|May Iii, W|
|Wechter, William - Pat|
Submitted to: Plant Disease Management Reports
Publication Type: Research Notes
Publication Acceptance Date: 1/10/2007
Publication Date: 3/1/2007
Citation: Keinath, A.P., Dubose, V.B., May Iii, W.H., Wechter, W.P. 2007. Evaluation of Biopesticides to Manage Bacterial Leaf Spots on Turnip Greens, 2006. Plant Disease Management Reports (Online). Report 1:V104. DOI: 10.1094/PDMR01. The American Phytopathological Society, St Paul, MN.
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. Fertilizing, watering with overhead center-pivot irrigation, and insect control were done by the cooperating grower. The experimental design was a randomized complete block with six replications. Leaf spot severity was rated with a 0-to-15 point Horsfall-Barratt scale. When turnip leaves reached mature, marketable size, the nonsprayed, Actigard alone, and Kocide alone treatments were harvested by arbitrarily selecting a 20-in.-long section in each of two rows of each plot and cutting all foliage in the two sections. Fresh weight was measured and then 100 leaves were selected arbitrarily and sorted into healthy and diseased classes. Area under the disease progress curve (AUDPC) and yield data were analyzed with SAS, PROC MIXED, version 8e. Disease symptoms were not present at the first rating. P. syringae pv. maculicola was isolated from all leaves collected from nonsprayed plots at the first two ratings and at harvest. A leaf-spotting pathovar of X. campestris was isolated from a few plants at the second rating and from most plants at harvest. (Pathovar identification of this xanthomonad is in progress.) Five treatments reduced AUDPC compared with the nonsprayed control. The biopesticides Proud 3 (5.6% thyme oil), Actinovate (Streptomyces lydicus), and Physpe (a plant activator), the antibiotic Kasumin (kasugamycin), and the phosphorus acid ProPhyt applied alone did not reduce AUDPC compared with the nonsprayed control. Moreover, when these five products were combined with Actigard, ProPhyt, or Kocide, the combination treatments did not differ significantly from Actigard, ProPhyt, or Kocide applied alone. Thus, the reduction in disease observed with Physpe plus Kocide, ProPhyt plus Actigard, and Proud 3 plus Actigard was due to Kocide and Actigard. It was not apparent why Actinovate plus Actigard did not reduce AUDPC. Actigard applied alone increased fresh weight of turnip greens compared with Kocide and the nonsprayed control (a 64% increase). Actigard and Kocide increased the percentage of healthy leaves by over 100% compared with the nonsprayed control. However, the level of disease was still too great to be acceptable to growers.