Defoliation of Live Oak Trees by
the Oak Leaf Roller and a Closely Related Moth
The oak leaf roller, Archips semiferana, and an associated species, Sparganothis pettitana, is increasing in importance in the Hill Country and South Texas. Damaging populations have occurred in Fredericksburg, Kerrville, Boerne, New Braunfels, San Antonio, Floresville and Goliad.
The oak leaf roller and Sparganothis pettitana are small moths that undergo one generation each year. Eggs from these moths are laid on twig tips and buds of several types of trees during May. Eggs remain on the buds or twigs for about ten months and begin to hatch in mid-March. Newly hatched caterpillars feed on tender new growth on the trees and continue to feed until late April. Trees heavily infested are usually defoliated by mid to late April, at which time the fully grown caterpillars form the pupa stage on twig tips, in bark crevices, or on weeds growing near infested trees. Moths begin to emerge from the pupal stage (cocoon) about the first of May and begin to lay eggs on twigs of oak, hackberry, pecan and walnut trees. These eggs will remain dormant until next March, thus completing the one year life cycle.
Description of the Moths
The oak leaf roller, Archips semiferana, is a small moth about 1/2 inch long. The basic color is brown mottled with dark brown markings. Sparganothis pettitana (no common name) is lemon yellow and varies from 1/2 to 3/4 inch in length.
OAK LEAFROLLER larvae.
Damage to Trees
When any tree is defoliated during the growing season, serious damage can occur. Green leaves manufacture sugar that is later converted into other carbohydrates that allow the tree to grow, thus keeping the plant healthy. When trees are defoliated, manufacture of sugar is essentially stopped and growth of the trees does not occur.
Trees can maintain life for short periods by using their reserve food supply but are more susceptible to disease and insect attack. Complete defoliation year after year could result in tree death, especially under drought conditions.
Oak leaf roller caterpillars suspend from trees on silken strands that can cover tree trunks, shrubs, grass and become a nuisance by dropping onto people in the yard. The problem is so pronounced that by mid-April, many Hill Country residents abandon patios due to hundreds of caterpillars.
Natural or Biological Control
Insecticidal control of the oak leaf roller may be necessary on valuable yard or orchard trees (pecan) but is not feasible for oak trees throughout the Hill Country. There are several types of wasps that attack and kill the oak leaf roller but may not occurred; in sufficient numbers to curtail an outbreak.
Certain birds such as mockingbirds were observed feeding on the caterpillar stage but parasitic wasps appear to be the best control.
Bacillus thuringiensis: If the caterpillars are too high to reach, an effective biological control agent is BTK (Bacillus thuringiensis, kurstaki strain). BTK is a naturally occurring bacterium that will attack only caterpillars. Other strains of BT will attack a variety of insects, so for caterpillar control, be sure the strain is kurstaki. The BTK bacteria will not affect humans, pets, or other organisms in the environment, so it is a non-toxic method of biological pest control. Therefore, it is very important to make sure that the problem is actually caterpillars, since BTK will not control other types of 'worms' such as sawfly larvae or leaf beetle larvae (see:
Using BT: BTK is available in dust form to be sprinkled directly on plants, or it can be mixed according to label instructions to make a foliar spray. One tablespoon of horticultural oil added to each gallon of spray will help the BT adhere to the plants. It is also available in a liquid concentrate formulation that adheres well to plants. Apply the dust or spray to both the top and undersides of leaves, as the BT will survive longer when not hit by direct sunlight. If using a dust, wet the plants before application. Apply every 10 to 14 days, and after rains, until the pest is under control. The caterpillars must actually consume the BT as they are feeding on foliage in order for it to be effective.
Spinosad: is a very effective caterpillar control, and is virtually non-toxic to humans, pets, and wildlife. It has little impact on beneficial insects, bees, or insects that do not eat plant leaves. Spinosad is derived from a soil bacterium discovered in an abandoned rum distillery by a vacationing scientist in 1982.
What to Look For
The oak leaf roller occurred in outbreaknumbers in 1988, 1989 and 1990 but has not been a serious pest in 1991 and 1992. Valuable landscape trees should be watched during late March and if significant feeding damage is occurring, insecticidal sprays containing carbaryl (Sevin®) or the biological caterpillar sprays that contain Bacillus thuringiensis var. kurstaki may be applied for control.
Oak trees that received severe leaf damage in the past should be fertilized and watered regularly to restore vigor. Select a balanced fertilizer and apply at the rate of one pound per diameter inch of the trunk. Fertilizers should be applied in a circular pattern under the drip line of the tree. The drip line is the area beneath outer most limb area, away from the trunk. A second application of fertilizer should be applied 6 to 8 weeks later for best results. The second application should be ammonium sulfate (21-0-0), applied at the same rate eg., one pound per diameter inch of trunk.
Cankerworm - Oakworms - Tent Caterpillars - Bag Worms - Oak Leaftiers
The information given herein is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by the Cooperative Extension Service is implied.