The
elm leaf beetle, Pyrrhalta luteola, is about 3/16 inch long with darker
outer margins of the wings and several black spots on the head and thorax. Eggs
are about 1/32 inch long and are yellow and spindle-shaped. The newly hatched
larva is nearly black. Larger larvae are yellow with black bumps. Full-grown
larvae are yellow with black stripes along each side. Larvae have a proleg at
the rear used for walking. Elm leaf beetle pupae are yellow to bright orange
and are usually found in litter on the ground.
The
Larger elm leaf beetle, Monocesta coryli, has two large spots
that may join at the hind area of the wings. The
larvae are brown-orange and lack the stripes along the sides. It is less
common, but occasional outbreaks are reported.
Biology
The elm leaf beetle was introduced from Europe in 1838 and is now found throughout
the United States. Elm leaf beetles feed on all elms but tend to prefer English
elms. Damage is most noticeable in landscape trees. The elm leaf beetle is consider
the most serious elm defoliator in the United States. Larvae skeletonize leaves
which then turn brown and may defoliate prematurely. Adults chew irregular holes
in the leaves. Heavily infested trees may be weakened or even killed after repeated
attacks. In fall, adults may be a nuisance as they crawl into buildings seeking
an overwintering site.
Elm leaf beetles overwinter as adults. As the buds on elms start to swell in spring, the beetles begin to emerge. Females begin laying eggs in late May and over the next several weeks, deposit 400 to 800 eggs each in clusters of two or three rows. Eggs are usually place near the midrib on the underside of leaves. About a week later, they hatch into tiny larvae which skeletonize the leaves by feeding on the lower surface but leaving a thin layer of the upper surface intact. The larvae mature in two or three weeks at which time they drop to the ground to pupate under litter or some other shelter near the base of the tree. A new generation of adults emerges in about ten days. Many of the beetles which emerge during the summer months seek places for hibernation early in the season. This movement toward shelter continues until cool weather.
For optimum control, trees should be sprayed when the leaves are about
3/4 grown while the adults are feeding and laying eggs. A second application
three weeks later will control larvae. Good coverage of the underside of
the leaves is essential for effective control. The pesticides below are
labeled for elm leaf beetle control.
| Pesticide (Trade Name) | Formulation | Remarks |
| *acephate (Orthene, Orthenex) | 9.4 % emulsifiable concentrate | 3 tablespoons per gallon of water. |
| *Bacillus thuringiensis var. San Diego (M-One) | 5.6 water dispersable liquid | 2 to 2 1/2 quarts per 100 gallons of water |
| bifenthrin (Talstar) | 10 % wettable powder | 1 to 5 teaspoons per gallon or 6.4 to 32 ounces per 100 gallons of water |
| *carbaryl (Sevin) | 21.3 % liquid flowable | 4 teaspoons per gallon of water. |
| carbaryl (Sevin) | 50 % wettable powder | 4 pounds per 100 gallons of water |
| cyfluthrin (Decathlon) | 20 % wettable powder | 9 tablespoons per 100 gallons of water. |
| dinotefuran (Safari) | foliar spray or soil drench systemic | |
| *fluvalinate (Mavrik Aquaflo) | 23 % aquaeous flowable | 1/8 to 5/8 teaspoon per gallon of water. |
| *imidacloprid (Merit) | 75 % wettable powder | follow label directions |
*Suitable for home use. Some lawn and garden pesticides containing cyfluthrin and permethrin are also available.
Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.
Recommendations for the use of chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage and examine a current product label before applying any chemical. For assistance contact an agent of North Carolina Cooperative Extension in your county.
© 2001 NC Cooperative Extension
Prepared by: James R. Baker, Extension Entomologist Emeritus
ENT/ort-85 January 1995 (Revised) 2000
Web page last reviewed January, 2011 by the webperson.