Zimmerman Pine Moth

Zimmerman Pine Moth Adult Zimmerman pine moths are midsized with gray and red-brown wings, marked with zigzag lines. Larvae are generally dirty white to light grey and up to one inch long. They can only be found in pitch masses, under bark or in new shoots.

Zimmerman pine moth larvae tunnel into new growth causing shoot dieback, or into whorl areas causing masses of pitch to form at the wound site. Repeated attacks by the larvae cause a weakening at the area of the infestation and make the branches and trunk susceptible to breakage.

Zimmerman pine moth has long been a pest of pines in the Midwest but has become increasingly noticeable in the past few years. The larva of this moth species is a borer that attacks pine tree trunks and lateral branches. Trees rarely are killed by this insect but they are disfigured as branches die. Borer damage can weaken trees and cause trunks or branches to break off during heavy ice, snow or wind.

Actively feeding larvae are found under the bark and reach lengths of 18-25 mm at maturity. Their color varies from dirty white to pink or green, and small black spots can easily be seen at the base of some dorsal setae. Field identification generally depends upon discovery of larvae in galleries and on symptoms discussed below. Preferred hosts are Scotch and Japanese red pine though Ponderosa, eastern white, Jack, Mugo, red and Austrian pines can be hosts.

Life Cycle: Most Zimmerman pine moth eggs are deposited on the bark of the main trunk shortly after adults emerge in late summer. Eggs are ovoid with a wrinkled surface. Initially creamy white, eggs darken to a deep reddish brown before hatching. After leaving the eggs, newly hatched larvae quickly move to nearby pro¬tected sites under bark scales or in crevices below a main lateral branch. They do not feed but immediately spin a silken chamber, or hibernaculum, in which they will overwinter.

In mid-April, when Scotch pine terminal growth is starting, the overwintering larvae leave the hibernaculi. They begin to feed on the bark, chewing into the inner bark. Favored points of entry appear to be succulent scar tissue around wounds and the junction of a lateral branch and main stem. The first indication of larval feeding is the appearance of frass, and possibly pitch, at these sites.

Zimmerman pine moth larvae mine inner bark anywhere on the main stem and may also feed inside the terminal shoots. Before pupating, mature larvae prepare their emergence sites by chewing away most of the bark from the inside. The pupal stage is complete in approximately 2-3 weeks, and adults emerge through the thin layer of outer bark left by the larvae. Frequently, empty pupal cases can be found protruding from adult emergence holes. Mating occurs shortly after adults emerge, usually during late July and August. Zimmerman pine moth has a single generation each year.

Damage : The larvae usually burrow into the trunk and branch bases around a whorl. This weakens the whorl which may break in wind storms. Most commonly, upper branches or the leader break, bend or die. Occasionally, the larvae burrow within a branch or leader, eventually killing it. This damage is sometimes confused with the pine shoot moth damage. An infestation at the base of a tree may cause the entire eliminate the possibility of training a new leader to make a saleable tree.

Look at the lateral branch attachment for popcorn like frass and pitch near the tops of the trees. On damaged trees foliage turns yellow followed by die back. Groups if dead branches at the tops of pines are an indicator.

Monitoring Check fields during the seedling stage, at thinning, and just before heading. Also, record diamondback larvae numbers when you make your twice-weekly samples for other caterpillar pests. In cabbage fields, regularly monitor wrapper leaves for damage after heading. Adult moths frequently migrate from fields being harvested or disced under, so carefully check border rows if populations were high in adjacent fields. No treatment levels have been developed for diamondback moth in California; however, treatment may be required if significant injury to growing points is occurring.

Control: Removal of Infested Stock – Early detection of an infestation may allow for removal and burning of infested stock. Heavily infested trees should also be removed and burned because they will rarely recover to become saleable trees. Check around the plantation for forest pines with infestations. If these can be removed, and since the adult moths rarely fly further than mile, reinfestation will be minimized.

Clear Cut – This pest seems to prefer trees in the four to eight foot tall category. By clear cutting a field before planting new seedling, carry over from one crop to the next can be reduced.

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