Oak Leaf Roller and Springtime Defoliation of Live Oak Trees

E-2063-04Oak Leaf Roller andSpringtime Defoliationof Live Oak TreesBastiaan “Bart” M. Drees*In early spring, manyspecies of caterpillars candefoliate oaks and othertrees. The caterpillars feed onthe early spring growth andoccasionally will eat all of thenewly emerged leaves.Two such caterpillars arethe oak leaf roller, ArchipsFig. 1. Oak leaf rollerlarva.semiferana (Walker) (Lepidoptera:Tortricidae), and anassociated species, Sparganothispettitana. These insectsoccur throughout Texas butare most destructive in theHill Country and SouthTexas. Damaging populationshave been reported in Fredericksburg,Kerrville, Boerne, New Braunfels, SanAntonio, Floresville and Goliad.These species spin silken threads from whichthey hang when dislodged from leaves, branchesor even from the trunk and nearby objects whendisturbed. Other caterpillars that dangle from silkthreads include the spring and fall cankerworms(often called "inchworms").Walking through these dangling caterpillarscan be a nuisance. By mid-April this problem maybe so common that many Hill Country residentscompletely abandon patios and other outdooractivities because of the hundreds of danglingcaterpillars.To reduce the problems caused by these caterpillars,it is helpful to know how they damagetrees and to understand their life cycle. In untreatedareas, this information may not preventencounters with dangling caterpillars. Knowingthat these caterpillars are harmless to people andanimals and that their occurrence is seasonal mayprovide some comfort. Also, wearing broadrimmedhats and long-sleeved shirts while outdoorsmay also help prevent contact with theseinsects.DamageWhen a tree is defoliated during the growingseason, it becomes stressed and occasionally seriousdamage can occur. Green leaves manufactureenergy (sugar that is later converted into othercarbohydrates) that allows the tree to grow andmaintain its natural vigor.Once a tree is defoliated, it essentially stopsmanufacturing sugar, which slows tree growth.Although deciduous trees (broad-leaved trees thatgenerally lose their leaves each winter) can producenew leaves and stay alive for short periods,this process uses up their reserve food supply.Fig. 2. Cankerworm or inchworm.*Professor and Extension Entomologist, The Texas A&M University System.

More importantly, these stressed trees aremore susceptible to attack by various diseases andinsects. Weakened trees are extremely susceptibleto wood-boring insects such as longhorn beetles,flat-headed tree borers, shot-hole borers and manyclear-winged tree borers. (For more informationon these insects, see the Texas CooperativeExtension publication B-5086, Wood-Boring Insectsof Trees and Shrubs.)If the trees are completely defoliated yearafter year, especially under the drought conditionsthat are common across Texas, they will die.Life cycleThe adult mothof the oak leafroller, Archips semiferana,is about 1/2inch long. Its wingsare mottled brownwith dark brownmarkings. Sparganothispettitana (nocommon name) haslemon yellow wingsand ranges from 1/2to 3/4 inch long.Both species undergo one generation eachFig. 3. Oak leafroller moth (left) andpupal skin (right).year. In May, moths of both species lay their eggson the twig tips and leaf buds of several differenttree species. The eggs remain on the buds or twigsfor about 10 months and begin to hatch in mid-March.Once they hatch,the caterpillars, or larvae,feed on the tendernew spring growth ofthe trees from mid-March until late April.The larvae are creamywhite to greenish andhave dark black orbrown head capsules.They develop throughseveral stages, orinstars, as they matureto about 3/4 inch long.Fig. 4. Oak leaf roller mothlarva (above) and adult (below.)Trees that are heavily infested will usually bedefoliated by mid- to late April, when the fullygrown caterpillars form the pupa stage on the tipsof twigs, in bark crevices or on weeds and otherplants growing near the infested trees.Fig. 5. Oak leaf roller, Archips semiferana (Walker) (Lepidoptera:Tortricidae) adult (left), pupal skin (center) and caterpillar(right), collected from oak trees, March 2002.At about the first of May, moths begin toemerge from the pupal stage (cocoon) and beginlaying eggs on the twigs of oak, hackberry, pecanand walnut trees. These eggs will again remaindormant until the following March, thus completingthe 1-year life cycle.ManagementFor most oak trees throughout the HillCountry, it is not feasible to use insecticides tocontrol the oak leaf roller and its related species.Often the best course of action is to simply donothing. Post oak trees have survived in South andCentral Texas without human interventionthrough time, despite periodic pest outbreaks andresulting defoliation. Caterpillar pest populationsare generally cyclic, and they rarely occur yearafter year.The oak leaf roller doeshave a few natural enemies.The best natural controlappears to be provided byseveral types of parasiticwasps that attack and kill theoak leaf rollers. However,there are seldom enough ofthese wasps to curtail an outbreak.Certain birds, includingmockingbirds, have alsobeen observed feeding on thedangling caterpillars.Fig. 6. Close-up of oakweb worm caterpillar.2

In residential situations, however, valuablelandscape or orchard trees may need to be protectedfrom caterpillar outbreaks. Valuable landscapetrees with a history of leaf roller infestationand defoliation should be watched closely frommid- to late March. If heavy leaf-feeding damageis observed, the tree leaves can be sprayed with aregistered insecticide containing either carbaryl(such as Sevin®), the insecticide that containsBacillus thuringiensis var. kurstaki, or any of severalother products labeled for control of "caterpillars"or "oakworms" on ornamental trees andshrubs.To minimize stress and to restore plant vigor,oaks or other trees that have been severely defoliatedin the past should be fertilized and wateredregularly. Choose a balanced fertilizer (one thathas equal amounts of the three major elementsnitrogen, phosphorus and potassium) and apply itat the rate of 1 pound of nitrogen (N) per diameterinch of the trunk at waist height.Apply the fertilizer in a circular pattern withinthe tree's drip line, which is the area undera tree from the trunk to the outermost limb.For best recovery of the trees, apply ammoniumsulfate (21-0-0) at the same rate 6 to 8 weeks later.AcknowledgmentsThis fact sheet was originally developed byJ. W. Stewart, Extension entomologist, and BobBailey, county Extension agent for KendallCounty, as part of the Upper Coast series, No. 21.Their publication, Defoliation of Live Oak Trees bythe Oak Leaf Roller and a Closely Related Moth, waspublished in April 1993.The author wishes to thank James Reinert,Roger Gold and Michael E. Merchant for reviewof this manuscript.Photographs and line drawings by Bastiaan"Bart" M. Drees.The information given herein is for educational purposes only. Reference to commercialproducts or trade names is made with the understanding that no discrimination is intendedand no endorsement by Texas Cooperative Extension is implied.Produced by Agricultural Communications,The Texas A&M University SystemExtension publications can be found on the Web at: http://tcebookstore.orgVisit Texas Cooperative Extension at: http://texasextension.tamu.eduEducational programs conducted by the Texas Agricultural Extension Service serve people of all ages regardless of socioeconomic level, race, color, sex, religion,handicap or national origin.Issued in furtherance of Cooperative Extension Work in Agriculture and Home Economics,Acts of Congress of May 8, 1914, as amended, andJune 30, 1914, in cooperation with the United States Department of Agriculture. Chester P. Fehlis, Director, Texas Cooperative Extension,The Texas A&M University System.3