2018 ASHS Annual Conference

Nursery uses a significant amount of water, fertilizers, and pesticides. In the year 2013, nurseries in the U.S. used around 775 million cubic meters of water. The number of the nurseries in the U.S. is increasing which has led to the production of the significant amount of runoff water. Isoxaben, chlorpyrifos, and oxyfluorfen are common pesticides found on nursery run-off water, which if present at a higher level may have adverse effects on nursery plants. Nursery growers are often hesitant to use of runoff water due to concerns about adverse impacts of residual pesticides. Hence our research focused on determining the damage threshold of those pesticides to common container-grown nursery plants. Hydrangea, Cornus, and Hosta are popular nursery plants and vary in the degree of sensitivity to common pesticides. Hence Hydrangea paniculata ‘Limelight', Cornus obliqua ‘Powell Gardens’, and Hosta ‘Gold Standard' were used for the study. Levels of pesticide were chosen based on their reported level in runoff water. Application rates for each pesticide were 0, 0.15, 0.35, 0.7 and 1.4 mg L^-1 of isoxaben, 0, 0.05, 0.1, 0.2 and 0.4 mg L^-1 of chlorpyrifos and 0, 0.005, 0.01, 0.015 and 0.02 mg L^-1 of oxyfluorfen. The experiment was conducted in the plastic greenhouse where the temperature was regulated at 20-25°C and 16 hours of photo-period was maintained. The different doses of pesticide were mixed with irrigation water and applied as overhead irrigation. After 3 months of pesticide application plants were compared for their growth by measuring growth index and biomass, and physical damage by visual scoring. Physiological differences were also compared by measuring gas exchange, light and dark-adapted chlorophyll fluorescence and chlorophyll content of leaves. The result shows, the damages to the plants were pesticide and species-specific. Oxyfluorfen had the greatest damage and the hydrangea was the most susceptible species. Chlorpyrifos and isoxaben never had any growth differences or visual deformities.