Evaluation of foliar fungicides for control of Sclerotinia stem rot of zinnia, 2014

摘要

Healthy seedlings of Zinnia 'Zahara White Improved' were transplanted into 4-in. pots containing pre-sterilized Metro-Mix 360 growing medium (Sun Gro Horticulture, Bellevue, WA) on 6 Aug. Plants were maintained in a greenhouse at a temperature of 77°F (day) and 73°F (night), watered as needed, and fertilized weekly with 150 ppm of Peters 20-10-20 water-soluble fertilizer (The Scotts Company, Marysville, OH). Fungicide treatments were applied once as a directed spray onto flowering plants on 11 Sep.Fungicides were applied "to cover" with a hand-held CO2-powered sprayer using 6503E nozzles at a pressure of 40 psi. Six single-plant replicates per treatment were arranged on a greenhouse bench in a completely randomized design. One day after fungicides were applied, on 12 Sep, plants were inoculated by uniformly spraying foliage and flowers with ascospores of Sclerotinia sclerotiorum (1x105 spores/ml) using a non-compressed hand sprayer. Ascospores were collected from carpogenic germination of sclerotia produced according to Cobb and Dillard with some modifications (The Plant Health Instructor. DOI: 10.1094/PHI-T-2004-0604-01). Non-inoculated control plants were sprayed with sterile distilled water. Plants were kept on a mist bench for 6 days post-inoculation. On the seventh day, they were transferred to a regular greenhouse bench where a humidifier maintained relative humidity near 90% throughout the duration of the trial. Disease severity was assessed weekly from 19 Sep to 10 Oct and was expressed as percentage of plant area infected. The effect of fungicide applications on disease severity over time was analyzed by one-way ANOVA.