Last updated 6/30/98 |
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Richard Latin
The objective of this research was to compare various fungicide application schedules for efficacy against brown patch on perennial ryegrass.
Brown patch can be a serious problem of perennial ryegrass fairways where the economics of fungicide application signifcantly affect spray decisions. Although the appearance of brown patch has long been associated with hot humid weather of mid summer, using the correlation to assist with the timing of fungicide sprays for fairway turf is only currently being investigated. Weather-based spray programs operate on the premise that they can identify the most appropriate times to spray; therefore no unnecessary fungicide would be applied, resulting in the fewest sprays with acceptable disease control. Previous observations with a published system for brown patch on ryegrass showed that the system overpredicted brown patch outbreaks, resulting in more sprays than necessary. A similar disease warning system is currently being developed at Purdue.
The experimental site was on a mixed stand of perennial ryegrass maintained at 0.75 inch mowing height at the Purdue Agronomy Research Center in West Lafayette, IN. Individual plots measured 3.3 ft x 10 ft (1m x 3m) and were randomized within each of 3 replications. Treatments are listed in Table 14. Initial treatments were applied on 25 June. The turf was inoculated on 26 June with a millet seed (approximately 15 infested grains per plot) culture of Rhizoctonia solani.
Temperature and relative humidity data used in the forecast program were recorded on site with a Rainwise Weatherlog instrument. The forecast program calculates an index value (EFI) that characterizes each day in terms of its favorability for a brown patch outbreak. According to the model, a value of 6 or greater elicits a brown patch warning and a spray advisory. The EFI values recorded throughout the summer of 1997 are presented in Figure 1. Inspection of the figure shows that 3 brown patch favorable periods were identified, 26 June, 2 July, 15 July, 28 July, and 10 August, 21 August.
All fungicide treatments were with Chipco 26019 Flo at a rate equivalent to 4.0 fl oz/M. Applications were made with a bicycle wheel sprayer with 3 nozzle boom that delivered 2 gal/M through Tee-Jet 8004 flat fan nozzles.
Brown patch development was significantly less in the fungicide treated plots than in the untreated plots, with the execption of the 28 day treatment. However, only the fungicide treatment at the 14-day application interval result in less than 10% of the plot affected by disease. The plots sprayed according to the forecast system were sprayed only three times, but did not differ significantly from the plots sprayed at 21-day intervals.
Valid conclusions cannot be drawn from a single experiment. The 1998 research will include a model developed at Purdue that uses the duration of the dew period and the average temperature during the dew period to forecast disease outbreaks.
Table 14. Comparison of fungicidea application schedules for control of brownpatch on perennial ryegrass. |
Brown patch percentage |
Application schedule / (spray dates) |
Aug 1 |
Aug 15 |
| 14-day (Jun 25, Jul 09, Jul 23, Aug 06) | 4.3 | c | 6.1 | b |
| 12-day (Jun 25, Jul 16, Aug 06) | 16.1 | bc | 20.1 | b |
| 28-day (Jun 25, Jul 23) | 28.3 | ab | 42.0 | a |
| Forecast systemb (Jun 25, Jul 16, Jul 30) | 12.6 | bc | 14.3 | b |
| No fungicide | 38.3 | a | 55.6 | a |
| a All fungicide applications were made with Chipco 26019 FLO
at 4 fl oz/M. b The forecast system was developed by Fidanza et al. at the University of Maryland. |
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