Untreated recycled irrigation water has been shown to introduce and spread plant pathogens such as Pythium and Phytophthora in commercial nurseries. Nevertheless, few nurseries currently treat their recycled irrigation water. Instead, nurseries use prophylactic pesticides to control the spread of plant pathogens, which increases costs and promotes the growth of resistant pathogens. Of interest to California is the spread of Phytopthora ramorum, causal agent of Sudden Oak Death (SOD), responsible for the death of tens of thousands of trees in California and Oregon. This study investigated the use of a novel UV disinfection system to inactivate P. ramorum and other microbial contaminants at the National Ornamental Research Site at the Dominican University of California (NORS-DUC). In this system, the UV lamps do not come in contact with the water and hence remain free of the ‘lamp fouling’ problem. Tests on waters having the same characteristics as run-off from commercial nurseries showed a minimum of 3.7 log removal of bacterial species, 91.7% reduction of fungal counts, and 100% inactivation of the P. ramorum in the effluent. Treating the run-off from plant nurseries limits the spread of plant pathogens and enables the onsite re-use of the run-off.