Submitted to: Plant Disease Management Reports
Publication Type: Research Technical Update
Publication Acceptance Date: 12/12/2010
Publication Date: 3/28/2011
Citation: Krause, C.R., Horst, L. 2011. Evaluation of phytotoxicity of Ridomil Gold Copper on turnip greens, 2010. Plant Disease Management Reports. 5:V018.
Interpretive Summary: Occasionally, when pesticides are applied to crops to control plant diseases, phytotoxicity or chemical burn issues arise. Turnips were grown on muck soil at the Ohio Agricultural Research and Development Center’s Muck Crops Agricultural Research Station in Celeryville, OH. Plants were statistically analyzed for pesticide injury following treatments of Ridomil Copper Gold for control of downy mildew disease. Spots on upper surfaces appeared due to Ridomil Gold Copper applications spots appeared and then disappeared by six days after application. No chemical burn was found on control plants. Marketability of the plants produced after treatment with Ridomil Gold Copper was not affected. Therefore, the chemical is safe to use.
Technical Abstract: The experiment was conducted at the Ohio Agricultural Research and Development Center’s Muck Crops Agricultural Research Station in Celeryville, OH on Linwood muck soil, pH 6.3. No fertilizer or irrigation was used in this trial. On 6 Jul, plots were disked, leveled, and raised beds. Seeds were sown directly into the beds using a Stan Hay Vacuum seeder on 8 Jul. Plots were arranged in a randomized complete block design with four replications per treatment. Each plot consisted of two beds each 15 ft long containing three rows with 18-in. row spacing. Plots were a minimum of 15 ft apart. Treatments were applied to control Downy Mildew; Peronospora parasitica, using a tractor with a 3.0 hitch and motor driven sprayer (30psi, 32.7gal/A, 3.8mph) on a 6-8 day schedule beginning on 20 Jul and ending on 10 Aug for a total of four applications. The insecticide Sevin XLR was applied to the entire test field on 22 Jul and 2, 9 and 13 Aug to control flea beetles. The entire trial was hand weeded and hoed on 23 and 27 Jul and 4, and 10 Aug. The severity of phytotoxicity was evaluated on 22, 27, and 29 Jul and 4, 10 and 16 Aug by rating the percent of foliage affected on 10 plants from the middle of each replication 24-48 hours after each application and before sequential applications (rated on the percentage of total plant affected, see table footnote). After two applications and at harvest, average height for 10 plants from the middle of each replication was recorded. Average weight was obtained from 10 plants from the middle of each replication at harvest. Average minimum and maximum temperatures were 69.2 and 84.0oF for Jul and 69.1 and 79.0 oF for Aug; rainfall amounts were 3.3 and 2.7 in., respectively. Data were analyzed by ANOVA using SAS statistical software. Means were separated using Fisher’s Least Significant Difference test. While downy mildew pressure was high from surrounding fields, it was never observed on the turnips in this study. Within 24 hours of Ridomil Gold Copper applications, spots appeared on the top side but not the under side of leaves. These spots varied in size (within the range of spray droplet diameters) and color (from pale green to light brown). The spots decreased in size and totally disappeared by six days after application. No phytotoxicity was found on the control. The high treatment with Ridomil Gold Copper WP had significant phytotoxicity when compared to the control and other treatments. While treatments did not have any affect on the height or marketability of the plants, Ridomil Gold Copper produced plants that weighed significantly more than plants treated with Kocide 3000.