Damage

Zimmerman pine moth damages trees in two ways. They can damage terminal growth on young trees, causing them to become “fish-hooked” with yellowish-green needles. Eventually, the shoots die and turn brown. As the larvae tunnel under the bark, the areas where the larvae enter are marked by large globs of pitch. The tunneling of the larvae girdles the tree, and the branches above the tunneled area will turn brown and die. These areas are weakened, and it is at these weakened points that trees are most prone to breaking and are extremely vulnerable during strong winds.

Life Cycle

Zimmerman pine moth overwinters as tiny larvae within cocoon-like shelters under bark scales.

By late April or early May, around 100-200 growing degree days (GDD base 50), they begin to emerge from their cocoons and start to feed on shoots (on younger trees) and at the base of branches on older trees.

The first sign of an infestation is the appearance of small masses of pitch, white, or cream in color, which are produced as a result of larvae boring under the tree bark. As the larvae continue to tunnel and feed, more pitch will bleed from the tree.

The appearance of pitch, mixed with the sawdust-like shavings, is an indication of larval presence. These pitch masses will be soft and shiny when the larvae are active, then harden and fade to yellow or white as the infestations age.

Pitch masses are most commonly found near the trunk whorls (where branches join the main stem), but can also be seen on large branches and terminal shoots.

The 3/4-inch long mature larvae are pink to greenish in color and covered with small black spots. They are generally not seen since they are under the bark or in the pitch masses.

The feeding continues for two to three months, usually through late July. At that time, the larvae will pupate in enlarged tunnels that they have mined under the tree bark, or in pitch masses in branch whorls.

Adult moths emerge about two weeks later (around 1700 GDD base 50). The adult Zimmerman pine moth is gray, with front wings mottled with zigzag lines of red, but being nocturnal they are not often seen.

Mating takes place about a week after the adults have emerged from their pupal cases.

Eggs are deposited in mid-to-late summer on tree stems, under bark scales, or in bark crevices, and begin to hatch in a week or so.

Management

Cultural Management

Proper mulching, watering, and pruning keeps trees healthy and less susceptible to attack. 

Whenever possible, infested sections can be removed in mid-summer, before adults have a chance to emerge and lay eggs.

Chemical Management

The young larvae are most vulnerable to chemical control as they first emerge from their overwintering cocoons in spring. A new generation of larvae are also exposed for a short period of time before they begin to bore under the bark in late August, after which time chemical control measures are difficult to administer.

When damage is heavy and occurs repeatedly, insecticides are the most practical means of control.

Good coverage is vital but hard to accomplish. The spray must be applied so that the stems and main branches are thoroughly covered.

The pesticide information presented in this publication is current with federal and state regulations. The user is responsible for determining that the intended use is consistent with the label of the product being used. The information given here is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement made by The Morton Arboretum.

For more information, contact The Morton Arboretum Plant Clinic at 630-719-2424 or plantclinic@mortonarb.org.