Effects of formulation and surfactant on control of early leaf spot of peanut with tebuconazole

Authors: DAMICONE, J - OKLAHOMA STATE UNIV; Melouk, Hassan

Submitted to: American Peanut Research and Education Society Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 6/13/2006
Publication Date: 7/11/2006
Citation: Damicone, J.P., Melouk, H.A. 2006. Effects of formulation and surfactant on control of early leaf spot of peanut with tebuconazole [abstract]. In: 2006 Proceedings of the American Peanut Research and Education Society, July 11-14, 2006, Savannah, Georgia. p. 50. Available: http://www.apres.okstate.edu/Vol%2038%20Proc.pdf.

Interpretive Summary:

Technical Abstract: Prior to 1997, control of early leaf spot with the DMI fungicide tebuconazole, applied in a block of 4 mid-season applications scheduled between 2 applications of chlorothalonil, was similar to a full-season program with chlorothalonil. Periodically since 1997, control of early leaf spot with tebuconazole has not been equivalent to chlorothalonil. Modifications in the commercial formulations during this time period may have contributed to the reduced disease control with tebuconazole. In 2005, tebuconazole (0.20 lb/A) was applied in the block program described above using 2004 and 2005 commercial formulations, and using an old (early 1990s) experimental formulation Bay HWG 1608. The 2004 formulation and Bay HWG 1608 observed were applied with and without 0.125% surfactant. Tebuconazole treatments were compared to a full-season chlorothalonil (1.12 lb/A), and a block program with another DMI fungicide prothioconazole (0.18 lb/A). Pressure from early leaf spot on cv. Tamspan 90 was severe as untreated control plots were 95% defoliated and yielded only 2,134 lb/A. All of the fungicide programs reduced defoliation and increased yields compared to the untreated control. The lowest level of defoliation (23% defoliation) was achieved with prothioconazole. Defoliation levels were similar among full-season chlorothalonil (65%) and the tebuconazole formulations (72-75%). However, the addition of surfactant resulted in reduced defoliation for the 2004 formulation (52%) and Bay HWG 1608 (53%) compared to the respective formulations without surfactant. Yields were similar for all fungicide programs and ranged from 2956 to 3477 lb/A. In greenhouse plants inoculated with 4X104 conidia/ml of an isolate of Cercospora arachidicola never exposed to DMI fungicides, disease control with tebuconazole did not differ among the 2004 formulation of Bay HWG 1608, either with or without surfactant. In the greenhouse trial, disease control with tebuconazole was similar to chlorothalonil when the fungicides were applied up to 2 days after inoculation, but was better than chlorothalonil when applied at 3 and 4 days after inoculation. The addition of surfactant was more important than formulation in the control of early leaf spot with tebuconazole. Infectivity studies are needed with isolates of C. arachidicola from fields with along history of DMI usage.