The new technique, basal bark (tree trunk) application, could replace traditional applications made via foliage, injection or root drench, in part, by applications made to tree trunks using a backpack or conventional sprayer swathing a circular 5- to 6-foot area at an average man’s height around the trees.

Basal bark applications were not considered possible until several historical trees in California contracted Phytophthora ramorum or sudden oak death in 2003. The trees were too large to successfully foliar treat on an annual basis, and the owners did not want to injure the trees further with drilling and injection.

The trees faced probable death, until a researcher considered the bark-penetrating properties of a surfactant, Pentra-Bark, developed by Quest Products Corp. in cooperation with Agrichem of Australia, and its fungicide, Agri-Fos, a systemic fungicide that provides effective control of sudden oak death.

Pentra-Bark was specifically developed to carry pesticides through woody plant bark periderm. The question arose whether Pentra-Bark could carry other chemicals through the trunk of a tree. Trials began and it became quickly apparent that Pentra-Bark is an excellent carrier of certain systemic pesticides through basal bark.

Under a Special Local Needs Label, the historical trees were treated with Pentra-Bark and Agri-Fos via basal bark application. The trees have recovered and continue to thrive with annual basal bark applications of the materials. Pentra-Bark and Agri-Fos received full federal registration in 2003 to inhibit sudden oak death on uninfected and newly infected oaks and tanoaks. An estimated 25,000 to 30,000 trees in California, alone, have since been treated.

Agri-Fos is now fully labeled for use in basal bark applications. Additional pesticides have been tested with Pentra-Bark and their manufacturers are seeking label amendments to include basal bark applications. These include acephate, propaconazole and imidacloprid. Additional systemic pesticides are undergoing university trials.