Gray leaf spot, induced by <I>Pyricularia grisea</I>, is a disease of increasing importance in tall fescue in the southeastern United States. Previous research has shown that several herbicides may predispose turfgrasses to some diseases and that certain essential nutrients may have antagonistic effects on fungal plant pathogens. The objectives of this research were to evaluate the effects of herbicide and nutrient treatments on gray leaf spot development in tall fescue. Inoculation techniques were also evaluated for establishing gray leaf spot on tall fescue in controlled environments. Field studies revealed that 2,4-D applications resulted in significantly higher quality turf and lower gray leaf spot incidence than the untreated control. Turf treated with 2,4-D amine + mecoprop + dicamba also exhibited significantly less foliar blight symptoms than the untreated control. In vitro experiments revealed the growth-inhibiting effects of 2,4-D on <I>P. grisea</I> implicated in the field, as mycelial growth was completely inhibited at concentrations of 500 and 1000 mg L<sup>-1</sup>. Colony growth was not affected at 2,4-D concentrations up to 100 mg L<sup>-1</sup>. Phosphorous acid treatments resulted in a reduction in turf quality compared to an untreated control, as did manganese and zinc treatments. Foliar blight caused by P. grisea was substantially increased in H<sub>3</sub>PO<sub>3</sub>-treated plots in 2003, where a 40% difference in blighted turf was observed between plots that received H<sub>3</sub>PO<sub>3</sub> treatments every 14 days and the untreated control. Area under the disease progress curve (AUDPC) analysis also revealed the significant detrimental effects of the phosphorous acid treatments. No significant differences in disease incidence or leaf spot size among nutrient treatments were observed in greenhouse treatments. Isolate selection was a significant factor for disease development and leaf spot size following spray inoculation under optimal environmental conditions. In general, disease incidence increased as inoculum density increased. Placing plants in covered containers or plastic bags immediately following inoculation for a 24-h period also appeared to promote disease development. Seeding rate did not have a significant effect on gray leaf spot development. We conclude that herbicide applications do not predispose tall fescue to gray leaf spot development and that applications of nutrients alone do not suppress development of gray leaf spot in tall fescue. Adjusting cultural practices as additional control measures for gray leaf spot does not appear to be a successful approach to managing this increasingly important disease.
| Identifer | oai:union.ndltd.org:NCSU/oai:NCSU:etd-07082004-113557 |
| Date | 08 July 2004 |
| Creators | Gregg, John Patrick |
| Contributors | Dr. Charles H. Peacock, Dr. H. David Shew, Dr. Lane P. Tredway |
| Publisher | NCSU |
| Source Sets | North Carolina State University |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://www.lib.ncsu.edu/theses/available/etd-07082004-113557/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to NC State University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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