PSHB: The Beetle Invading Southern California Trees

The beetle known as the polyphagous shothole borer (PSHB) was first identified in Southern California in 2003 and began being notable in 2010 when it was presumed to be the cause of tree decline in Long Beach, California on Box elder trees (Acer negundo).

More recently, we are seeing them invade a variety of other species and killing them at an alarming rate.

The PSHB bores into the tree and then infects it with a fungal pathogen which eventually kills the tree in as short as 3 months.

Below a summary of the PSHB:

PROFILE

Insect Type: Boring Beetle

Origin: Traced from Southeast Asia

First Identified: In Southern California in 2003

WHAT WE KNOW

- - Carries fungal pathogen on their mouth
  - Pathogen enters host tree with beetle
  - Males cannot fly and remain in tree for reproduction
  - Females exit tree to locate nearby suitable host, maximum reproductive flight is February through April
  - Beetle entry and exit holes can be found on tree and near the symptoms
  - Feeds on resources within tree until those resources are exhausted or when population within tree becomes to competitive
  - No native predator/parasite for control/suppression

SYMPTOMS

Initial response: die back of small twigs

Secondary: larger branches may die and/or become unstable. Entire bench failures have been reported

POSSIBLE OUTCOME

1) No infection—reason for repellency is not clear

2) Beetle attacks tree but does not reproduce:

1. 1. May lead to water stress and potential decline, secondary insect/pathogen attack, twig dieback.

3) Beetle attacks, inoculates with fungi successfully and reproduces with beetle/fungi complex

1. 1. Response vary from outright death, large branch decline/death, minor twig die-
    back.
  2. Deterioration of wood from (possibly) second decay organism may destabilize
    wood leading to whole branch/tree failure.

WHAT IS A Reproductive Host Tree?

A tree where fungi successfully develop within that host tree. When this fungi is suitable for growing, the female beetle remains in the tree and reproduces (up to 6 generations = up to 64M insects).

TRADITIONAL Treatment Method

OPTION A: Onyx + Merit

OPTION B: Safari + Merit

A PLUS Platinum Treatment Method

Bacillus Subtilis – Applied Monthly
Imidacloprid 75 WSP Soil Drench ***
Bifenthrin Branch, Canopy and Trunk Treatments no lower than 4.5 Feet on trunk
Safari 20 SG – Dinotefuran Trunk Spray up to 4 feet of trunk
Aliette Soil Drench – Phytophthora prevention
Soil Improvement Treatments to promote chemical uptake
Tree Inventory and Database Tracking of treatments and tree health through ArborPlus

LIMITATIONS

No treatment regime or combination has provided substantial control over time
Soil moisture and condition is necessary for uptake of the treatment within the tree. Particularly for conifer trees.
Industry based research indicated 85% control, however field observations have been unable to verify this efficacy.

PRECAUTIONS

When pruning trees, use hand saws when possible and sterilize the tools to prevent the spread of the pathogen. Ideally, between each cut.
Chain saws cannot be sterilized effectively.
When removing entire tree, grind stump and surface anchor roots.
Do no move/transport large intact parts of the tree off the site.
Chip all infested materials to a 1.0” or smaller grind – 99% of beetles are killed when debris is chipped to this size
If must be taken off-site, must be covered to ensure beetles are contained.