PSHB Problem Case Study

The trees in our community are some of our most valuable assets; therefore, their care should only be entrusted to skilled professionals. Our Specialised Arborists and Plant Health Care Technicians are trained to diagnose, remediate, and treat detrimental conditions that lie beneath the surface.

Integrated Pest Management

Insects and diseases can result in either the decline or death of the plant if left untreated. We at Arbor Care Tree Specialists, take an Integrated Pest Management (IPM) approach to protect trees and shrubs on our clients’ properties. IPM is designed to make certain we achieve our goal of suppressing pest problems while minimising negative environmental impacts. Our Insect and Disease Management Program employs a suite of cultural practices including inspections and well-timed applications with the goal of maintaining plant health while at the same time minimising environmental impacts.

Training and Experience

Our Specialised Arborists and Plant Health Care Technicians are trained and educated on a regular basis.
We have been monitoring the PSHB for the last 9 years and are in constant communication with researchers, Arborists and Plant Health-care technicians alike in and around Southern California and other countries that has been affected by the PSHB.

What is the PSHB problem?

Adult female beetles bore into trees to construct galleries in the sapwood of the host where they grow the symbiotic fungi, including Fusarium euwallaceae, and Paracremonium pembeum. The two species of fungi are the sole nutritional source for the adults and the larvae. Unfortunately, for host plants, the Fusarium fungus is moderately pathogenic and disrupts water and nutrient movement within the vascular system causing the disease Fusarium Dieback (FD). High levels of beetle infestation and fungal infection of susceptible host trees have resulted in high levels of mortality. Symptoms of beetle attack and FD vary by host species.

The construction of tunnels by the beetles into the host severs host vascular transport resulting in variety of symptoms depending on the host including wet staining, white powdery exudate, gumming and/or frass on the outer bark surface. While there is no visible injury to the bark at this stage of colonisation, examination of the cortex and wood under the infested spot bored by the beetle reveals brown discoloured necrosis caused by the fungus.
The currently recognised host range for the beetle-fungus complex includes more than 300 tree species that can be attacked by the beetle, of which more than 100 species that can support growth of the fungus. However, currently only 63 species are used as reproductive hosts: that support beetle reproduction and support fungal growth that causes Fusarium dieback.

How can we solve/control the PHSB problem?

Due to the PSHB/Fusarium complex’s large host range, dieback and tree mortality is occurring in many landscapes – residential neighborhood, parks, urban greenways, riparian areas, natural forests and agricultural areas. Management tools are needed by homeowners, park managers, and arborists to reduce the economic and ecological impacts of this complex. Currently, management of the PSHB/ Fusarium complex is largely focused on cultural practices such as the removal of dead and heavily-infested trees and sanitation using solarization or chipping, and to a lesser extent, direct control using contact insecticides. Protection of individual trees from bark and ambrosia beetle attack has historically involved applications of liquid formulations of contact insecticides to the tree bole

Tree bark injection

Several attempts had been made to evaluate systemic insecticides as safer alternatives to insecticide bole sprays. Different active ingredients and formulations were tested and found ineffective in preventing the successful colonisation of host by adult bark beetles.

However, more recently, a phloem-mobile active ingredient was found capable of protecting loblolly pine from colonisation by Ips engravers beetles, protected ponderosa pine from mortality attributed to western pine beetle for three field seasons in California and protected green ash from emerald ash borer for 2-4 years as well.

This and other research led to registration of a benzoate for tree protection and was demonstrated effective for two years in protecting lodgepole pine against mountain pine beetle and Engelmann spruce against spruce beetle. More recently, it was found that bark injection treatments containing certain ingredients were effective in reducing PSHB attacks on California sycamore. Longer term trials determined that treatment efficacy increased significantly.

As ambrosia beetles are reliant on their symbiotic fungi for survival, targeting the beetle’s food source is also a potential means for reducing the success of the beetle/disease complex within the host. Researchers evaluated several systemic fungicides in laboratory bioassays. One of the more effective active ingredients for inhibiting Fusarium sp. growth was applied via trunk injection, and has shown efficacy against several beetle-vectored fungal diseases including oak wilt, Dutch elm disease, and laurel wilt disease.

Currently, there are no known sustainable insecticide treatments that would keep PSHB from infesting trees for >90 days and no known suitable fungicide treatment that would kill the fungus in the tree and in that way inhibit the beetle reproduction.

Treatment Intervals

Should be repeated every 4 to 6 weeks for proper control
An assessment must be done BEFORE each treatment to determine efficacy

I would love to care for your trees for many years to come. Periodically inspecting your trees will insure a long life for your trees.