Cypress tipminer—Argyresthia cupressella
Cypress tipminer is the most common of several Argyresthia spp. that tunnel in foliage of Cupressaceae. The larvae (caterpillars) of this moth (Argyresthiidae, or Yponomeutidae) feed mostly along the coast on arborvitae, coast redwood, cypress, and juniper.
Cypress tipminer damage resembles that of certain webworms including the cypress leaftier, cypress webber, and juniper webworm and these species can occur together. Cypress tipminer damage may also be confused with foliage discoloring and twig dieback caused by juniper twig girdler and minute cypress scale.
The larvae of cypress tipminer occur inside foliage and twigs and grow up to 1/4 inch long. They are yellowish green to pinkish with a darker head and prothoracic shield (area on top the first abdominal segment). Pupae occur in white, silken cocoons between twiglets. The adult cypress tipminer is a silvery, brown and whitish moth with a wingspan of about 1/3 inch.
Cypress tipminer has four stages of development—egg, larva, pupa, and adult. Adults can be found mostly from March through May in Southern California and during April and May in Northern California. Females lay flattened, ovoid eggs on green tips. The eggs soon hatch and larvae chew into branch tips and terminal foliage where they feed during summer through winter.
During winter to spring, mature larvae exit mines to pupate on twiglets. Adults soon emerge and mate and the females lay eggs on hosts. There is one generation per year.
Larvae chew inside foliage and small twigs, causing foliage to turn yellow, then brown and die. High populations of the tipminer can cause most of the plant's foliage to discolor. However, feeding damage is commonly limited to scattered, small areas of a plant.
Foliage infested with cypress tipminer turns yellow in early winter and brown by late winter or early spring. The green color of plants is restored by new growth in the spring and summer. Although unsightly, even severe infestations do not kill plants. When growing in a nursery the discolored plants become unmarketable.
Where foliage damage from cypress tipminer cannot be tolerated, consider replacing plants especially susceptible to this pest. High populations of cypress tipminers and their damage that are intolerable can be reduced by applying a systemic insecticide (e.g., imidacloprid) in mid to late winter or spraying a broad-spectrum, residual (persistent) insecticide (e.g., carbaryl) when adult moths are active. This reduces foliage browning the next year.
If hosts may be sprayed, examine foliage tips for the cocoons beginning in late winter. When cocoons appear, vigorously shake branches and watch to see if tiny, silvery moths fly from the foliage. One application to foliage can be made when a large number of tip moths appear, between March and May.
For more information, consult Cypress Tip Moth from Oregon State University and Insects Affecting Ornamental Conifers in Southern California from the University of California.
Adapted from Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide, University of California Statewide Integrated Pest Management Program (UC IPM).
Foliage browning from cypress tipminer feeding.
Larval emergence hole (center right) and damage.
Last instar cypress tipminers.
Adult (center right), cocoon, and damage of cypress tipminer.
Relative size of adult cypress tipminer.