A3178 Deciduous trees eciduous tree disorder: Cankerworms DP.J. PELLITTERI, D.L. MAHR, and D.J. HALL Severe, early season defoliation Symptoms and effects Life cycle of several hardwood tree species may When the larvae are small, they Although the spring and fall be caused by cankerworms. There are feed only on the softer tissues of the cankerworms do the same type of two important species throughout leaves, leaving the main veins and damage, at about the same time of Wisconsin: the spring cankerworm leaf membrane intact. This type of year, their appearance and life cycles ( vernata) and the fall feeding, called “skeletonizing,” differ somewhat. cankerworm (Alsophila pometaria), occurs in late April and early May, Spring cankerworm named for the times of the year that and is the first indication of damage. Spring cankerworms the adults appear. Usually natural As the larvae grow they begin to overwinter in the factors such as weather, predators consume all leaf tissue except the larval stage in cells and parasitic keep canker- major veins. When a population is in the soil at the tree worms in check. However, at certain large, partial or complete tree defolia- base. They pupate in times the environment becomes very tion results. The larvae finish feeding the soil in very early favorable for one or both species of in early June. Because most trees still spring, and the adults emerge shortly cankerworms, and an outbreak are growing actively at this time, they after the frost leaves the soil. Eggs are occurs. Outbreaks usually last from a continue to produce new foliage. laid in March and April in loose clus- few to several years before natural Even after complete defoliation, trees ters of 100 or more eggs. These clus- controls again become effective. usually refoliate within 2–3 weeks. ters are deposited under loose bark Preferred host plants include However, foliage is more sparse than or in bark crevices. Hatching occurs apple, crabapple, and . However, if defoliation had not occurred. in early May and larvae are fully many other deciduous trees, including trees may die after 2–3 grown by early June. After they finish ash, cherry, hickory, maple, and oak, years of severe defoliation. Most feeding they drop to the ground and among others, are also attacked. other species of trees will not die but enter the soil, remaining inactive may be weakened enough to be until the following spring. attacked by When larvae hatch, they are 1 disease slightly less than ⁄4 inch in length. organisms or When fully grown, they are about other insects. 1 inch long. The larvae are typical The growth “inchworms,” walking in a looping of young fashion. Besides the three pairs of trees may be true legs just behind the head, there retarded due is a pair of “prolegs” on the sixth to canker- abdominal segment and another on worm attack. the last segment. They vary greatly in The larvae color, from yellowish green, to Cankerworm larva and feeding damage to oak leaf. can also reddish, brown or even almost black. become a The adult stage is a . The male is nuisance because of their large brownish-gray, with a wingspan of 7 1 numbers and the abundant waste ⁄8–1 ⁄4 inch. The females are mottled, material and silk they produce. whitish and brown or black, and do not have wings. DECIDUOUS TREE DISORDER: CANKERWORMS

Fall cankerworm when these natural controls are inef- as soon as possible after the eggs have The fall cankerworm fective and the environment favors hatched in spring. These materials overwinters in the the cankerworms. contain a bacterium which causes the egg stage. The eggs Cultural caterpillars to die from a disease. are laid in compact To lay eggs, the flightless females They are safe to use and have activity clusters of uniform must crawl from the soil up into the only against caterpillars, thereby pro- rows. Clusters con- tree. By placing a sticky band low on tecting most of the beneficial taining about 100 eggs are usually the tree trunk, females will be unable species. Brand names include Dipel, located on the smaller twigs and to crawl into the tree to lay eggs. Thuricide, Sok-Bt, and Bactur. branches. Larvae hatch in late April to Several brands of sticky materials Several chemical insecticides are early May, and are fully grown by mid- designed for this purpose are avail- registered for cankerworm control. June. When finished feeding, they drop able from garden centers and hard- These include acephate (Orthene), to the ground and enter the soil to ware stores. However, these materials carbaryl (Sevin), methoxychlor, and pupate. Adults emerge in November, may injure thin barked trees. Wrap phosmet (Imidan). Apply chemical usually following some freezing such trees with a band of fabric, and insecticides as soon as possible after weather, and mate, lay eggs and die. then apply the sticky material to the spring egg hatch. Specialized spray 1 The larvae are about ⁄4 inch long fabric. Leave no gaps in the band of equipment is usually necessary for at hatching, but grow to slightly over sticky material. thorough coverage of large trees, and it 1 inch. Fully grown larvae vary in color Maintain sticky bands on the tree may be necessary to consult a commer- from pale green to dark brownish from mid-March to mid-May for cial tree care specialist. Remember, the green. There is a darker stripe down spring cankerworm, and from mid- health of many mature trees usually the middle of the back. Unlike the October to mid-December for fall will not be affected permanently by spring cankerworm, which has two cankerworm. one or two defoliations. In such cases, pairs of prolegs, the fall cankerworm Sticky bands do not always elimi- chemical control is suggested only if has three pairs. The adult male is nate cankerworms from banded trees. the insects are creating a nuisance. brownish gray with a wingspan of The very young cankerworm larvae 3 1–1 ⁄8 inch. The female is a dark, shiny can be blown from adjacent trees or References to products in this publication gray and wingless. are for your convenience and are not an woodlots. However, in some situa- endorsement or criticism of one product Control tions these sticky bands may provide over other similar products. You are sufficient control so that chemical con- responsible for using chemicals according Natural to the manufacturer’s current label direc- trols are not necessary. Populations are generally tions. Follow directions exactly to protect Chemical the environment and people from chemical checked by various natural factors Microbial insecticides containing exposure. including adverse weather; bird, Bacillus thuringiensis effectively reduce rodent, and insect predators; and par- cankerworm populations. Apply them asitic insects. Outbreaks occur only

©1997 University of Wisconsin-System Board of Regents and University of Wisconsin-Extension, Cooperative Extension Authors: P.J. Pellitteri is distinguished outreach specialist of entomology and D.L. Mahr is professor of entomology, College of Agricultural and Life Sciences, University of Wisconsin-Madison and University of Wisconsin-Extension, Cooperative Extension. D.J. Hall is forest entomologist, Forest Pest Control Unit, Wisconsin Department of Natural Resources. Produced by Cooperative Extension Publications, University of Wisconsin-Extension. University of Wisconsin-Extension, Cooperative Extension, in cooperation with the U.S. Department of Agriculture and Wisconsin counties, publishes this information to further the purpose of the May 8 and June 30, 1914 Acts of Congress; and provides equal opportunities and affirmative action in employment and programming. If you need this material in an alterna- tive format, contact the Office of Equal Opportunity and Diversity Programs or call Cooperative Extension Publications at 608-262-8076. This publication is available from your Wisconsin county Extension office or from Cooperative Extension Publications. To order, call toll free 877-WIS-PUBS (947-7827) or visit cecommerce.uwex.edu. A3178 Deciduous Tree Disorder: Cankerworms SR-09-97