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

Identifying Symptoms and Damage

PSHB is a tiny beetle that spends most of its time inside a host tree, which can make it difficult to identify. If the beetle itself isn't visible, look for round entry-holes and other symptoms that are unique to each host tree. Note that there are several other beetles and pathogens that cause similar symptoms on host trees—proper identification of PSHB vs. these lookalike pests will help determine the most appropriate management solution.

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.

 

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