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© 2006 Plant Management Network.
Accepted for publication 23 March 2006. Published 31 May 2006.

Dollar Spot Control In Creeping Bentgrass As Influenced by Fungicide Spray Volume and Application Timing

Steven J. McDonald, Graduate Research Assistant, Peter H. Dernoeden, Professor, Department of Natural Resource Sciences and Landscape Architecture, University of Maryland, College Park 20742-3721; and Cale A. Bigelow, Assistant Professor, Department of Agronomy, Purdue University, West Lafayette, IN 47907-2054

Corresponding author: Steven J. McDonald. McDsj@umd.edu

McDonald, S. J., Dernoeden, P. H., and Bigelow, C. A. 2006. Dollar spot control In creeping bentgrass as influenced by fungicide spray volume and application timing. Online. Applied Turfgrass Science doi:10.1094/ATS-2006-0531-01-RS.

Abstract

Dollar spot (DS), caused by Sclerotinia homoeocarpa F. T. Bennett, can be a difficult disease to control in creeping bentgrass (Agrostis stolonifera L.). The objectives of this three-year field study were to: (i) assess the influence of two spray volumes (468 and 1020 liters of water per ha); and (ii) evaluate the impact of the presence or absence of dew at the time of application on the ability of chlorothalonil, propiconazole, and a tank mix of chlorothalonil and propiconazole to control DS in fairway-height creeping bentgrass. Chlorothalonil provided better DS control when applied to a dry canopy after 12:00 h, when compared to AM applications. Chlorothalonil generally provided better DS control when applied in 468 versus 1020 liters of water per ha; however, there were no rating dates when chlorothalonil provided more effective DS control when applied in 1020 liter/ha. On several 2004 rating dates, chlorothalonil applied in the AM with dew displaced provided better DS control than the AM application with dew present. The presence or absence of dew and the two spray volumes assessed did not affect the level of DS control provided by propiconazole or a tank mix of propiconazole and chlorothalonil. The amount of AM dew present in the canopy ranged between 982 and 2,548 liter/ha. Chlorothalonil performance likely was reduced as a result of being diluted or washed from foliar surfaces in the high spray volume or diluted by dew. Since both fungicides performed well when applied in 468 liters of water per ha, golf course managers can use the lower spray volume to save time, labor, and fuel.

Introduction

Dollar spot continues to be a difficult disease to control in creeping bentgrass fairways in many regions. Chlorothalonil (tetrachloroisophthalontitrile) is a contact fungicide and is perhaps the most common chemical used on turf for disease control. Following its re-registration in 1999, the United States Environmental Protection Agency mandated use restrictions on turfgrass (7). Chlorothalonil is highly valued for fungicide resistance management programs and methods for improving its performance need to be investigated. There have been no reported cases of pathogen resistance to chlorothalonil, but there have been resistance problems with other fungicides used to control turfgrass diseases (2,6,7). Propiconazole (1-[[2-(2, 4-dichlorophenyl)-4-propyl-1, 3-dioxolan-2-yl] methyl]-1H-1, 2, 4-triazole) is commonly used to control DS and generally provides a longer period of control than chlorothalonil. Propiconazole penetrates plants and moves mostly acropetally in the xylem.

Due to playability issues, potential pesticide exposure, and demands from golfers, superintendents normally make pesticide applications early in the morning. The effect of the presence of dew at the time a fungicide is applied is unknown. Furthermore, there has been little study on the impact of spray volume (SV) on fungicide performance. Spray volume is the amount of water that a product is dissolved or suspended into before it is applied to a given area of turf. Due to conflicting research results and varying SVs and/or methods of application, further study is needed to evaluate the importance of SV as well as the presence or absence of dew on the ability of fungicides to control DS. Couch (4) evaluated triadimefon (1-(2-(2,4-dichlorophenyl) 4-propyl-1-1,3-dixolan-2-ymethyl-1H-1,2,4- triazole) and chlorothalonil in SVs ranging from 203 to 13,033 liters of water per ha (liter/ha) for curative DS control in creeping bentgrass. Couch (4) observed that chlorothalonil (6.2 kg a.i./ha) performed best in 407 liter/ha. He also reported that triadimefon (0.76 kg a.i./ha) performed best when applied in 815 liter/ha. Vincelli et al. (8) evaluated the efficacy of triadimefon (0.38 kg a.i./ha) and chlorothalonil (8.0 kg a.i./ha) applied in 407 and 815 liter/ha for DS control in creeping bentgrass and reported no significant differences between spray volumes (8). Ashbaugh and Larson (1) applied triadimefon (1.0 kg a.i./ha), iprodione (1.5 kg a.i./ha) (3-(3, 5-dichlorophenyl)-N-(1-methylethyl)-2, 4,-dioxo-1-imidazolidinecarboxamide), and chlorothalonil (4.0 and 8.0 kg a.i./ha) curatively to creeping bentgrass and similarly reported no differences in DS control among SVs (203, 407, 1017.5, and 2035 liter/ha).

Manufacturer labels often are vague, but generally recommend SVs ranging from 204 to 1868 liter/ha. Managers would prefer to utilize lower rather than higher SVs to save time, fuel, and equipment use. Hence, an important aspect of this study was to determine if DS control is diminished if a lower rather than higher spray volume were utilized. The purpose of this study was to investigate the efficacy of a contact (chlorothalonil) and an acropetal penetrant (propiconazole) fungicide for their ability to control DS as influenced by SV (468 and 1020 liter/ha) and by the presence or absence of dew (AM dew present or displaced, and PM dry turf).

Evaluating Spray Volume and Application Timing on Dollar Spot Control

Field studies were conducted from 2002 to 2004 at the University of Maryland Turfgrass Research Facility in College Park, MD. Soil was a Keyport silt loam (fine, mixed, semiactive, mesic Aquic Hapludult) with a pH ranging from 5.8 to 6.2 and 12 to 20 mg of organic matter per gram soil. Treatments were applied with a CO₂ pressurized sprayer (262 kPa) equipped with either an 8004 (468 liter/ha; low SV) or 8010 (1020 liter/ha; high SV) flat fan nozzle. Individual plot size was 1.5 × 1.5 m. This study differed from others since treatments were applied preventively and were not reapplied until threshold levels of DS were observed. The reapplication threshold was subjectively established at 8 to 10 infection centers (ICs) or 0.5% plot area blighted (% PAB). Dollar spot developed naturally and uniformly in all years.

During all years, study sites were fertilized with N at 100 to 150 kg/ha per year and mowed three times weekly (12.7 mm). The study sites generally were mowed about 20 h after treatments were applied. Irrigation was applied continuously due to frequent periods of drought stress in 2002. In 2003 and 2004, however, irrigation was seldom needed because of frequent and abundant rainfall. In all years, AM treatments were applied at 0800 h and PM treatments were applied after the turf canopy was dry, typically after 1230 h. In 2003 and 2004, dew was displaced using the straight edge on the reverse side of an aluminum rake immediately before treatments were applied (Fig. 1). No fungicides were applied to the test sites in the spring prior to the initiation of each study.

Fig. 1. Study site design used in 2003 and 2004. In selected plots, dew was displaced immediately before treatments were applied.

Site Descriptions

In 2002, experiments were conducted on a stand of ‘L-93’ creeping bentgrass which was seeded in fall of 2000. The experiment design was a randomized complete block with four replications. The treatment structure in 2002 was a 2 (SVs) × 2 (AM and PM) × 2 factorial (chlorothalonil and untreated control). Chlorothalonil (Daconil Ultrex 82.5WDG; Syngenta Crop Protection, Greensboro, NC) was applied at 8.0 kg a.i./ha. Spray volumes were 468 liter/ha (low SV) or 1020 liter/ha (high SV). These treatments were applied to separate plots in the PM on the same day. This was the only year when there was a no “dew-displaced” treatment. All dates of application are footnoted in data tables.

In 2003 a stand of ‘Crenshaw,’ seeded in fall of 2001, was used. The rate of chlorothalonil was reduced from 8.0 to 4.5 kg a.i./ha in 2003. The experiment was designed as a completely randomized design with four replications (Fig. 1). The 2003 treatment structure was a 2 (SVs) × 3 (AM, AM dew displaced, and PM dry) × 4 (chlorothalonil, propiconazole (Banner MAXX 1.3EC; Syngenta Crop Protection, Greensboro, NC); tank mix and untreated control) factorial. Fungicide treatments were: chlorothalonil (4.5 kg a.i./ha), propiconazole (3.3 kg a.i./ha), and a tank mix of chlorothalonil and propiconazole (same rates). Spray volumes were 468 or 1020 (liter/ha).

An autumn seeded stand of ‘Southshore’ was the 2004 study site. The experimental design and treatment structure were the same as described for 2003. The rate of propiconazole, however, was reduced from 3.30 to 1.65 kg a.i./ha, when applied alone or tank mixed with chlorothalonil.

Disease Ratings and Treatment Separation

Ratings were obtained twice weekly by counting the number of dollar spot infection centers per plot (ICs) or by estimating the percent of plot area blighted (% PAB) once infection centers coalesced. Percent of plot area blighted was assessed visually on a 0 to 100 scale with 0= no DS and 100= entire plot area blighted. All data were square root transformed to correct for normality, however, actual means are shown in the tables. Area under the disease progress curve (AUDPC) values were calculated using the formula å [ y_i + y_i+1)/2 [ t_i+1-t_i], where i=1, 2, 3….n-1; y_i is the amount of disease (either ICs or % PAB); and t_i is the time of the i^th rating (3). The AUDPC values were calculated separately for early season (i.e., IC data) and late season (i.e., % PAB data) data collection periods. The 2002, 2003, and 2004 % PAB AUDPC values include ratings taken 18, 41, and 23 days after the last fungicide application, respectively. Data were subjected to analysis of variance (ANOVA) and significantly different means were separated at P ≤ 0.05 using Tukey’s least significant difference mean comparison test using the SAS MIXED procedure (5). The ANOVA between fungicide, dew and spray volume and their interactions resulted in the highest level of interactions at fungicide by spray volume. Therefore, to assess this interaction, orthogonal contrasts were used to examine which fungicide(s) were providing a different level of dollar spot control as influenced by spray volume.  There were no other interactions that were consistently observed throughout the study. The pre-planned orthogonal contrasts evaluated were: chlorothalonil applied in the low SV versus high SV; AM dew present versus AM dew displaced; AM dew present versus PM; AM dew displaced versus PM; and propiconazole alone versus propiconazole + chlorothalonil. The contrasts were calculated using estimate statements in the SAS MIXED procedure.

Measuring the Amount of Dew in the Canopy

Canopy dew measurements were obtained as described by Williams et al. (9). Dew was measured over 120 cm² area four times in each untreated control plot using a wooden frame as a template. Data were converted from grams 120/cm² to millimeters of moisture as previously described (9).

The Influence of Spray Volume and Application Timing on Dollar Spot Control in 2002

The 2002 study year was marked by hot, dry weather and high DS disease severity. On 28 June (eight days after treatment), all treatments significantly reduced DS levels, compared to the untreated control (Table 1). At this time, the PM application of chlorothalonil in the low SV provided better DS suppression than both treatments applied in the high SV. Eight days following re-application (i.e., 29 July), all chlorothalonil treatments reduced DS levels dramatically, when compared to the untreated control. Furthermore, on 29 July chlorothalonil applied in the low SV provided better DS control than in the high SV. By 1 August, plots treated with chlorothalonil in the low SV and both timings had trace levels of DS when compared to treatments applied in the high SV and the untreated control. Dollar spot pressure intensified in the following days. On the last rating date (7 August), chlorothalonil applied in the low SV and in the AM or PM continued to provide better DS control, when compared to AM treatments applied in the high SV.

Table 1. Number of Sclerotinia homoeocarpa infection centers as influenced by chlorothalonil application timing and spray volume in ‘L-93’ creeping bentgrass, 2002.

 ^w Treatments were applied 20 June and 21 July 2002 and chlorothalonil was applied at a rate of 8.0 kg a.i/ha.

 ^x Means in the same column followed by the same letter are not significantly different at P < 0.05 according to Tukey’s protected least significant difference test. Data were analyzed using a square root transformation, but data in columns are actual means.

 ^y AM treatments were applied in early morning with dew present on the canopy.

 ^z PM treatments were applied in the afternoon to a dry canopy.

The Influence of Spray Volume and Application Timing on Dollar Spot Control in 2003

In 2003, the rate of chlorothalonil was reduced from 8.0 to 4.5 kg a.i./ha and three new parameters were evaluated as previously described. Data are shown as % PAB since patches coalesced in untreated plots before ICs developed in fungicide-treated plots. There was a significant fungicide effect on most rating dates because propiconazole and the tank mix were providing a higher level of DS control, compared to chlorothalonil alone (data not shown).

Chlorothalonil Alone Spray Volume Treatments, 2003

On 12 of the 21 rating dates, chlorothalonil applied in the low SV provided better DS control when compared to chlorothalonil applied in the high SV (all data not shown). Evaluation of AUDPC indicated that chlorothalonil alone provided better DS control when applied in the PM and in the low SV than AM applications with dew present or displaced or in the high SV (Tables 2 and 3). From 30 July to 11 August, few significant differences or interactions were observed among SVs and application timings (data not shown). Dollar spot peaked on 16 August, when 7.9% PAB was observed in untreated plots (Table 2). On 16 August, chlorothalonil applied in the low SV gave better DS control, when compared to plots treated with the high SV (Table 2 and 3), although both treatments provided good control. On 25 August, chlorothalonil alone applied in the low SV, PM provided better DS control than both AM treatments applied in the high SV (Table 2). From 7 September to 1 October, chlorothalonil applied in the low SV provided better DS control than the high SV (Table 3).

Table 2. Percent plot area blighted by Sclerotinia homoeocarpa as influenced by fungicides, spray volume, and application timing where dew was either present, displaced, or absent in ‘Crenshaw’ creeping bentgrass, 2003.

 ^w Chlorothalonil–alone (4.5 kg a.i./ha) treatments were applied on 23 July, and 7 and 23 August 2003.

 ^x Propiconazole alone (3.3 kg a.i./ha) and propiconazole (3.3 kg a.i./ha) + chlorothalonil (4.5 kg a.i./ha) were applied on 23 July and 19 August 2003.

 ^y Means in the same column followed by the same letter are not significantly different at P < 0.05 according to Tukey’s protected least significant difference test. Data were analyzed using a square root transformation, but data in columns are actual means.

 ^z Dollar spot was rated visually on a 0 to100 scale with 0= no blighting, 0.5% blighted=reapplication threshold and 100= 100% of plot area blighted by S. homoeocarpa.

Table 3. Pre-planned orthogonal contrasts among spray volume, application timing, and fungicide treatments and their effect on dollar spot control in ‘Crenshaw’ creeping bentgrass, 2003.

 ^x Chlorothalonil–alone (4.5 kg a.i./ha) treatments were applied on 23 July and 7 and 23 August 2003.

 ^y Propiconazole alone (Prop, 3.3 kg a.i./ha) and propiconazole (3.3 kg a.i./ha) + chlorothalonil (TM, 4.5 kg a.i./ha) were applied on 23 July and 19 August 2003.

 ^z *, **, ***, and NS refer to the 0.05, 0.01, 0.001 significance levels and non-significant, respectively.

Influence of Dew Displacement in Chlorothalonil-Treated Plots, 2003

There were no differences on any rating date when chlorothalonil was applied in the AM with the dew present versus dew displaced (Table 3). For several rating dates in August and September, chlorothalonil applied in the PM provided better DS control, when compared to AM applications with the dew displaced (Table 3). The AUDPC values showed that chlorothalonil treatments in the low SV applied in AM with dew displaced and in the PM, provided better DS control than both AM treatments in the high SV (Table 2). Within the high SV, PM treatments provided better DS control, when compared to both AM treatments.

Propiconazole and Propiconazole + Chlorothalonil Tank-Mix Treatments, 2003

When comparing propiconazole alone treatments among themselves, few differences were observed throughout 2003 (Table 2, all data not shown). The tank-mix treatments provided better DS control on 9 July compared to propiconazole alone. Propiconazole alone and the tank mix were last applied on 19 August and no differences among application timing or SV treatments were observed thereafter (Table 6). The tank mix provided better DS control than propiconazole on 9 of the 21 rating dates (Table 3, all data not shown).

Influence of Spray Volume and Application Timing on Dollar Spot Control in 2004

In 2003, no differences were observed among propiconazole alone or the tank-mix treatments. Therefore, in 2004 the rate of propiconazole was reduced from 3.30 to 1.65 kg a.i./ha for both treatments.

Chlorothalonil-Alone Spray Volume Treatments, 2004

On 2 June, plots treated with chlorothalonil alone in the low SV, PM had less DS than plots treated in the low SV, AM with dew present or in the high SV with dew present (Table 4). On 13 June (9 DAT), and 15 and 17 June, chlorothalonil alone applied in the low SV provided better DS control, when compared to the high SV (Table 5). Dollar spot was allowed to progress above the threshold following the last application on 23 June. Dollar spot became very severe during the first half of July and, on 9 July, 18.8% PAB was observed in untreated plots (Table 4). Data analyses from 7 to 16 July again showed that chlorothalonil provided better control when applied in the low SV versus the high SV. Hence, on 9 of 18 rating dates in 2004, chlorothalonil applied in the low SV provided better DS control, when compared to treatments applied in the high SV (Table 5).

Table 4. Number of Sclerotinia homoeocarpa infection centers and percent of plot area blighted by S. homoeocarpa as influenced by fungicides, spray volume, and application timing where dew was either present, displaced, or absent in ‘Southshore’ creeping bentgrass, 2004.

 ^w Chlorothalonil–alone (4.5 kg a.i./ha) treatments were applied on 12 May, 4 and 23 June 2004.

 ^x Propiconazole alone (1.65 kg a.i./ha) and propiconazole (1.65 kg a.i./ha) + chlorothalonil (4.5 kg a.i./ha) were applied on 12 May and 18 June 2004.

 ^y Means in the same column followed by the same letter are not significantly different at P < 0.05 according to Tukey’s protected least significant difference test. Data were analyzed using a square root transformation, but data in columns are actual means.

 ^z Dollar spot was rated visually on a 0 to100 scale with 0= no blighting, 0.5% blighted=reapplication threshold and 100= 100% of plot area blighted by S. homoeocarpa.

Table 5. Pre-planned orthogonal contrasts among spray volume, application timing, and fungicide treatments and their effect on dollar spot control in ‘Southshore’ creeping bentgrass, 2004.

 ^× Chlorothalonil–alone (4.5 kg a.i./ha) treatments were applied on 12 May, 4 and 23 June, 2004.

 ^y Propiconazole alone (Prop, 1.65 kg a.i./ha) and propiconazole (1.65 kg a.i./ha) + chlorothalonil (TM, 4.5 kg a.i./ha) were applied on 12 May and 18 June, 2004.

 ^z *, **, ***, and NS refer to the 0.05, 0.01, 0.001 significance levels and non-significant; respectively.

Influence of Dew Displacement in Chlorothalonil-Treated Plots, 2004

Plots treated in the AM with dew displaced had less DS, when compared to plots treated in the AM with dew present (June 2, Table 5). Plots treated in the PM had less DS compared to plots treated in the AM with dew displaced (Tables 4 and 5). On 3, 8, and 11 June, plots treated in the PM had less DS compared to plots treated in the AM with dew present (Table 5).

Chlorothalonil treatments were re-applied on 4 June, when plots had reached the threshold. From 22 June to 2 July, chlorothalonil applied in the PM provided consistently better DS control than plots treated in the AM with the dew displaced (Table 5). During the later stages of the epidemic (7 to 16 July), few differences were observed among application timing or dew treatments (Table 4, all data not shown). On 5 of 18 rating dates, chlorothalonil provided better DS control when applied in the AM with the dew displaced, when compared to the AM application with the dew present. Also, on 8 of 18 rating dates, chlorothalonil provided better DS control when applied in the PM, when compared to AM treatments with the dew present (Table 5).

Propiconazole Alone and Propiconazole + Chlorothalonil Tank-Mix Treatments, 2004

No differences were observed on any 2004 rating date when propiconazole or tank-mix treatments were compared to themselves (Table 4). When DS first was observed in the propiconazole and tank-mix-treated plots between 8 and 11 June, the tank mix had provided better DS control than propiconazole alone (data not shown). Similar results were observed from 22 June to 16 July, and significant contrast differences occurred on 11 of 18 rating dates (Table 5). On each of those dates, plots treated with the tank mix of propiconazole + chlorothalonil had less DS than plots treated with propiconazole alone.

Dew Measurements

Morning (0800 h) dew measurements were obtained on four, rain-free days between 4 June and 22 August in 2003 and 2004. The mean amount of dew quantified was different on each date, which would be expected in view of varying temperatures, relative humidity, and other environmental factors. Dew levels ranged from 982 liter/ha to 2,548 liter/ha, with a mean of 1842 liter/ha (Fig. 2). Williams et al. (9) found that the mean amount of dew on the canopy of fairway height creeping bentgrass was 1,945 liter/ha. Hence, these measurements were very similar to those reported by Williams et al. (9).

Fig. 2. Dew measurements obtained from fairway-height creeping bentgrass in 2003 and 2004.

Summary and Recommendations

To observe differences among treatments, DS was allowed to become active before plots were re-treated to remain within the threshold and to avoid excessive blighting. The magnitude of the differences in DS levels among treatments in these studies was small because a relatively low threshold was established. On 25 of 46 rating dates over the three years, chlorothalonil alone provided better DS control when applied in 468 versus 1020 liter/ha (all data not shown). Furthermore, there were no dates in any year when better DS control was observed in plots receiving chlorothalonil alone applied in the high SV. Couch (4), previously reported that chlorothalonil provided better DS control using a similar SV (i.e., 407 liter/ha), when compared to higher SVs (≥ 814 liter/ha). Other researchers, however, observed that there were no differences in the level of DS control provided by chlorothalonil using various SVs (1,8). Differences among studies could be attributed to disease pressure, preventive versus curative treatment, number or interval of applications, amount of active ingredient, formulation, and other factors. Applying chlorothalonil to a dry canopy in the PM generally increased efficacy, when compared to both AM treatments. In 2003, there were no DS differences on any rating date between AM dew present and displaced treatments using chlorothalonil. On five of sixteen rating dates in 2004, however, chlorothalonil applied in the AM with the dew displaced resulted in better DS control, when compared to AM applications with the dew present. While there was no consistent benefit provided by displacing dew between years, 2004 data suggest that displacing dew can be beneficial when using chlorothalonil alone. It is possible that significant amounts of chlorothalonil did not adhere to the foliage when it was applied in the higher SV (1020 liter/ha) or in the presence of dew (982 to 2,548 liter/ha). Hence, to optimize chlorothalonil performance when targeting DS, it should be applied to a dry canopy in 468 liter/ha rather than 1020 liter/ha.

No differences were observed in the level of DS control in either year among dew and SV treatments using propiconazole alone and propiconazole + chlorothalonil. Evidently, SV and the presence of dew did not affect the ability of effective levels of propiconazole to penetrate plants. During 2003 and 2004 the tank mix, however, provided better and extended levels of DS control on 29 of 39 rating dates, when compared to propiconazole alone (all data not shown). Previous research has shown that chlorothalonil tank mixed with a penetrant can improve the level of DS control, when compared to either fungicide applied alone (6,7).

Data showed that managers can effectively use a 468 liter/ha SV for targeting DS with the fungicides evaluated. This information is very important since using 1020 liter/ha would require about twice the amount of water. Since golf course fairways typically range between 10 and 12 ha, applying fungicides in the higher SV would require the input of substantially more time, labor, fuel, and equipment. These results pertain only to DS control in creeping bentgrass with chlorothalonil and propiconazole applications with a flat fan nozzle. Sclerotinia homoeocarpa initially attacks foliage, but can eventually infect crown tissue. Other turfgrass pathogens that primarily infect stem and/or root tissue may be more efficaciously controlled by fungicides applied in higher SVs.

Acknowledgments

We thank the Mid-Atlantic Association of Golf Course Superintendents and Dr. Michael Agnew of Syngenta Crop Protection for their interest in and financial support of this project.

Literature Cited

1. Ashbaugh, F. M., and Larsen, P. O. 1984. Effect of various dilution rates on curative fungicidal control of dollar spot. Fung. Nemat. Tests. 38:187.

2. Burpee, L. L. 1997. Control of dollar spot of creeping bentgrass caused by an isolate of Sclerotinia homoeocarpa resistant to benzimidazole and demethlation-inhibitor fungicides. Plant Dis. 81:1259-1263.

3. Campbell, C. L., and Madden, L. V. 1990. Introduction to Plant Disease Epidemiology. John Wiley and Sons, New York.

4. Couch, H. B. 1984. Dilution rates, nozzle size, nozzle pressure and disease control. Golf Course Manag.52:73-80.

5. SAS Institute Inc., 2003. SAS OnlineDoc Version 9.1. SAS Institute. Cary, NC.

6. Vargas, J. M. 2004. Management of Turfgrass Diseases, 3rd Ed. CRC Press, Boca Raton, FL

7. Vincelli, P., and Dixon, E. 2003. Summer fungicide spray programs for creeping bentgrass greens. Golf Course Manag. 71:87-90.

8. Vincelli, P., Dixon, E., Williams, D., and Burrus, P. 2003. Efficacy of fungicides for control of dollar spot of creeping bentgrass managed as a fairway. Fung. Nemat. Test 59:T007.

9. Williams, D. W., Powell, A. J., Jr., Vincelli, P., and Dougherty, C. T. 1998. Separation and quantitation of the sources of dew on creeping bentgrass. Crop Sci. 38:1613-1617.