Diagnosis

Do You Have ISHB on Your Property?

This online assessment tool is intended to help evaluate the presence of ISHB on your property. Consider the level of infestation, potential safety hazards, economic and ecological tree value, available resources, and factors unique to each situation when using this tool. Simply click the link below for access.

ISHB Detection & Management Assessment Tool

Identifying Signs and Symptoms of ISHB Attack and Fusarium Dieback (FD) in Trees

Because ISHB are tiny beetles that spend most of their lives inside the tree, it can be difficult to find and identify them. However, infested trees show signs and symptoms that can help us determine if the tree is infested with ISHB-FD.

Beetle Entry Hole

The most accurate way to visually determine if a tree is infested with ISHB is to find beetle entry holes that are the right size and shape. The typical entry hole to an ISHB gallery is perfectly round and about 0.85 mm (less than 0.04 inches) in diameter, or about the size of the tip of a ballpoint pen. The abdomen of the female beetle can sometimes be seen protruding from the entry hole. The entry hole may also be plugged or covered by sap, exudate, or frass (sawdust from boring) from the tree. When sending photos to a specialist for identification, include a picture with a pen for scale. ISHB galleries run perpendicular to the trunk. If ISHB are present, shaving off bark will reveal a round gallery up to 2 inches deep in the wood, surrounded by darkened, diseased wood.

Signs of Infection

Fusarium causes dark discoloration of the wood around the beetle gallery. Lightly scraping away bark from around the entry hole will reveal dark brown to black staining.

Source: BeaNobua-Behrmann, UCANR
Source: Monica Dimson, UCANR
Source: Bea Nobua-Behrmann, UCANR
Source: Akif Eskalen, UCANR

Disposal of infested material

Invasive shot hole borers can survive in downed wood for up to several months. Appropriate disposal of infested green waste is necessary to avoid spreading this pest to new areas. See guidelines for proper disposal of infested wood.

Other Symptoms of Attack

Entry holes are typically accompanied by attack symptoms, which are the tree's visible response to stress. These symptoms and examples of species that produce them  include:

  • Staining: may be wet and dark or dry and light-colored (e.g. sycamore trees, oak trees)
  • Gumming: thick resin that sometimes pushes the beetle out of the gallery (e.g. silk trees, Koelreuteria species like Goldenrain tree)
  • White powdery exudate: may form "sugary volcanoes" that appear to be crystalline foam (e.g. avocado)
  • Frass: produced by the beetle's boring activity, may be present on any host tree especially when infestation level is high. It can appear as long "matchsticks" of frass (e.g. box elder, coral tree, and willow species)

Some of these symptoms may be washed away or obscured by rain or irrigation water.

staining
gumming
white-powdery-exudate
frass

Each tree species reacts differently to ISHB attacks. The combination of symptoms can be unique to each host tree species. Use the following tool as guidance to see how the symptoms may look in many of the species of reproductive hosts.

Select a tree to view ISHB symptoms on that species.

Search by common name

Search by botanic name

 

Branch Dieback

Advanced infestations lead to branch dieback and overall decline. Watch for beetle attacks concentrated on a branch or branch collar. Infestations in this area can lead to limb failure.

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Look-alikes

The first step to a successful management program is the correct identification of the pest. Unfortunately, many other pests and diseases cause similar symptoms to ISHB-FD and can appear on the same plant species. The easiest way to distinguish ISHB-FD symptoms from the ones caused by other pests and diseases is the presence of an entry hole that is the right size and shape.

Visit the UC IPM web page for more information about pests of landscape trees.

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 ISHB 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 (0.07 -0.09 in) long

Entry-hole: Smaller than ISHB

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, Fruit tree bark beetle has become common throughout most of the United States. Source: Jack Kelly Clark, UC IPM
Native to Europe, Fruit tree 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 (0.08 – 0.1 in) long

Entry-hole: Larger than ISHB

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 (0.14 – 0.16 in) (M. scutellare) or 1.9-2.44 mm (0.07 – 0.1 in) (M. dentiger) long

Entry-hole: Larger than ISHB

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 borerXyleborinus saxeseni

Host trees: Stressed or dying trees

Beetle size: 1.7-2.3 mm (0.07 – 0.09 in) long

Entry-hole: Smaller than ISHB

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 (1 – 1.5 in) long

Entry-hole: Larger than ISHB, 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 (0.4 in) long

Entry-hole: less than 4 mm (0.16 in) 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 ISHB 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 ISHB 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