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Degree

Master of Science, Ohio State University, Plant Pathology, 2009.

Abstract

Dollar spot caused by Sclerotinia homoeocarpa is one of the most important diseases of turfgrass. Previous research has shown that fungicide applications to asymptomatic turfgrass in the fall and/or spring, at times when fungicide applications are not typically made, can reduce dollar spot severity the following growing season. The purpose of this research was to: (a) validate previous findings regarding the efficacy of late fall and/or early spring fungicide applications to suppress dollar spot, and (b) to determine the relationship between air temperature and the timing of all effective fall/spring fungicide applications with the goal of developing practical recommendations for golf course superintendents. Replicated field studies were established at two locations within central Ohio from October 2006 to July 2008 to assess the impact of late fall and early spring fungicide applications to suppress dollar spot. Mean daily air temperatures were collected through out the 2-year study. Single fall applications of the fungicides propiconazole and chlorothalonil, as a tank mix, had no impact on disease severity the following season. In contrast, multiple sequential fall applications of these same fungicides did significantly reduce dollar spot severity. Both single and sequential multiple fungicide applications in March and April resulted in significantly less dollar spot severity the following summer during both years of the study. The effective single spring applications can be classified into two general groups based on the timing of when these applications were made: “Early Spring” applications (at The Ohio Turfgrass Research and Educational Facilities (OTF) on April 3; at both locations April 10, 17, 24; and at The Golf Club (TGC) on May 5, 2007); and “Late Spring” applications (at TGC on May 15, 29, June 5; and at OTF on June 5 and 12, 2007). Two distinct groups of effective single spray applications were also observed at OTF in “Early Spring” of 2008 on March 17, 25 April 2, 15, 22, 29 and May 6; and “Late Spring” on May 27 June 9, 17, 25, and July 1, 2008. The average air temperature range associated with these “Early Spring” effective dates in 2006-07 trial year was 41-71 oF and at TGC 44-70 oF. Growing degree-day (GDD) measurements for the effective single applications at both locations and years have a very wide range from GGD33 344 – 1348; GGD40 160 – 827; and GGD50 28 –340. GDD may be a useful tool at predicting the timing of “Early Spring” fungicide applications to suppress dollar spot. To ensure low dollar spot activity a golf course superintendent would make a fungicide application when the pathogen is metabolically active (41-70oF) theoretically before the pathogen reached a level capable of inciting disease. If a fungicide is applied in the early spring once the mean daily air temperature is above 41oF and if fungicide applications continue as recommended by the labeled date rotation until the mean daily air temperatures are above 70oF, a significant reduction in dollar spot severity would likely occur as we observed both years of the study.

Subject Headings

Plant pathology

Keywords

Sclerotinia homoeocarpa; Fungicide; timing; Growing degree days; Turfgrass; Dollar spot; Spring Fall Applications

Committee / Advisors

Michael Boehm (Advisor)
Laurence Madden (Committee Member)
Anne Dorrance (Committee Member)

Pages

92p.

Document number: osu1253625623
Permalink: http://rave.ohiolink.edu/etdc/view?acc_num=osu1253625623

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