Best Management Practices
On Monday May 1, 2007 representatives of Tree Solutions attended a seven-hour Sudden Oak Death/ Phytophthora ramorum Wildland training session. The session took place in the Santa Cruz Mountains, off Bear Creek road in Los Gatos, CA.
It was presented by The California Oak Mortality Task Force. Leading the training sessions were biologists, pathologists, researchers and managers from U.C. Berkeley, U.C. Davis, U.S.D.A., UC Cooperative Extension and the Department of Forestry.
The morning session focused on current regulations, treatments, diagnosis, research updates and best management practices. The afternoon session was field study. Four field-training stations were set up in various locations at an adjacent Regional Open Space Reserve.
These stations focused on:
- Field symptoms and sampling
- Agrifos and Pentrabark application
- Wildland surveys and GPS
- General Q/A session
Best Management Practices
Presented at the meeting were new best management practices (BMP) and treatment protocol. Due to high amounts of pathogen inoculum dispersal from the leaves of California Bay Laurel (Umbellularia californica) and Tan Oak (Lithocarpus densiflorus) trees, a buffer zone of 5-30 meters is recommended. The aforementioned trees carry immense amounts of the disease spores.
During winter and spring rain events, the spores are dispersed by wind and water splash onto the trunks of adjacent trees. It is believed that trees constantly bombarded by the inoculum may become infected even if they are protected with Agrifos/Pentrabark drench treatment.
The best oak tree pruning dates are from July to October. This is when the pathogen is least likely to be active. In active SOD areas, it is especially important not to prune during the months of March thru May. This is when the pathogen is most active, especially during a wet springtime rainy season. It is recommended that the pruned material be chipped and spread out on-site. Large wood should be split and dried.
Two approved treatment methods are available: Trunk drench and trunk injection. The fungicide is applied and then distributed throughout the tree roots and canopy via its vascular transport system.
Trunk drench is the easiest application method. Agrifos/Pentrabark mixture is sprayed onto the trunk of a tree. It requires more material than injection but less expertise. Care must be taken, because the product is phytotoxic. Spray drift from the mixture damages mosses, lichen and leaves of target trees and other adjacent plants. As with any chemical application, personal protection of the applicator is important.
Trunk injection requires a specialized injector that applies constant pressure so the tree can accept the material. It also requires a higher degree of expertise.
Treatment Timing and Schedule
Optimum treatment timing for trees proven to become infected by the pathogen Phytophthora ramorum; Coast live oak (Quercus agrifolia), Shreve’s oak (Quercus parvula var. shrevei) and Canyon live oak (Quercus chrysolepis),Tan oak (Lithocarpus densiflorus), are late fall and mid winter. The late fall treatment timing coincides with the first seasonal drop in temperature. This usually occurs between the last week of October and first week of November. This timing is most important when using the injection method.
The pre-winter recommendation is based on the need to treat before build-up of high inoculum levels. Although not addressed at the meeting, the deciduous California black oak (Quercus kelloggii) should be treated at least three to six weeks before fall leaf-drop and/or after flowering in spring. Fall treatment is optimum because it ensures tree protection before heavy inoculum build-up.
UC Cooperative Extension, Eureka California recommends two initial applications spaced six months apart with follow-up applications at twelve-month intervals. After the initial application and booster application is applied, it is recommended that the annual application be applied in November of the current year.If the initial application occurs in fall, the recommended treatment schedule is as follows:
- Fall 2008 initial application. Spring 2009 2nd application, Fall 2010 booster, Fall 2011 booster, Fall 2012 booster cont….
- Spring 2008 initial application, Fall 2008 2nd application, Fall 2009 booster, Fall 2010 booster cont….
Treatment is most effective when the tree’s vascular system is active.
Summary and Recommendations
- Removal of certain adjacent trees within a prescribed buffer zone along with an application of approved fungicide will give oak trees the best chance for survival.
- Chipping of pruned material and spread on-site is recommended.
- Treatment timing and expertise of the applicator is very important.
- Oak tree pruning dates are important to help prevent infection from occurring or spreading.
- Tree management by well-informed and skilled certified arborists is important.
- Drench applications may burn plant parts, moss and lichen of target and adjacent trees being treated.
- Plants need to be protected from chemical drift when sprayed. Prior to spraying, tarp adjacent plants to protect from chemical drift.
- Trunk injection requires a specialized injector that uses constant pressure. It is an option to spraying. Injection is an alternative to prevent chemical trespass. It also requires a high degree of expertise.