Arborjet Revolutionary Plant Health Solutions

Polyphagous Shot Hole Borer

Polyphagous Shot Hole Borer (PSHB) is an exotic ambrosia beetle that was first detected in 2003 in Southern California and was recently found to be killing or infesting several hundred species of trees. It is currently found in L.A., Orange, San Bernardino, western Riverside, and San Diego Counties.

The “ambrosia” name refers to a symbiotic fungus that is carried by the female in special organs in her mouth parts. The fungus is grown in the beetle galleries and both the adult beetles and larvae feed on the fungi. The adult beetles are very small, ranging from 0.05 to 0.1 inches in length. They come in a range of shades between black (females) and brown (males) coloring. While this beetle attacks a large number of plant species, the majority of which are hardwoods, it can only reproduce in 31 species including maples, sycamore, oaks, willows, alders, and avocado.

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The characteristics of PSHB attack and fungus infection differ among tree species. The beetle commonly attacks the main stem and larger branches of trees and shrubs, but injury can be found on twigs as small as 1 inch in diameter. The beetle produces a very precise, perfectly round, tiny (< 0.1 inches in diameter) entry hole in most trees. Wet staining and discoloration on the bark of the main stem and branches are early symptoms of beetle attack. Depending on the tree species attacked, PSHB injury can be identified either by staining, gumming, or a sugaring response on the outer bark. Infection with the fungus can cause leaf discoloration and wilting, dieback of entire branches, and tree mortality.

A: Female polyphagous shot hole borer
B: Polyphagous shot hole borer caused bark staining
on sycamore
C: Polyphagous shot hole borer damage
D: Polyphagous shot hole borer attack point and bark
stain on sycamore
Photo A taken by: Stacy Hishinuma, UC Davis, Department of Entomology
Photo B taken by: Don Grosman, Arborjet
Photo C taken by: Don Grosman, Arborjet
Photo D taken by: Don Grosman, Arborjet


Preventative treatment with TREE-äge® Insecticide prior to or just after initial PSHB attack is the better management strategy. If a tree is showing light to moderate attack levels, treatment with TREE-äge followed by Propizol® Fungicide is recommended at rates shown on product labels. TREE-äge provides 2 years of control of the beetle, while Propizol will protect trees from the fungi introduced by the ambrosia beetle. Use a soil surfactant, such as NutriRoot, as a sub-surface injection or drench, in combination with watering to encourage root growth, increase penetration of water into the soil, and to assure better translocation of the formulations throughout the tree.


In addition to the pests noted on the TREE-äge federally registered label, Arborjet supports a FIFRA Section 2(ee) recommendation for TREE-äge insecticide to control additional bud and leaf and shoot, stem, trunk and branch pests.  Please see the section 2(ee) recommendation to confirm that the recommendation is applicable in your state.

When to Treat

The most significant damage occurs from May through October so if PSHB is found near or on trees under your care, treatments should be made immediately.

Generally, the best seasons for injection are spring and fall, since the best uptake occurs when trees are actively transpiring, but treatments can be made at any time of the year when there is good soil moisture to encourage translocation of the systemic formulations.
The environmental conditions that favor uptake are adequate soil moisture and relatively high humidity. Soil temperature should be above 40°F for trunk injection. If treating trees in the summer, inject in the morning for the quickest uptake. Hot weather and/or dry soil conditions may slow translocation of the product into the foliage, so consider using a soil surfactant, such as NutriRoot, in combination with watering before and after treatment application.

What to Expect After Treatment

Trunk injections with insecticide or combined with fungicide will distribute upward in the tree within 4-6 weeks with adequate soil moisture. For trees in natural, non-irrigated
areas with questionable soil moisture, consider using NutriRoot to enable trees to extract water from the soil, reducing the need for watering, and resulting in faster and better movement of systemic products even in drought conditions.

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Uploaded: 10/12/2015

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