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© 2010 Plant Management Network. Early Curative Dollar Spot Control in Creeping Bentgrass as Influenced by Fungicide Spray Volume and Application Timing R. L. Pigati, P. H. Dernoeden, and A. P. Grybauskas, Department of Plant Science and Landscape Architecture, University of Maryland, College Park, MD 20742 Corresponding author: Peter H. Dernoeden. pd@umd.edu Pigati, R. L., Dernoeden, P. H., and Grybauskas, A. P. 2010. Early curative dollar spot control in creeping bentgrass as influenced by fungicide spray volume and application timing. Online. Applied Turfgrass Science doi:10.1094/ATS-2010-0312-03-RS. Abstract The importance of spray volume and application timing of a fungicide targeting dollar spot (Sclerotinia homoeocarpa F. T. Bennett) has been investigated, but with conflicting results. The objectives of this field study were to assess the influence of two spray volumes (468 and 935 liters water/ha) and two application timings (AM to a canopy wet with dew versus PM to a dry canopy) for fungicides targeting dollar spot curatively. Chlorothalonil (8.5 kg a.i./ha), propiconazole (0.5 kg a.i./ha), and a tank-mix of chlorothalonil + propiconazole were compared on fairway height stands of ‘Crenshaw’ (2007 and 2008), ‘Backspin’ (2008), and ‘Providence’ (2009) creeping bentgrass (Agrostis stolonifera L.). There were no spray volume differences in 2007 or 2009. In 2008 in Crenshaw, there was less dollar spot in chlorothalonil-treated plots using the low versus high spray volume, but the opposite occurred in Backspin. Less dollar spot developed in propiconazole-treated plots subjected to the low versus high spray volume in Crenshaw in 2008. Higher levels of dollar spot developed in plots treated with propiconazole in the PM compared to the AM in 2009. The tank-mix of chlorothalonil + propiconazole was unaffected by spray volume or application timing at all sites. The preponderance of data indicated that the curatively applied fungicides generally provided similar levels of dollar spot control at the two spray volumes and application timings evaluated. Introduction Fungicides are commonly used on golf courses to target dollar spot (Sclerotinia homoeocarpa F.T. Bennett) in creeping bentgrass (Agrostis stolonifera L.) and other turfgrasses. Chlorothalonil (tetrachloroisophthalonitrile) is a contact fungicide frequently applied to target dollar spot and is valued for its broad spectrum activity and lack of resistance problems (9). Two application factors that have been shown to impact the effectiveness of fungicides targeting turf diseases are spray volume and application timing (3,4,8). Nozzle type also can influence fungicide performance (7,8). Determining the optimal spray volume and application timing may provide a longer period of dollar spot control, which could lead to less fungicide use. Ashbaugh and Larsen (1), Gregos et al. (6), and Vincelli et al. (10) evaluated the effects of various spray volumes and fungicides targeting dollar spot in one-season studies and found no statistical differences. The aforementioned studies involved both preventive and curative fungicide applications to either putting green or fairway height creeping bentgrass and were previously reviewed (9). In a two-year field study, Kennelly and Wolf (8) found little or no spray volume (i.e., 204, 408, or 814 liters/ha) differences when targeting dollar spot in creeping bentgrass maintained as a putting green with chlorothalonil. Couch (3), however, found a relationship between spray volume and fungicide efficacy when targeting dollar spot curatively in creeping bentgrass with anilizine, chlorothalonil, and iprodione in a one-season study. In a three-year study, McDonald et al. (9) investigated the level of dollar spot control in fairway height creeping bentgrass as influenced by spray volume and application timing. In that study, the acropetal penetrant propiconazole (1-{[2(2,4-dichlorophenyl)-4-propyl-1,3-dioxolan-2-yl]methyl}1-H-1,2,4-triazole), chlorothalonil, and a tank-mix combination of both fungicides were evaluated. They observed that chlorothalonil generally was more effective in controlling dollar spot when applied in the lower (468 liters/ha) versus a higher (1020 liters/ha) spray volume, but the differences were small. Furthermore, chlorothalonil applied to a dry canopy in the PM generally resulted in improved efficacy compared to morning applications with dew present. The performance of propiconazole alone and the propiconazole plus chlorothalonil tank-mix, however, were unaffected by spray volume or application timing. Fidanza et al. (4) reported that the contact fungicide fludioxonil [4-(2, 2-difluoro-1,3-benzodioxol-4-yl)-1H-pyrrole-3-carbonitrile] provided better basal rot anthracnose (Colletotrichum cereale Manns.) control in putting green height Poa annua L. when applied in 814 versus 407 liters/ha. Unpublished studies also suggest that a higher spray volume, which likely would provided better coverage, may be more efficacious when targeting S. homoeocarpa for curative fungicide treatment (M. Fidanza, personal communication). Fungicides initially were applied preventively in the study by McDonald et al. (9), and each fungicide treatment was applied at right angles (i.e., two passes across each plot) rather than in one direction, which probably improved coverage. In the aforementioned study, the two perpendicular passes equaled the rate and water volume being assessed. This study was similar to the investigation reported by McDonald et al. (9), but differed in procedure as follows: (i) fungicide treatments were applied curatively (i.e., post symptom expression) rather than preventively; and (ii) the fungicides were applied in one direction without overlap, which more closely simulates how fungicides are applied professionally on golf courses. Hence, the objectives of this study were to assess the effectiveness of chlorothalonil, propiconazole, and a tank-mix of chlorothalonil + propiconazole when applied in two spray volumes (468 and 935 liters/ha) and two application timings (AM to a canopy wet with dew and PM to a dry canopy) for early curative dollar spot control. The Study Sites and Their Management This field study was conducted at the University of Maryland Paint Branch Turfgrass Research Facility in College Park, MD. Soil was a Keyport silt loam (fine, mixed, semiactive, mesic Aquic Hapludult) with a root zone pH ranging from 5.8 to 6.2 and 12 to 20 mg of organic matter per gram of soil. In 2007, treatments were applied to Crenshaw creeping bentgrass, which was established in September 2006. In 2008, treatments were initiated on two different dates in separate stands of Crenshaw and Backspin creeping bentgrass. The Crenshaw site was established in September 2007, whereas Backspin was established in September 2006. In 2009, a September 2008 seeded stand of Providence was the study site. All study sites generally were mowed three times weekly with a triplex mower to a height of about 12 mm and clippings generally were returned. Study sites were mowed 24 h prior to, but not within 48 h after each fungicide application. Turf was irrigated as needed to prevent drought stress, but water was not applied within 24 h of any fungicide application. Each site received between 100 and 150 kg N/ha from urea in the autumn of each year, but no nitrogen was applied during the study period to any site. Because dollar spot was annually and chronically severe in Backspin and Crenshaw, these sites had received numerous applications of fungicides in previous years. Boscalid {3-pyridinecarboxamide, 2-chloro-N-(4’-chloro [1,1’-biphenyl]-2-yl)}, chlorothalonil, and propiconazole were applied for this purpose. Conversely, the younger Providence site had not received any fungicide applications prior to the time the study was initiated. Dollar Spot Assessment and Statistical Analyses Plots measured 1.2 m by 1.8 m and were arranged in a randomized complete block with four replications. There was a 30-cm creeping bentgrass border between all plots to minimize dew displacement when walking from one plot to another. All data were subjected to analysis of variance (ANOVA) using the SAS Mixed procedure (SAS version 9.1; SAS Institute Inc., Cary, NC). Residuals from the ANOVA were inspected for violations of the assumptions of ANOVA using the SAS Plot procedure. Data were transformed and reanalyzed when necessary. Area under the disease progress curve (AUDPC) data were calculated by the trapezoidal method (2). The AUDPC data did not require transformation. Pairwise comparisons of the effect of spray volumes and timings for each fungicide treatment AUDPC were made with the PDIFF option of the SAS Mixed procedure. Pre-planned orthogonal contrasts were used to test for significant differences between spray volumes and application timings on fungicide performance for each rating date (5). Contrast data were square-root transformed to satisfy the assumption that data were normally distributed, but actual means are used in figures. Dates when significant differences occurred were determined using the F-tests for pre-planned contrasts in SAS Proc-Mixed procedure. Data from untreated plots shown in figures are given for comparison, but were not included in the contrasts. Dollar spot was assessed on a three to four-day interval during each study period by counting the number of S. homoeocarpa infection centers (IC’s) per plot. Plot rating continued 20 to 30 days after the final fungicide application to determine if greater separation of treatments would occur as residual efficacy deteriorated. In 2007, a reapplication threshold was established at 30 IC’s per plot to ensure plots were not severely damaged, but was lowered to 20 IC’s in 2008 and 2009. The threshold was used to time reapplications and was not intended to be used for integrated pest management (IPM) purposes. That is, the thresholds were not intended to mimic acceptable levels of dollar spot control on golf courses. Most golf course superintendents using IPM principles would likely establish an action threshold of < 10 IC’s 2.3/m² for dollar spot. Except in Crenshaw (2008), all three fungicide treatments, which are described below, were applied on the same dates when the threshold was exceeded, which usually occurred in chlorothalonil-treated plots first. Conversely, the fungicides were re-applied to meet each fungicide treatment threshold in Crenshaw in 2008. The Fungicide Treatments and How They Were Applied Chlorothalonil (Daconil Ultrex 87.5 WDG; Syngenta Crop Protection Inc., Greensboro, NC) was applied at a rate of 8.5 kg a.i./ha (3.2 oz product 1000/ft²); propiconazole (Banner MAXX 1.24 ME; Syngenta Crop Protection, Inc., Greensboro, NC) was applied at a rate of 0.5 kg a.i./ha (1.0 fl oz product 1000/ft²); the tank-mix of chlorothalonil plus propiconazole was applied at the aforementioned rates and there was an untreated control. The fungicides were applied at two different times as follows: in the morning with ample dew present in the turf canopy (AM), and in the afternoon when the turf canopy was completely dry (PM). The AM treatments were applied between 0700 and 0800 h and PM treatments were applied between 1200 and 1400 h. All fungicides were applied using a CO2-pressurized backpack sprayer at 262 kPa (35 psi) equipped with two nozzles spaced 46.8 cm (18 inches) apart. During application, the sprayer passed over each plot once, thus simulating the fungicide delivery method used on most golf courses. The sprayer was equipped with two, 8004 or 8008 TeeJet (Spraying Systems, Wheaton, IL) flat-fan nozzles calibrated to deliver fungicides in a water volume of 468 liters/ha (50 gal/acre) or 935 liters/ha (100 gal/acre), respectively. Except for Crenshaw in 2008, fungicides were applied initially when dollar spot was active in low levels (< 5 infection centers per plot). Dollar spot levels were greater (about 10 to 12 infection centers per plot) at the time fungicides were applied in 2008 to Crenshaw. The fungicides were applied at least twice at each site on a 14 to 21-day interval on the dates footnoted in Tables 1 to 4. Spray Volume and Timing Effects in Crenshaw in 2007 Fungicides were applied 9 and 24 July and 10 August 2007 and the threshold was 30 IC per plot. Data collection began on 16 July and ceased on 29 August 2007. The AUDPC data showed no spray volume or application timing differences among treatments in 2007 (Table 1). There were, however, several rating dates when significant contrast differences were observed. Plots treated with propiconazole in the low spray volume developed more IC’s (average = 8 IC’s) compared to the high spray volume (average = 2 IC’s) on the earliest rating dates (i.e., 20, 23, and 27 July), but not thereafter (data not shown). On two late-season rating dates (i.e., 24 and 27 August), chlorothalonil-treated plots subjected to the PM application timing (average = 40 IC’s) had more IC’s compared to plots subjected to the AM application (average 26 IC’s; data not shown). The AM applications of propiconazole resulted in less dollar spot control (average = 7 IC’s) early in the study (i.e., 20 July to 2 August), when compared to PM applications (average = 2 IC’s), but not later (data not shown). There were no significant spray volume or application timing differences on individual rating dates for the chlorothalonil + propiconazole tank-mix in 2007. Table 1. Area under the disease progress curve (AUDPC) values for spray volume and application timing for three fungicide treatments targeting S. homoeocarpa in ‘Crenshaw’ creeping bentgrass in 2007.
x All treatments were applied 9 and 24 July and 10 August 2007. y Probability (α-level) of Type 1 error for mean comparison across columns. Spray Volume and Timing Effects in Backspin in 2008 Fungicides were applied 27 June and 13 July 2008 and the threshold was 20 IC’s per plot. Data collection began 29 June and ceased on 8 August 2008. Only chlorothalonil-treated plots had higher AUDPC values (P = 0.029) in plots treated with the low versus high spray volume (Table 2). There were greater numbers of IC’s on 8 of 17 rating dates prior to and following the second application of chlorothalonil in low versus high spray volume plots (Fig. 1). Table 2. Area under the disease progress curve (AUDPC) values for spray volume and application timing for three fungicide treatments targeting S. homoeocarpa in ‘Backspin’ creeping bentgrass in 2008.
x All treatments were applied 27 June and 13 July 2008. y Probability (α-level) of Type 1 error for mean comparison across columns.
There was one rating date following the initial application (i.e., 11 July) in which there were more IC’s in propiconazole-treated plots subjected to the low (20 IC’s) versus high (7 IC’s) spray volume (data not shown). No significant IC differences were observed between spray volumes following the application of propiconazole. There were no spray volume differences for the chlorothalonil + propiconazole tank-mix applied to Backspin. No AUDPC application timing differences were observed (Table 2). On 13 of 18 rating dates, chlorothalonil plots treated in the PM had more IC’s than AM-treated plots (Fig. 2). Differences between treatments occurred on four rating dates prior to the reapplication of chlorothalonil. Following the second application, dollar spot activity declined for a few days and then increased. More IC’s were observed in PM versus AM plots on 9 rating dates between 15 July and 8 August. There were no differences between AM and PM application timings on individual rating dates in propiconazole or chlorothalonil + propiconazole-treated plots in Backspin.
Spray Volume and Timing Effects in Crenshaw in 2008 Fungicides were applied initially on 17 July 2008 and reapplied on the dates footnoted in Table 3. The threshold was 20 IC’s per plot. Data were collected between 18 July and 15 September. There was a considerable amount of dollar spot (i.e., 10 to 12 IC’s per plot) at the time of the initial application and disease severity was greater in the Crenshaw than Backspin. Unlike what was observed in Backspin, AUDPC values showed that chlorothalonil (P = 0.021) and propiconazole (P = 0.091) performed better when applied in the low spray volume in Crenshaw (Table 3). Table 3. Area under the disease progress curve (AUDPC) values for spray volume and application timing for three fungicide treatments targeting S. homoeocarpa in ‘Crenshaw’ creeping bentgrass in 2008.
w Chlorothalonil was applied 17 and 31 July and 12 August 2008. x Propiconazole was applied 17 July and 4 and 27 August 2008. y Chlorothalonil + Propiconazole was applied 17 July, 4 August and 3 September 2008. z Probability (α-level) of Type 1 error for mean comparison across columns. Significant spray volume differences were detected in chlorothalonil-treated plots on 9 of 25 rating dates (Fig. 3). There were more IC’s in high compared to low spray volume plots on only one date (i.e., 28 July) following the initial application. During the period between the second and third chlorothalonil application, there were no dates in which significant spray volume differences were observed. Chlorothalonil was reapplied a third time on 13 August. On 7 of 8 rating dates between 30 August and 17 September, there were fewer IC’s in plots subjected to the low versus the high spray volume.
No spray volume differences were observed between the first and second propiconazole application. Following the second propiconazole application (i.e., 4 August), there were fewer IC’s in low (average = 5 IC’s) versus high (average = 13 IC’s) spray volume plots (data not shown). Propiconazole was reapplied a third time on 27 August, but no spray volume differences were observed after 20 August. There were no spray volume differences on any date in plots treated with the chlorothalonil + propiconazole tank-mix. There were no AUDPC application timings differences in Crenshaw in 2008 (Table 3). Chlorothalonil provided better dollar spot control when applied in the PM (average = 18 IC’s) versus AM (average = 30 IC’s) on three rating dates between 28 July to 1 August 2008 in Crenshaw, but not on any date before or after (data not shown). Dollar spot levels were lower in AM (average = 10 IC’s) versus PM (average = 18 IC’s) plots treated with propiconazole on five rating dates between 13 and 27 August (data not shown). There were no application timing differences among plots treated with the tank-mix of chlorothalonil + propiconazole. Spray Volume and Timing Effects in Providence in 2009 Fungicides were applied 1 and 23 June and 9 and 28 July 2009 and the threshold was 20 IC’s per plot. Plots were evaluated for disease between 8 June and 7 August. Dollar spot pressure was low from 1 June to 24 July (i.e., 1 to 6 IC’s per plot), but became severe (i.e., > 40 IC’s per plot) for a two week period between 28 July and 7 August. The AUDPC values showed that there were no spray volume differences among treatments in 2009 (Table 4). Among timing treatments, more dollar spot (P = 0.077) developed in PM versus AM plots treated with propiconazole. On 14 July, the only rating date when a significant difference was observed, there was more disease in plots treated with chlorothalonil in the PM (average = 6 IC’s) than the AM (average = 3 IC’s) (data not shown). Table 4. Area under the disease progress curve (AUDPC) values for spray volume and application timing for three fungicide treatments targeting S. homoeocarpa in ‘Providence’ creeping bentgrass in 2009.
x All treatments were applied 1 and 23 June and 9 and 28 July 2009. y Probability (α-level) of Type 1 error for mean comparison across columns. Summary and Recommendations While there were spray volume and application timing differences on individual rating dates, AUDPC values, a representation of disease severity during each test period, revealed no significant effect of spray volume in 2007 or 2009. Chlorothalonil alone and propiconazole alone provided better dollar spot control in the low versus high spray volume in Crenshaw in 2008. Conversely, chlorothalonil alone provided better dollar spot control in Backspin in the high versus low spray volume in 2008. According to AUDPC values, only propiconazole was influenced by application timing in which more disease developed in PM versus AM-treated plots in 2009 (P = 0.077). The chlorothalonil + propiconazole tank-mix was unaffected by spray volume or application timing in all sites and years. Plots were assessed for dollar spot numerous times in 2007 (n = 13); Backspin in 2008 (n = 17); Crenshaw in 2008 (n = 25) and in 2009 (n = 18). Other than those years and cultivars where significant AUDPC values were observed there were relatively few treatment differences on individual rating dates. For example, more dollar spot developed in plots treated in the low spray volume with chlorothalonil on five individual rating dates over all sites and years. Higher levels of dollar spot developed in chlorothalonil plots treated in the AM on three dates in 2008; whereas, more dollar spot developed in PM plots treated with chlorothalonil on two dates in 2007 and one date in 2009. More dollar spot developed in PM-treated propiconazole plots on two dates in 2007. McDonald et al. (9) consistently observed better dollar spot control with chlorothalonil applied in 468 liters/ha in the PM versus 1020 liters/ha in the AM. The magnitude of the differences was small and they concluded that superintendents could apply chlorothalonil in 468 liters/ha just as effectively as in 1020 liters/ha. The current study was designed to evaluate spray volumes and timings similar to McDonald et al. (9), but fungicides initially were applied curatively rather than preventively. Other than chlorothalonil providing improved dollar spot control in Crenshaw using the low spray volume in 2008, chlorothalonil results do not fully support the findings of McDonald et al. (9). Improving spray coverage can enhance dollar spot control with fungicides (11). McDonald et al. (9) applied the fungicides at right angles, which likely improved coverage versus a one direction application. The better coverage using the method employed by McDonald et al. (9) could have impacted chlorothalonil performance more since it is a contact protectant, which will not be taken into tissue and redistributed. Furthermore, McDonald et al. (9) applied fungicides pre-plant infection and did not allow dollar spot to exceed a threshold of 8 to 10 IC’s before a fungicide was reapplied. Hence, the much lower level of disease pressure and likely improvement in fungicide coverage probably accounted for the differences observed between the current and aforementioned study. In general, the performance of propiconazole was similar to that observed by McDonald et al. (9), except improved control was observed with propiconazole applied in the low spray volume in Crenshaw in 2008 and it performed better in the AM versus PM application timing in Providence in 2009. The spray volumes and application timings evaluated did not affect the level of dollar spot control provided by the tank-mix of chlorothalonil + propiconazole in the current study or that reported by McDonald et al. (9). Plots were evaluated for 20 or more days following the final fungicide application to determine if there would be a large separation between treatments as residual effectiveness deteriorated. Data show that while there were many significant differences between treatments on late rating dates the numerical differences were relatively small. These data suggest that the spray volumes and application timings assessed were not dominant factors in dollar spot suppression. Furthermore, it is again noted that Ashbaugh and Larsen (1), Gregos et al. (5), and Vincelli et al. (10) found no spray volume differences for a variety of fungicides targeting dollar spot in one-year field studies. Similarly, in a two-year field study in creeping bentgrass maintained as a putting green, Kennelly and Wolf (8) reported that chlorothalonil generally provided equally effective dollar spot control, regardless of being applied in 204, 408, or 816 liters/ha. Hence, there is no compelling evidence at this time to recommend the use of a higher (i.e., 816 to 935 liters/ha) versus lower (i.e., 408 to 468 liters/ha) spray volume when targeting dollar spot curatively with chlorothalonil, propiconazole or chlorothalonil + propiconazole in fairway height creeping bentgrass. There is, however, overwhelming evidence that the tank-mix of chlorothalonil + propiconazole was unaffected by spray volume or application timing in the current study as well as that reported by McDonald et al. (9). Applying the aforementioned tank mix would preclude any concern about water volume (i.e., 468 or 935 liters/ha) or the presence or absence of dew on the level of dollar spot control for golf course superintendents. The tank mix also was invariably associated with the lowest AUDPC values indicating that it provided improved control compared to either component applied alone. Using a lower spray volume would be advantageous since less water would be used, the time it takes to apply a fungicide would be reduced, and labor and equipment costs would be reduced. Acknowledgments We thank the Eastern Shore Association of Golf Course Superintendents and Mid-Atlantic Association of Golf Course Superintendents for supporting this study. This manuscript is a contribution of the Maryland Agricultural Experiment Station. Literature Cited 1. Ashbaugh, F. M., and Larson, P. O. 1984. Effect of various dilution rates on curative fungicidal control of dollar spot. Fung. Nemat. Tests 38:187. 2. Campbell, C. L., and Madden, L. V. 1990. Introduction to Plant Disease Epidemiology. John Wiley & Sons, New York, NY. 3. Couch, H. B. 1984. Dilution rates, nozzle size, nozzle pressure, and disease control. Golf Course Mgt. 52(8):73-80. 4. Fidanza, M. F., Kaminski, J. E., Agnew, M. L., and Shepard, D. 2009. Evaluation of water droplet size and water-carrier volume on fungicide performance for anthracnose control on annual bluegrass. Intl. Turfgr. Soc. Res. J. 11:195-205. 5. Gomez, K. A., and Gomez, A. A. 1984. Statistical Procedures for Agricultural Research. John Wiley & Sons, New York, NY. 6. Gregos, J. S., Jung, G., and List, B. 2000. Dollar spot volume study for fairway turf. 2000 Wis. Turfgr. Res. Rep. 18:46-47. 7. Kaminski, J. E., and Fidanza, M. A. 2009. Dollar spot severity as influenced by fungicide mode of activity and spray nozzle. HortScience 44:1762-1766. 10. Vincelli, P., Dixon, E., Williams, E., and Burris, P. 2003. Efficacy of fungicides for control of dollar spot of creeping bentgrass managed as a fairway. Fung. Nemat. Tests 59:T007. |
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