Oak Wilt Eradication in Gro-Bark Composting

Pathogen Background

Oak wilt is a systemic fungal infection caused by Bretziella fagacearum targeting the vascular system of oak trees and restricting water and nutrient flow resulting in oak tree deaths. Oak wilt spreads above ground through vector transmission by sap beetles and human transportation of infected wood products as well as belowground through direct contact of roots between trees.

Symptoms vary between red and white oak trees as red oak trees are more susceptible and experience faster wilt. One prominent common symptom includes browning foliage beginning at the tip of the leaf and traveling to the base. Premature leaf fall, including green leaves, is another common symptom. Bulges in the bark, which are indicative of sporulating areas, may also be observed as well as distinct vascular streaking in an infected tree’s xylem. It can take several years before symptoms appear on a white oak, but they are still carriers of this vascular disease and can continue to spread infection before death.

Infected trees should be removed and disposed of by a trained professional to minimize cross contamination. Surrounding trees may have to be removed to disrupt the root system and prevent further belowground spread of the pathogen

‍Pathogen Eradication in Composting

Composting is the aerobic process of decomposing organic material to produce a nutrient-rich soil amendment. Throughout this process, heat is generated and temperatures of the organic material reach 54-71°C.

Gro-Bark complies with the provincial Ontario Compost Quality Standards (OCQA), Reg 101/94, using outdoor windrows. This regulation states that windrows must maintain a minimum temperature of 55°C for 15 days during the active phase to ensure inactivation of pathogens that thrive in temperatures between 5-35°C. Specifically, B. fagacerum cannot withstand temperatures above 32°C and can be inactivate when exposed to ≥54°C for at least 24 hours OR ≥43°C for at least 48 hours. Therefore, Gro-Bark’s composting method in which windrows reach ≥55°C for 15 days is an effective method of inactivating oak wilt infected trees.