Zimmerman pine moth larvae form frass filled pitch masses to form on trunks and branches.

Zimmerman pine moth larvae can cause branches to break out.

Larvae of Zimmerman pine moth are usually a pink to burgundy color.

Species:

Dioryctria zimmermani (Grote) is the most commonly cited species though there may be a complex of species.

Distribution:

This native pest is most commonly found in the northern half of the United States, east of the Rocky Mountains.

Hosts:

Preferred hosts are Scotch and Japanese red pine though Ponderosa, eastern white, Jack, Mugo, red and Austrian pines can be hosts.

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 tree to die. Attacks in the upper whorl usually eliminate the possibility of training a new leader to make a saleable tree.

Description and Life Cycle:

In Ohio, the adult moths emerge from in mid-August and may be active into September. They are about ½ to 5/8-inch long and have alternating zig-zag patterns of grey, brown and red. The adults fly at night. After mating, the females begin laying eggs on suitable hosts. The females lay the 1/32-inch long eggs on terminal buds, on the bark and around wounds with pitch residues. Each female may lay about 40 eggs over a two week period. The eggs hatch in 8-10 days. At this point, the scientific literature differs on the activity of newly hatched larvae. Some studies state that the larvae feed on the bases of buds and outer bark of branches and trunk. Other reports state that no feeding occurs. Overwintering larvae found in Ohio were too large to not have fed in the fall. It appears that the larvae feed before entering their overwintering sites. By the first frosts, the larvae have formed a silken tent-like hibernaculum in which they overwinter. In early spring, usually by mid-April, the larvae leave their hibernaculum and resume feeding. They may tunnel into stems or leaders or damage the phloem and cambium regions of the trunk, especially at whorls. Conspicuous resin masses with copious amounts of sawdust-like frass enclosed usually appear by late spring and early summer. The larvae, which are a deep burgundy-red color and have no hair or bristles, mature by July. The larvae spin a white silken cocoon in a previously prepared chamber in a resin mass. Upon adult emergence, the pupa wiggles to extend slightly out of the resin mass.

Control Hints:

There are several native parasites and diseases which reduce much of the population but well timed chemical sprays are the surest method of control.

Option 1: Cultural 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 ½ mile, reinfestation will be minimized.

Option 2: Cultural Control - 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.

Option 3: Chemical Control - Late Summer Sprays - As stated in the description of the life cycle, some debate exists about the feeding activity of the new larvae present in September. However, reports from Illinois and Indiana indicate that this time is the most successful window for control. Application of a long residual, borer spray insecticide should aid in reducing the numbers of larvae which may feed on bud bases or bark. Apply the materials thoroughly in mid-August. Dimethoate (nursery & Christmas tree farms only) is registered for this purpose. Astro (special formulation of Permethrin) and Onyx (& Onyx Pro - special formulations of bifenthrin) have also been shown to be effective. Thorough coverage is needed in order to achieve control.

Option 4: Chemical Control - Spring Sprays - The overwintering larvae leave their hibernaculum cocoons very early in the spring. In mid-Ohio, this should be around mid-April though emergence has been noted as early as mid-March. Apply a long lasting residual insecticide (one of the borer preventives) a week or two before the larvae are expected to become active. However, since the larvae are often under a resin mass, they may not be exposed to the common stomach insecticides. Therefore, the systemic insecticide Dimethoate (nursery & Christmas tree farms only) may be more effective in the spring. New neonicotinoid insecticides may provide control, but few studies have been performed (consider TriStar - acetimiprid or Safari - dinotefuran).