Look-alikes

The first step to managing ISHB is identifying the insect. Unfortunately, many other pests and diseases cause similar symptoms on the same host trees. For example, dark staining is frequently reported on Tipu tree (Tipuana tipu), but it is rarely positive for ISHB because an entry-hole is often absent.

Do these scenarios apply to the symptoms you see? If so, consider these look-alike pests, diseases, and conditions:

 

Staining, exudate, or frass without entry-hole

Entry-hole smaller than ball-point pen tip

Some trees are host to many common PSHB lookalikes. If examining one of these species, consider its other pests and diseases:

Stonefruit (Prunus spp.)

Sycamore species

Pest Profiles


Western oak bark beetle may vector the Foamy bark canker disease. Source: Jack Kelly Clark, UC IPM
Western oak bark beetle may vector the Foamy bark canker disease. Source: Jack Kelly Clark, UC IPM

Western oak bark beetle and Foamy bark canker

Pseudopityophthorus pubipennis and Geosmithia species #41 (fungus)

Host trees: Coast live oak

Beetle size: 1.7-2.3 mm long

Entry-hole: Smaller than PSHB

Symptoms: Beetle produces light-colored frass and light staining; symptoms of disease include wet discoloration of bark, reddish sap and/or foamy liquid oozing from entry-hole, and dead wood around the entry-hole beneath the bark

Note: The beetle is native to California and typically attacks stressed or dying oaks; some of the beetles vector the Foamy bark canker disease, which was discovered relatively recently. See the UC ANR pest alert for more information.


Native to Europe, Fruittree bark beetle has become common throughout most of the United States. Source: Jack Kelly Clark, UC IPM
Native to Europe, Fruittree bark beetle has become common throughout most of the United States. Source: Jack Kelly Clark, UC IPM

Fruit tree bark beetle

Scolytus rugulosus

Host trees: Many deciduous fruit and nut trees, including stone fruits, apples, almonds

Beetle size: Beetle: 2-2.5 mm long

Entry-hole: Larger than PSHB

Symptoms: Copious gumming, oozing sap, or frass from entry-hole; tend to bore galleries close to bark surface


Monarthrum scutellare typically attacks stressed trees. Source: Jack Kelly Clark, UC IPM
Monarthrum scutellare typically attacks stressed trees. Source: Jack Kelly Clark, UC IPM

Monarthrum oak ambrosia beetles

Monarthrum dentiger, Monarthrum scutellare

Host trees: Oak species, tanoak, California buckeye; usually attacks trees that are already stressed by other pests or conditions

Beetle size: 3.5-4.1 mm (M. scutellare) or 1.9-2.44 mm (M. dentiger) long

Entry-hole: Larger than PSHB

Symptoms: Bleeding, frothing, white boring dust from entry-hole


Xyleborus saxeseni mainly attacks stressed or dying trees. Source: Cristoph Benisch, www.kerbtier.de
Xyleborus saxeseni mainly attacks stressed or dying trees. Source: Cristoph Benisch, www.kerbtier.de

Lesser shothole borer

Xyleborinus saxeseni

Host trees: Stressed or dying trees

Beetle size: 1.7-2.3 mm long

Entry-hole: Smaller than PSHB

Symptoms: Reddish frass and/or sap; wet staining and/or dead tissue around entry-hole


Rough bark and reddish frass produced by western sycamore borer. Source: John Kabashima, UCCE
Rough bark and reddish frass produced by western sycamore borer. Source: John Kabashima, UCCE

Western sycamore borer

Synanthedon resplendens

Host trees: Sycamore species (Platanus spp.), oak species (Quercus spp.), Ceanothus

Larva size: 25-38 mm long

Entry-hole: Larger than PSHB, irregular shape

Symptoms: Roughened bark, reddish frass and/or larvae pupal cases caught in bark crevices

Note: Most trees can tolerate extensive boring by this common native insect, and management is usually unnecessary


Characteristic D-shaped entry-holes of Gold-spotted oak borer. Source: Tom Coleman, USFS
Characteristic D-shaped entry-holes of Gold-spotted oak borer. Source: Tom Coleman, USFS

Gold-spotted oak borer

Agrilus auroguttatus

Host trees: Coast live oak, Canyon live oak, California black oak

Beetle size: ~10 mm long

Entry-hole: less than 4 mm wide, characteristic D-shape

Symptoms: Red or black staining running down bark, blistering and oozing on bark surface, crown thinning, twig and branch die-back

Resources: gsob.org


Discolored cavity beneath the bark of a tree infected with Xanthomonas campestris. Source: Akif Eskalen, UCANR
Discolored cavity beneath the bark of a tree infected with Xanthomonas campestris. Source: Akif Eskalen, UCANR

Xanthomonas campestris (pathogenic bacteria)

Host trees: Many, including avocado

Entry-hole: No entry-hole, but a long, deep cavity is often present

Symptoms: Exudate and bleeding (reddish on avocado) from cavity in the bark


Physical injury

Many trees respond to PSHB attacks the same way that they react to other kinds of damage: by producing staining, gumming, or exudate. Be aware of any recent management activity on the suspected tree, and look for entry-holes of the typical PSHB size and shape to avoid a misidentification of tree symptoms.

Sources of injury: pruning cuts, injection sites, staples (often used to hang strings of lights around trunk/branches), nails, other mechanical damage