© 2003 Plant Management Network.
Dollar Spot in Four Bentgrass Cultivars as Affected by Acibenzolar-S-Methyl and Organic Fertilizers
Joon Lee, Graduate Research Assistant, University of Florida, Gainesville, FL 32611; Jack Fry, Professor, Department of Horticulture, Forestry, and Recreation Resources, Kansas State University, Manhattan, KS 66506; and Ned Tisserat, Professor, Department of Plant Pathology, Kansas State University, Manhattan, KS 66506
Lee, J., Fry, J., and Tisserat, N. 2003. Dollar spot in four bentgrass cultivars as affected by acibenzolar-s-methyl and organic fertilizers. Online. Plant Health Progress doi:10.1094/PHP-2003-0626-01-RS.
Golf course superintendents are interested in identifying ways to reduce fungicide inputs on creeping bentgrass (Agrostis palustris Huds.) putting greens. Our objectives were to evaluate the influence of the plant defense activator acibenzolar-S-methyl (ASM, Actigard, Syngenta Corp., Basel, Switzerland) and organic fertilizers on dollar spot (Sclerotinia homoeocarpa F.T. Bennett) and brown patch (Rhizoctonia solani Kuhn) in four bentgrass cultivars. Crenshaw had over 10 times the area under the disease progress curve (AUDPC) value for dollar spot compared to the cultivar L-93 in 2000. Acibenzolar-S-methyl applied at 35 g a.i. per ha every 14 days between mid-May and mid-September for two consecutive growing seasons reduced the number of S. homoeocarpa infection centers by 15% in Crenshaw, 24% in Penncross, and 29% in Providence, but had no effect on the number of infection centers in L-93. Only Sustane (Crenshaw in 2000) and Milorganite (Crenshaw and Providence in 2001) suppressed dollar spot compared to urea. The following fertilizers resulted in an increase in S. homoeocarpa infection centers: Nature Safe 8-1.3-4.2 in Crenshaw in both years, and in Providence in 2000; Nature Safe 10-0.9-6.6 in Crenshaw in both years; and Sustane with Iron in Crenshaw in 2001. All other organic fertilizer x cultivar combinations resulted in dollar spot levels equivalent to those observed in urea-treated turf. Brown patch levels were not affected by cultivar, ASM, or organic fertilizers. The defense activator ASM deserves further evaluation as a tool to reduce dollar spot-targeted fungicide inputs in creeping bentgrass.
Golf course superintendents are interested in identifying ways to reduce fungicide use on creeping bentgrass greens. One such way is to select cultivars wisely. Settle et al. (11) found that Crenshaw was highly susceptible to dollar spot, L-93 displayed good resistance, and Penncross and Providence were intermediate. Use of L-93 afforded greater flexibility in disease control strategies, and reduced total fungicide input. Similarly, inclusion of Crenshaw in blends of bentgrass cultivars increased dollar spot in Texas; whereas, use of L-93 reduced dollar spot levels (1). More information is needed regarding cultivar responses to alternative disease control strategies.
Acibenzolar-S-methyl is a plant defense activator that is reported to induce systemic acquired resistance in plants and has been shown to have antifungal, antibacterial, and antiviral activity (4). The chemical has no known direct antifungal properties (7). In the only work done with ASM on bentgrass, the number of S. homoeocarpa infection centers in a blend of Cato:Crenshaw (50:50) was reduced by 38%; however, disease pressure was high, and turf quality was unacceptable through much of the study period (8). No information is available on the possible differences in the disease response of bentgrass cultivars to ASM application.
Reports of disease suppression following application of organic fertilizers, or top-dressings, have been inconsistent. Nelson and Craft (9,10) evaluated various composts and organic fertilizers as amendments to topdressings for the biological control of brown patch and dollar spot, and found that some suppressed disease. Similarly, Boulter et al. (2) suppressed dollar spot in creeping bentgrass with multiple compost applications during the growing season. Nevertheless, dollar spot in compost-treated plots was still extensive (up to 33% of the turf blighted). Creeping bentgrass fertilized with urea in Pennsylvania had equal or better turf quality and dollar spot suppression compared to that receiving natural organic fertilizers (6).
In Maryland (5), nine N sources were applied to fairway-height Southshore creeping bentgrass over six years, and dollar spot was evaluated the last three years. One organic N source suppressed dollar spot, and another enhanced it. The remainder seemed to have no effect on dollar spot relative to urea. As with ASM, no research has been done to compare differences among bentgrass cultivars to potential disease-suppressing effects of organic fertilizers.
It was our hypothesis that combining the use of a relatively disease resistant bentgrass cultivar (e.g., L-93 for dollar spot resistance) with cultural practices that may reduce disease incidence (i.e., a plant defense activator and/or organic fertilizers) may be a successful approach to reducing fungicide inputs on bentgrass putting greens. Our objective was to evaluate dollar spot and brown patch incidence, and turf quality, of four creeping bentgrass cultivars treated with ASM and organic fertilizers.
This study was initiated in May, 2000 on a sand-based USGA green at the Rocky Ford Turfgrass Research Center in Manhattan, KS. The root zone contained 95% sand and 5% clay, and had a pH of 7.5. Turf was mowed six days weekly at 4 mm and irrigated to prevent stress by applying approximately 5 mm water daily. No fungicides were applied to the study area. Plot design was a split-strip plot with three replications. Whole plots were the bentgrass cultivars (Crenshaw, L-93, Penncross, and Providence) that measured 8 m ◊ 2 m. Strip-plots were application of the plant defense activator, ASM (treated or untreated), and measured 8 m ◊ 1 m. Sub-plots were fertilizer treatments that measured 1 m ◊ 2 m. Creeping bentgrass cultivars had been growing on the study area since Fall, 1996. From 1997 to 1999, a fungicide test had been conducted in this area (11). To reduce the impact of the previous yearís fungicide treatments, no applications were made between September, 1999 and May, 2000. Statistical randomization also limited potential effects of earlier fungicide treatments on results of this study.
Application of Acibenzolar-S-Methyl and Organic Fertilizers
Acibenzolar-S-methyl was applied at 35 g a.i. per ha in water at 815 liter/ha on a 14-day interval between 5 May and 8 September, 2000, and 20 April and 7 September, 2001 using a CO2-powered sprayer pressurized to 138 kPa.
Organic fertilizers and urea were applied using a shaker bottle to provide N at 50 kg/ha on 25 May, 29 September, and 27 October, and N at 25 kg/ha on 22 June, 20 July, and 17 August in 2000; N at 50 kg/ha on 18 April, 2 May, and 12 September, and N at 25 kg/ha on 6 June, 11 July, and 8 August in 2001. Fertilizers evaluated, analyses (N-P-K), and their composition as described by the manufacturers were: Milorganite (6-0.9-0), activated sewage sludge; Nature Safe (8-1.3-4.2) (Griffin Industries, Inc., Cold Spring, KY), hydrolyzed feather, meat, bone, and blood meals, langbenite, yeast sugars, carbohydrates, and humus; NatureSafe (10-0.9-6.6), same manufacturer and contents as NatureSafe 8-1.3-4.2; Roots Turf Food (15-1.3-6.6), plant and animal meals; Sustane (10-0.4-1.7) (Natural Fertilizer of America, Inc., Cannon Falls, MN), aerobically composted turkey litter; Sustane with Iron (5-0.9-3.3), same manufacturer and contents as Sustane 10-0.4-1.7; and urea (46-0-0), synthetic organic N.
Data Collection and Analysis
Data were collected on dollar spot and brown patch incidence, and turf quality, every two weeks from 10 May to 14 September, 2000 and 23 May to 20 September, 2001. Sclerotinia homoeocarpa infection centers were counted inside a 27-cm-diameter template that was arbitrarily tossed two times per plot. Values were then converted to number of infection centers per square meter. Percentage of each plot infested with brown patch was rated visually using a 0 to 100% scale. Dollar spot and brown patch data were analyzed using Area Under the Disease Progress Curve (AUDPC) that allows comparison of treatments using a whole-season data summary (3). Turf performance in bentgrass treated with organic fertilizers is compared to that of turf receiving urea for purposes of discussion.
Turf quality was rated visually once weekly on a 0 to 9 scale, where 0 = dead turf; 7 = acceptable quality for a putting green; and 9 = optimum color, density, and uniformity. Data were subjected to analysis of variance, and means separated using a Fisherís protected LSD test (P < 0.05).
Cultivar and ASM Effects on Dollar Spot and Brown Patch
Dollar spot and brown patch were observed in both years. Average dollar spot AUDPC values for cultivars over fertilizer and ASM treatments for 2000 and 2001, respectively, were as follows: Crenshaw, 10515 and 1647; L-93, 1158 and 176 ; Penncross, 1954 and 216; and Providence, 1823 and 464. As such, Crenshaw had nearly ten times greater AUDPC levels than L-93 in 2000. Ranking of cultivars with regard to dollar spot susceptibility was similar to that described by Settle et al. (11). Brown patch levels exceeded 50% of the plot area affected within some plot areas in 2000 and 2001. However, there were no effects of cultivar, ASM, or organic fertilizers on brown patch.
A significant cultivar ◊ ASM (P < 0.01) interaction was observed for dollar spot. The plant defense activator, ASM, reduced (P < 0.05) the number of S. homoeocarpa infection centers by 15% in Crenshaw, 24% in Penncross, and 29% in Providence when averaged over both years. Only L-93 did not exhibit a significant reduction in dollar spot in response to ASM applications. Figures 1 and 2 illustrate the progression of dollar spot in ASM-treated and nontreated Crenshaw and L-93, respectively. The reduction in dollar spot observed following ASM application in this test, and in earlier work (8), suggests that additional research may be in order to define its potential role in a fungicide-reduction program. At present, ASM is not labeled for use on turf.
Organic Fertilizer Effects on Dollar Spot and Brown Patch
Ultimately, our goal was to identify organic fertilizers that resulted in lower dollar spot levels across cultivars than urea. A significant (P < 0.01) cultivar ◊ fertilizer interaction was observed. Only Sustane (Crenshaw in 2000) and Milorganite (Crenshaw and Providence in 2001) suppressed (P < 0.05) dollar spot compared to urea. The following fertilizers resulted in an increase (P < 0.05) in S. homoeocarpa infection centers as measured by AUDPC: Nature Safe (8-1.3-4.2) in Crenshaw in both years, and in Providence in 2000; Nature Safe (10-0.9-6.6) in Crenshaw in both years; and Sustane with Iron in Crenshaw in 2001. All other organic fertilizers resulted in dollar spot AUDPC levels equivalent to those observed in urea-treated turf, regardless of cultivar. Landschoot and McNitt (6) similarly observed that Penncross creeping bentgrass fertilized with urea in Pennsylvania had equal or better turf quality and dollar spot levels compared to that receiving natural organic fertilizers, including Ringer Commercial Greens Super (feather meal, blood meal, wheat germ, bone meal, liquid fat, D-limonene, and potassium sulfate), Ringer Compost Plus (wheat midds, calcium carbonate, dried molasses, bone meal, urea, and liquid fat) , Sustane , Milorganite, and Harmony (poultry manure). In Maryland (5), Ringer Lawn Restore (a poultry waste product) and urea delayed the development of dollar spot in fairway-height Southshore creeping bentgrass for three consecutive years. Compro (a composted sewage sludge) enhanced dollar spot. None of the fertilizers was associated with higher levels of soil microbial activity.
Most cultivars exhibited unacceptable quality ratings throughout the study period regardless of ASM or N source treatment as a result of high dollar spot pressure. None of the organic fertilizers provided quality superior to urea-treated turf in any cultivar on any rating date. Across all fertilizer and ASM treatments, cultivars and the respective percentage of rating dates on which acceptable quality occurred was: Crenshaw, 6%; L-93, 30%; Penncross, 17%; and Providence, 18%.
Acibenzolar-S-methyl suppressed dollar spot by in all cultivars except L-93, and at levels from 15 to 24%. Acibenzolar-S-methyl may someday be a tool that superintendents could use to reduce fungicide requirements on creeping bentgrass greens. There was no effect of ASM on brown patch; as such, use of ASM in any disease reduction program must account for possible brown patch infestations. We hypothesized that the use of a moderately dollar spot-resistant cultivar such as L-93, in combination with ASM and organic fertilizers, might provide acceptable creeping bentgrass quality with no fungicide input. However, the use of L-93 in combination with ASM and organic fertilizers did not provide satisfactory dollar spot control. Clearly, in our climate where dollar spot pressure can be significant, acceptable bentgrass putting green quality cannot be maintained by employing any of the treatment combinations we evaluated without fungicides.
Thanks are extended to the Kansas Golf Course Superintendentís Association and the Kansas Turfgrass Foundation who helped to sponsor this project.
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