|Wechter, William - Pat|
Submitted to: Fungicide and Nematocide Tests
Publication Type: Research Notes
Publication Acceptance Date: 2/1/2006
Publication Date: 4/1/2006
Citation: Keinath, A.P., Dubose, V.B., May, W.H., Wechter, W.P. 2006. Effect of Actigard on Xanthomonas leaf spot on rape greens, 2005. Fungicide and Nematocide Tests. 61:V058. Interpretive Summary: Interpretive summary not required.
Technical Abstract: The trial was conducted on a large commercial farm in Pelion, SC, with a history of bacterial leaf spot diseases on leafy brassica greens. The soil was Lakeland sand. The field was seeded on 4 Aug with five rows per bed, which were spaced 6 ft on center. Fertility, watering with overhead center-pivot irrigation, and pest control were done by the cooperating grower. The experimental design was a randomized complete block with eight replications. Actigard was applied to the plots with a CO2-backpack sprayer at 45 gpa, 60 psi. The first application was made on 8 Aug when only the cotyledons of plants had emerged. Because over 3 in. of rain fell later that day, four additional applications were made at weekly intervals. Leaf spot severity was rated with a 0-to-15 point Horsfall-Barratt scale on 29 Aug and 5 and 12 Sep. Data were analyzed with SAS, PROC MIXED, version 8.0. The respective avg max/min temperature and rainfall for Aug and Sep were: 90.5/73.0oF and 3.36 in. and 87.6/70.7 oF and 0.97 in. Disease severity was low because of dry weather during this trial. Both rates of Actigard significantly reduced Xanthomonas leaf spot compared to the nonsprayed control; the average reduction in leaf spot severity was 55%. No phytotoxicity or stunting of plants was observed in any sprayed plots. The presence of the causal agent of Xanthomonas leaf spot, Xanthomonas campestris, was confirmed by pathogen isolation from nonsprayed leaves and leaves sprayed with the labeled rate of Actigard. Four applications of this product, the maximum number permitted according to the label, may not be economical on leafy brassica greens without a higher degree of control, considering each application of Actigard at 1.0 oz/A costs approximately $55.