Sequoia Pitch Moth

Unsightly pitch mass caused by Sequoia Pitch Moth

Insect Profile

What is Sequoia Pitch Moth?

Sequoia Pitch Moth (SPM) is a type of clearwing moth that resembles a wasp or yellow jacket with its black and yellow stripes. Its larvae feed on trees and cause damage. It causes trees to ooze, and is sometimes mistaken for bark beetles. Although it is much less destructive than bark beetles, it can cause severe and unsightly damage to trees, and increase risk of tree failure. Eradication is very difficult, and management should be focused on suppressing populations to tolerable levels.

Sequioa Pitch Moth adult in Reno, NV ©Aspect Tree Care 2024

What types of trees are susceptible?

The most susceptible trees are Austrian and Scotch Pines [1][2], but we also see SPM on other pines, spruces, and firs. Essentially, trees of the pine family that have a low or moderate drought tolerance are susceptible. We rarely observe trees with high tolerance for drought suffering severe infestations unless there are other predisposing factors present. Giant sequoias, deodar cedars, atlas cedars, and incense-cedars are resistant based on my observations.

Consequences and Severity

SPM has increased in frequency and severity in recent years [2]. The damage is caused by larvae feeding on cambium tissue and sapwood and mostly affects the appearance of trees, but it can cause tree death in severe cases [1][2]. Numerous globby pitch masses are unsightly and drip in warm temps. Large populations of SPM can cause branch dieback and stress [2]. I have observed large branch failures and large tree tops fail due to SPM. Their feeding patterns perforate the sapwood, making branches break more easily. Stressed trees are more susceptible to other pests/disorders and can appear sickly with yellowing and thinning foliage. Repeated infestations over multiple years can magnify damage, especially on smaller diameter branches, tree tops, and young trees due to girdling [2].

Insect Life Cycle

One generation of SPM takes almost 2 years to develop from the time of egg-laying until adult emergence [2]. Adults emerge and lay eggs as early as April and as late as August every year, with a peak in June or July [2]. They prefer to lay eggs on bark near branch unions, wounds, and fresh pruning cuts [1]. Larvae hatch from eggs after about two weeks, and begin feeding on trees, creating pitch masses [2]. They continue to feed throughout the spring, summer, and fall, overwinter (not feeding) under pitch masses, and resume feeding again in early spring [2]. It will continue in this larval stage for another year or so before pupating (not feeding) for one month before it emerges as an adult [2]. Generations of SPM overlap and new larvae hatch every year [1].

Diagnostic Clues

The most obvious sign is the presence of large pitch masses. They are thick off-white globs of sap tinted red/brown from frass, which is a mixture of sawdust and excrement from the chewing larva. After removing a pitch mass, and inside a bore hole, you should find a single larva, up to 1 ¼” long, and pinkish-white with a brown head [2]. They can be found at any time of year, usually on trunks and larger branches [1]. We sometimes find them on branches 2” in diameter or smaller, which often corresponds with flagging due to girdling. Flagging is the browning of needles at the tip of a branch that contrasts with surrounding green needles. Old (inactive) pitch masses are hardened, usually coated in pollen, and sometimes contain pupal skins [1]. Pupal skins are about ¾” and dark brown [2].

Management

Cultural and Mechanical Control

Physically remove resin masses and remove or kill larvae [2]. Avoid pruning or injuring trees from February through September [2]. Plant resistant trees and keep all susceptible trees healthy by mulching, deep watering, managing soil and root health, preventing mechanical damage, and managing other pests/disorders [2]. In all but severe cases, this should be sufficient to suppress populations of SPM to tolerable levels.

Chemical Control

Systemic insecticides

In severe cases of SPM, and for large trees where it is impractical to remove all pitch masses and larvae, we recommend using insecticides containing the active ingredient emamectin benzoate. Our choice is Arborjet’s TREE-age R10, applied by trunk injection on trees larger than 4” in diameter at breast height (DBH) [3]. More research is needed, but there is some scientific evidence of its effectiveness against SPM [2], and it is commonly used to manage many other wood-boring insects like Emerald Ash Borer and bark beetles.

After treatment, expect suppression of SPM to tolerable levels for 1-2 years when combined with cultural controls for tree health. It will also safeguard trees from many other pests including bark beetles.

Systemic insecticides containing the active ingredients imidacloprid and dinotefuran are not effective [1].

Using the QUIK-jet AIR® by Arborjet to inject a tree to control Sequioa Pitch Moth

Other insecticides

No contact insecticides and biorational insecticides have been found to be effective [2].

References

1. Sequoia Pitch Moth. https://extension.usu.edu/pests/ipm/ornamental-pest-guide/arthopods/wood-borers/sequoia-pitch-moth

2. Sequoia Pitch Moth in Pines. https://digitalcommons.usu.edu/extension_curall/1626/

3. TREE-age R10 by Arborjet. https://arborjet.com/product/tree-age-r10/