Invasive Shot Hole Borers
Invasive Shot Hole Borers
Invasive Shot Hole Borers
University of California
Invasive Shot Hole Borers

Identifying Symptoms and Damage

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

Because ISHB is just a tiny beetle which spends most of its life inside the tree, it can be difficult to find, let alone identify the beetle itself. If you’re unable to find a ISHB beetle on the bark surface, start looking for small (ball point pen tip-sized), round entry-holes on the bark. In addition to entry-holes, trees under attack can exhibit a variety of other signs of ISHB/FD infestation, like staining, gumming, presence of frass (thin sawdust), and sugary exudates (see descriptions below). Each tree species react differently to ISHB attacks, so the combination of symptoms can be unique to each host tree species (see the Field Guide to the right for guidance). Finally, there are other beetles and disease-causing pathogens that can cause signs similar signs to ISHB/FD; use this lookalike pests guide to help determine if ISHB/FD is a likely cause of the tree’s problems or another pest and/or pathogen may be to blame. Once the correct identification of the problem is made, you can use this handout and this management assessment tool to choose the most appropriate management action.

You can access the updated (04.2017) online field guide here:    Online Field Guide 

 
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Select a tree to view PSHB symptoms on that species.

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Entry-Hole

 

The typical entry-hole to a PSHB 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. It may also be plugged or covered by sap, exudate, or frass (sawdust from boring) from the tree. If sending photos to a specialist for identification, include a picture with a pen for scale.

 

Symptoms of Attack

 

Entry-holes are typically accompanied by attack symptoms, which are the host 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 species, oak species)
  • Gumming: thick resin that sometimes pushes the beetle out of the gallery (e.g. silk trees, Koelreuteria species like Goldenrain tree)
  • Sugary exudate: may form white, powdery "volcanoes" (e.g. avocado)
  • Frass: produced by the beetle's boring activity, may be present on any host tree depending on the infestation level (long "matchsticks" of frass have been observed on box elder, coral tree, and willow species)

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

 

Branch Dieback

 

Advanced infestations lead to branch dieback and overall decline. Watch for beetle attacks concentrated on a branch or in the branch collar (the point of attachment between the main trunk and a branch)—infestations in this area can lead to limb failure.

 

Signs of Infection

 

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

 

This site contains research-based information for education purposes. For specific guidance check with your local land management regulatory authorities. Any information on products and practices is for educational purposes only and does not constitute an endorsement or recommendation by the University of California.

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