northern California . Western Arborist. Fall 2009:32–36.
Pest Notes: Elm Leaf Beetle
UC ANR Publication 7403
Authors: S. H. Dreistadt, UC IPM Program, UC Davis; and A. B. Lawson, Entomology, California State College, Fresno.
Produced by College of California Statewide IPM Program
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