The City’s tree maintenance company West Coast Arborist will begin on August 15, 2016, removing trees that are infested with the Polyphagous Shot Hole Borer (PSHB). This infestation causes the trees to die. The most common issue and concern is broken branches from the dying trees as they fall and create hazards. Approximately 100 trees at Crown Valley Park and eight (8) trees at the Sea Country Senior and Community Center will be removed.
Drought conditions have worsened this problem and the beetle has already killed thousands of trees in California. As these conditions persist, it is expected that more trees in City parks, median islands, and slopes will succumb to this disease. City staff and contractors will continually examine City-owned trees to assess their viability. Unfortunately, there are no preventive measures that can be taken at this time. By proactively removing the infected trees, the risk of harm from falling trees and limbs, as well as the spread of the disease, will be reduced.
Residents are encouraged to check their trees for signs of infestation and distress. To learn more Click Here.
As trees are removed to combat the disease, the City will begin planting new trees when it is cooler and potential rainfall will help them to get established. The replacement trees will be compatible with the surrounding area and resistant to attacks by the beetles.
Questions can be directed to the City of Laguna Niguel Public Works Department at (949) 362-4377.
Additional Information on PSHB
Beetle and Fungal Complex: The Polyphagous Shot Hole Borer (PSHB), Euwallacea sp., is an invasive beetle that vectors a disease called Fusarium Dieback (FD). The disease stops the flow of water and nutrients in over 137 susceptible tree species, which can lead to the death of individual branches or, in severe cases, the entire tree. It is caused by the fungi that the beetle uses as a food source: Fusarium euwallaceae, Graphium euwallaceae, and Paracremonium pembeum. PSHB attacks a wide variety of host species. The beetles bore tunnels (galleries) in which to lay their eggs and grow the fungi. A closely related Euwallacea species, the Kuroshio Shot Hole Borer (KSHB), has been detected throughout Orange and San Diego Counties. It is physically identical to PSHB and also spreads a fungal disease caused by other species of Fusarium and Graphium.
Description of the pest: Polyphagous shot hole borer (PSHB) and Kuroshio shot hole borer (KSHB) are genetically different invasive species, but morphologically they are indistinguishable. Females are black and 0.07 to1.0 inch (1.8–2.5 mm) long. Males are brown and smaller than females at 0.06 inch (1.5 mm) long. The female tunnels into a wide variety of host trees forming galleries, where it lays its eggs. More females are produced than males. Mature siblings mate with each other so that females leaving to start their own galleries are already pregnant. Males do not fly, but stay in the host tree.
Damage: A host tree’s visible response to a beetle’s attack varies among host species. Staining, sugary exudate (also called a sugar volcano), gumming, and frass may be noticeable before the tiny beetles are found. The beetle’s entry and exit holes, which are about 0.03 inch (0.85 mm) in diameter, can be located beneath or near the symptoms. The abdomen of the female beetle can sometimes be seen sticking out of the hole. Advanced fungal infections will eventually lead to branch dieback. Rapid spread of the beetle and fungi throughout various land-use areas is attributed to the diverse range and quantity of suitable hosts in southern California.
Management: Currently there are no control measures for this pest. Early detection of infestations and removal of the infested branches will help reduce beetle numbers and the extent of disease spread.