The caterpillars of the oak leaftier are often associated with the oak leafroller (Archips semiferana), discussed elsewhere in this guide. Oak leaftier caterpillars are approximately 1/2 inch long at maturity, and off-white to light green in color with a light brown head and dark colored thoracic legs (brown to black). Caterpillars hatch from eggs in approximately mid-April to early May. The earliest hatched caterpillars are capable of entering the buds of their host plants even prior to their expansion. When population outbreaks occur, it is possible that all of the buds of a tree may be killed. Any leaves that survive often expand with holes created before they even opened, damage similar to other early season feeding caterpillars like winter moth (Operophtera brumata). Caterpillars of the oak leaftier create webbing and fold leaves, which provides protection for older caterpillars that eventually feed out in the open. Once mature, the caterpillars drop from their hosts to the ground on a strand of silk, where they pupate on the ground. The adult moth of the oak leaftier emerges approximately in June and July and females lay their eggs on the twigs or bark of their hosts. Moths are approximately 15 mm long and yellow with brown markings. A single generation occurs per year.
Oak leaftier caterpillars cause damage to newly opening buds of oaks. Damage to the buds or bud death can occur. Buds that survive to expand and produce leaves may reveal leaves with many holes from early feeding. Foliage attacked by this pest can be webbed and/or folded. Damaging populations of the oak leaftier do not occur every year. However, outbreaks are possible and when they do occur, it may be in a cycle of several years. Springtime defoliation can result in worse injury to trees, as this disrupts the healthy cycle of photosynthesis and production of sugar stores for the winter.
Historically, populations of the oak leaftier were reported as heavy in 1966 in New York, New Jersey, and Connecticut. In Pennsylvania and West Virginia infestations increased in size and intensity, and the Monongahela National Forest had (at the time) 10,000 acres of oak stands suffering heavy mortality (Forest Insect Conditions in the United States, 1966, US Forest Service).
Look for damage as described above to host plant leaves in late April or early May. Canadian researchers have isolated sex pheromones that may be used with traps to monitor for the adult moths of this insect (Silk et al., 1997).
Adequate watering, particularly after any rare defoliation events caused by oak leaftier, may help trees recover from the stress caused by premature leaf loss. Other practices to promote tree health and vigor may also help reduce the impact of this insect on the tree.
At least one genus of tiny, parasitoid wasp in the family Eulophidae (Dimmockia spp.) is reported as a parasitoid of the oak leaftier (Kirkland, 2009).
Azadirachtin (NL)
Bacillus thuringiensis subsp. kurstaki (NL)
Bifenthrin (NL)
Carbaryl (L)
Chlorpyrifos (larvae) (N)
Flonicamid+cyclaniliprole (N)
Gamma-cyhalothrin (L)
Horticultural oil (eggs) (L)
Lambda-cyhalothrin (L)
Neem oil (NL)
Pyrethrin+sulfur (NL)
Pyrethrins+piperonyl butoxide (L)
Spinosad (NL)
When used in a nursery setting, chlorpyrifos is for quarantine use only.
Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.
Note: Beginning July 1, 2022, neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.