Observations indicate that poison oak vines that climb into oak canopies may sometimes serve as an important source of P. ramorum spores ( 1.2.2.2. Other sources of inoculum). Climbing poison oak vines should be killed when other SOD management treatments such as bay removal or chemical applications are being used to protect trees. Vines in the canopy can be killed by cutting the poison oak stems near the soil line. The cut stem may immediately be treated with an herbicide to prevent regrowth. Once the stem is severed, vines in the canopy die quickly and can be left in place.
No California native plants species other than California bay, tanoak and possibly poison oak are clearly associated with SOD risk in susceptible oaks. However, it is possible some other native foliar host species could be significant sources of P. ramorum spres in some situations. If further research shows that other native hosts can serve as sources of P. ramorum inoculum, localized removal, as discussed for California bay above, should help reduce SOD risk.
In the UK, other species have been shown to be associated with infection of canker hosts in the field. Infected rhododendrons, particularly R. ponticum, and Japanese larch produce enough P. ramorum spores to initiate trunk infections. Based on this information, SOD risk may be minimized by keeping horticultural plants that can support moderate to high levels of sporulation P. ramorum (table 1-3) at least 5-10 m from susceptible oaks. As a general rule, the area within 2.5 to 5 m of an oak trunk should be kept free of introduced plant materials of any kind and should not receive irrigation to minimize the risk of other oak diseases.