Cypress Tipminer

Cypress tipminer larvae (caterpillars) are the most common of several Argyresthia spp. (family Argyresthiidae or Yponomeutidae) that tunnel in foliage of Cupressaceae, mostly in coastal growing areas. Hosts include arborvitae, coast redwood, cypress, and especially Thuja occidentalis and certain junipers. Tipminer larvae chew and feed inside branch tips and terminal foliage during summer through winter. First instars hatch from eggs in late winter through spring and feed briefly exposed on foliage as they chew a tunnel into foliage. Larvae grow up to 1/4 inch long and are yellowish green to pinkish with a darker head and prothoracic shield (area on top the first thoracic segment). Mature larvae exit mines in late winter or early spring then pupate in white, silken cocoons between twiglets.

The adult appears silvery (shiny) to the naked eye. It is brown and whitish with a wingspan of about 1/3 inch. Adults occur mostly from March through May in Southern California and during April and May in Northern California. After mating, females lay flattened, ovoid eggs on green tips. The tiny eggs hatch soon after they are laid. There is one generation per year.

Foliage of Cupressaceae infested with cypress tipminer turns yellow in early winter, then brown by late winter or early spring. Feeding damage is commonly limited to scattered, small areas of a plant. However, abundant tipminers can cause most of a plant's foliage to discolor. The green color is restored by new growth in the spring and summer, and even severe infestations do not kill plants. However, tipminer presence in a nursery causes plants to be obviously discolored, unsightly, and unmarketable.

Cultural controls and insecticide application are key management practices for this pest. The importance of natural enemies (parasites, predators, and pathogens) is unknown for cypress tipminer.

Where cypress tipminer has been a problem, consider avoiding production of highly susceptible hosts (e.g., Thuja occidentalis); instead, grow less susceptible cultivars and species. Hosts least susceptible to cypress tipminer include Juniperus chinensis 'Kaizuka,' J. chinensis var. sargentii 'Glauca,' J. scopulorum 'Erecta Glauca,' and Thuja plicata. Grow hosts within well-maintained screen structures or hoop houses to exclude the egg-laying moths, which are active mostly at night. To reduce moth attraction to growing areas consider using motion-activated security lights instead of always-on night lighting.

Cultural controls are organically acceptable management methods. The microbial insecticides Bacillus thuringiensis ssp. aizawai or ssp. kurstaki, and certain spinosad formulations (Entrust Naturalyte, Entrust SC) are acceptable for organic production.

Where cypress tipminer has been a problem, examine host foliage tips for whitish cocoons about 1/5 inch long beginning in mid- to late winter. When cocoons appear, vigorously shake branches and watch for tiny, silvery moths that fly from the foliage. If it is uncertain whether the tiny moths dislodged are those of cypress tipminer several can be collected, such as with an aspirator, and taken to the local office of the county department of agriculture or University of California Cooperative Extension for identification.

One thorough foliar spray of a broad-spectrum, persistent insecticide can be made when a noticeable number of tip moths (adults) are present, between March and May. Bacillus thuringiensis is highly effective against first instars. Because eggs do not all hatch at the same time, make several Bt applications at about weekly intervals during late winter through spring to control larvae before they bore into plant tissue.

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