Research Update: Disease Management by Christian Baldwin, Ph.D. L-93 is generally regarded by golf course superintendents as the gold standard in dollar spot resistance. For example, researchers at Rutgers University stated L-93 was least susceptible to dollar spot across various nitrogen and cutting height treatments. Also, the number of fungicide applications were reduced 75% to 88% for L-93 compared to the most susceptible cultivars. The focus of this document is L-93 disease management. Topics include fungicide selection, curative vs. preventative approaches, fungicide spray volumes, disease control without fungicides, and timing of fungicide applications. RESEARCH SUMMARY Curative vs. Preventative Approach Environmental conditions, fungicide selection, disease type, fungicide timing, and application methods appear to influence the effectiveness of a curative approach vs. a preventative approach in controlling diseases on L-93 creeping bentgrass. Absence of Fungicides Without fungicide use, L-93 had greatest dollar spot resistance, Penncross and Providence was intermediate, while Crenshaw was most susceptible. Application of calcium silicate appears to have little effect in minimizing brown patch and dollar spot outbreaks in L-93 creeping bentgrass. Picture of L-93 course Timing and Spray Volumes An effective strategy to minimize the severity of dollar spot on L-93 and to optimize the effectiveness of chlorothalonil, it appears using low spray volumes in the absence of dew minimizes dollar spot severity compared to high spray volumes. Fungicides In a favorable dollar spot environment, L-93 creeping bentgrass requires five chlorothalonil applications, while Penncross and Providence requires seven, and Crenshaw requires eight applications for acceptable season-long dollar spot control. Only L-93 creeping bentgrass had season-long dollar spot control with reduced fungicides rates (chlorothalonil), while Penncross, Providence, and Crenshaw required greater fungicide rates for similar levels of dollar spot control. Triadimefon (0.8 kg a.i. ha -1 /80.9 lb ac -1 ) + flutolanil (4.6 kg a.i. ha -1 /5.9 lb ac -1 ) applied preventative on L-93 every 28 days nearly suppressed all dollar spot outbreaks. Iprodione (3.1 kg a.i. ha -1 /11.8 lb ac -1 ) and iprodione (3.1 kg a.i. ha -1 /11.8 lb ac -1 ) + fosetyl-al (9.9 kg a.i. ha -1 /3.5 lb ac -1 ) applied preventatively in 14-d intervals suppressed dollar spot on L-93. Dollar spot outbreaks in L-93 were reduced by applying azoxystrobin (0.3 kg a.i. ha -1 /0.5 lb ac -1 ) + triadimefon (28 day interval application), triadimefon+ flutolanil (28 day interval application), iprodione (14 day interval application), and iprodione + fosetyl-al (14 day interval application). Fungicide programs that included chlorothalonil, mancozeb, fosetyl-al, and azoxystrobin were the most effective in controlling dollar spot and brown patch in L-93 creeping bentgrass. www.jacklin.com Ph: 1-800-688-SEED fax: 1-509-319-3181 e-mail: info@jacklin.com
Which is the best disease management approach: Preventative or Curative? A preventative program is the strategic application of fungicides prior to anticipated disease symptoms. A curative program approach waits until the appearance of disease symptoms, and then the infected area is treated. An advantage of using a curative program is the potential to reduce the number of fungicide applications compared to a preventative program. Two studies compared preventative and curative fungicide approaches in disease management of L-93 creeping bentgrass. More information about each study is listed in the fungicide programs to control dollar spot and brown patch in L-93 creeping bentgrass section. Royals et al. (2005) noted using a curative approach for disease control consistently resulted in unacceptable turfgrass quality during summer months when disease pressure was greatest. However, a curative approach may be more effective during a more favorable growing season for bentgrass, such as fall or spring, as recuperative ability of L-93 from disease damage would be greater than during stressful summer months. Meanwhile, Settle et al. (2001) noted a curative approach was equally as effective as a preventative approach in controlling dollar spot; however, a curative approach did not successfully control brown patch. Take-home message It appears environmental conditions, fungicide selection, disease type, fungicide timing, and application methods appear to influence the results of utilizing a curative approach vs. a preventative approach in controlling diseases. Royals, J.K. II, S. Bruce Martin, J.J. Camberato, and S.N. Jeffers. 2005. Development and evaluation of strategic fungicide programs for control of warm weather diseases in creeping bentgrass. International Turfgrass Society Research Journal. 10(Part 1):237-246. Settle, D., J. Fry, and N. Tesserat. 2001. Dollar spot and brown patch fungicide management strategies in four creeping bentgrass cultivars. Crop Sci. 41:1190-1197. Non-fungicide approach to minimizing dollar spot and brown patch severity on L-93 creeping bentgrass Dollar spot can be controlled through fertility and cultural practices, but in most cases, dollar spot is commonly controlled through fungicide programs. While fungicides are the primary avenue for dollar spot control, strains of the pathogen (Sclerotinia homoeocarpa) causing dollar spot are beginning to show signs of resistance to certain fungicides. Also, each year, the Environmental Protection Agency (EPA) reviews all existing fungicide labels. The EPA has already recommended the removal of certain popular fungicides, reduced application rates and increased spray intervals for fungicides commonly used in the turfgrass market. In response to this, researchers are currently seeking alternative means for dollar spot control. In an attempt to minimize fungicide requirements for disease control on L-93 creeping bentgrass, researchers at Kansas State University investigated the potential of silicon to minimize disease outbreaks on L-93 creeping bentgrass. In other studies, silicon has been show to be somewhat effective in reducing gray leaf spot on St. Augustinegrass. In another study, researchers in North Carolina showed moderate brown patch and dollar spot reductions on creeping bentgrass when potassium silicate was applied, in place of a fungicide. The mechanism behind silicon s role in disease suppression remains largely unclear. One possible explanation is that silicon prevents fungal penetration by forming a thickened cellulose membrane (double cuticle layer). Another explanation is that silicon increases antifungal compounds which degrade fungal and bacterial cell walls. Regardless, research determining the effectiveness of silicon as a disease reducing nutrient is a relatively new concept. To further explore the potential of silicon minimizing fungicide requirements on L-93 creeping bentgrass, Kansas State researchers determined the effectiveness of calcium silicate (CaSiO3) in suppressing dollar spot and brown patch on an L-93 creeping bentgrass putting green. This project was conducted at Kansas City Country Club in Mission Hills, KS on L-93 creeping bentgrass maintained as a putting green. CaSiO3 was applied at 2440 or 4880 kg ha -1 (2176 or 4353 lb ac -1 ). Before CaSiO3 treatments, the green was core aerified (2-cm diameter, 8-cm deep tines), then the CaSiO3 was applied, and then the area was topdressed with sand. In the CaSiO3 treated plots, silicon concentration in leaf tissue increased and depending on the date measured, higher CaSiO3 application rates led to greater silicon concentrations in leaf tissue. Overall, no reduction in brown patch severity was noted between untreated and CaSiO3 treated plots, regardless of rate. Interestingly, in mid-august, brown patch severity was significantly greater in plots treated with CaSiO3 compared to non-casio3 treated plots. The researchers did not detect a reduction in dollar spot outbreaks between silicon treated and untreated plots. 2
Take-home message Although L-93 creeping bentgrass is capable of accumulating silicon is leaf tissue following soil incorporation of CaSiO3, this accumulation does not appear to minimize dollar spot or brown patch disease pressure. Zhang, Q., J. Fry, K. Lowe, and N. Tesserat. 2006. Evaluation of calcium silicate for brown patch and dollar spot suppression on turfgrasses. Crop Sci. 46:1635-1643. Controlling dollar spot on L-93 creeping bentgrass fairways: When is the best time to spray fungicides? What is the most appropriate spray volume? Researchers at the University of Maryland in College Park, MD conducted field studies to investigate the impact spray volume and dew presence had on the efficacy of chlorothalonil (daconil) in controlling dollar spot on a L-93 creeping bentgrass fairway. Treatments included two flat fan nozzles (8004 and 8010) and two spray volumes of 468 and 1020 L ha -1 (51 and 109 gal ac -1 ). Chlorothalonil was applied at 8.0 kg a.i. ha -1 (8.6 lb ac -1 ) either in the morning with dew present or in the afternoon with no dew present. At the end of June, applying chlorothalonil in the absence of dew with low spray volumes showed greater dollar spot control compared to the higher spray volume treatments. By August, as dollar spot severity was greatest, chlorothalonil applied with low spray volumes with or without dew present continued to show better dollar spot control than high spray volumes with dew present. Therefore, it appears an effective strategy to minimize the severity of dollar spot and to optimize the effectiveness of chlorothalonil, low spray volumes without the presence of dew provides better dollar spot control. Take-home message Based on this study, lower spray volumes were more effective in controlling dollar spot than higher spray volumes. Therefore, golf course superintendents with L-93 creeping bentgrass fairways have the potential to save on labor, time, and fuel costs due to a lower spray volume requirement for dollar spot control. McDonald, S.J., P.H. Dernoedon, and C.A. Bigelow. 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. Fungicide programs to control dollar spot and brown patch in L-93 creeping bentgrass Primary diseases that affect creeping bentgrass include Pythium blight, brown patch, Rhizoctonia leaf spot, dollar spot, fairy rings, and anthracnose. There are many fungicides available for turfgrass managers to minimize outbreaks of many common diseases (Table 1). Therefore, determining which combination of fungicides and the timing of fungicide applications is important information for golf course superintendents with creeping bentgrass putting greens. The following two studies were conducted in warm humid regions of the country, where bentgrass is poorly adapted. A three-year study was conducted in Manhattan, KS at Kansas State University to determine fungicide management strategies to minimize the outbreak of dollar spot on L-93, Crenshaw, Providence, and Penncross creeping bentgrass maintained at putting green standards. Treatments included: Year I Triadimefon (Bayleton) (0.8 kg a.i. ha -1 /80.9 lb ac -1 ) + flutolanil (ProStar) (4.6 kg a.i. ha - 1/5.9 lb ac -1 ) were applied monthly from end of June to beginning of October, Iprodione (Chipco 26GT) (3.1 kg a.i. ha -1 /11.8 lb ac -1 ) was initially applied as dollar spot symptoms were evident and then applied preventatively in 14-d intervals, Iprodione (3.1 kg a.i. ha -1 /11.8 lb ac -1 ) + Fosetyl-Al (Chipco Signature 80WG) (9.9 kg a.i. ha -1 /3.5 lb ac -1 ) were applied preventatively in 14 day intervals. Year II Similar to year I, except; Azoxystrobin (Heritage) (0.3 kg a.i. ha -1 /0.5 lb ac -1 ) + triadimefon (0.8 kg a.i. ha -1 /80.9 lb ac -1 ) were applied every 28 days beginning mid-may through end of September. Year III Chlorothalonil (Daconil) (9.6 kg a.i. ha -1 /10.4 lb ac -1 ) replaced iprodione as the curative application treatment every 14 days, Chlorothalonil was also applied at low rates (2.3 kg a.i. ha -1 /2.5 lb ac -1 ) weekly, 3
Triadimefon rate increased to 1.6 kg a.i. ha -1 (161.9 lb ac -1 ) and applied monthly, All fungicides in year III were applied from end of May to end of September. In year I, triadimefon (0.8 kg a.i. ha -1 /80.9 lb/ac -1 ) + flutolanil (4.6 kg a.i. ha -1 /5.9 lb ac -1 ) applied preventative on L-93 every 28 days nearly suppressed all dollar spot outbreaks. Meanwhile, L-93, Penncross, and Providence required two iprodione applications, while Crenshaw required three applications for season-long dollar spot control. In year II, without fungicide use, L-93 had greatest dollar spot resistance (least amount of infection centers), Penncross and Providence had intermediate resistance, while Crenshaw was most susceptible. Applying azoxystrobin + triadimefon (28 day interval application), triadimefon+ flutolanil (28 day interval application), iprodione (14 day interval application), and iprodione + fosetyl-al (14 day interval application) suppressed dollar spot in Penncross, Providence, and L-93. Meanwhile, L-93 required four iprodione applications, Penncross and Providence required five iprodione applications, while Crenshaw required six applications for season long dollar spot control. In year III, dollar spot outbreaks were greatest compared to year I and II. Regardless, L-93 had lowest dollar spot severity compared to Penncross, Providence, and Crenshaw without fungicide use. Applying chlorothalonil at low rates (2.3 kg a.i. ha -1 /2.5 lb ac -1 ) every 7 days provided near complete dollar suppression only in L-93. This weekly low rate failed to reduce dollar spot outbreaks to adequate levels in Penncross, Providence, or Crenshaw. Across the entire season, L-93 required only five curative chlorothalonil applications, while Penncross and Providence required seven, and Crenshaw required eight for season-long dollar spot control. Another study in Florence, SC evaluated additional fungicide programs for dollar spot and brown patch control on an L-93 creeping bentgrass putting green. A complete list of fungicide treatments and timing is listed in tables 2 and 3. Overall, program 2 and 5 provided greatest control of brown patch, while program 5 was best for dollar spot control. These two programs included azoxystrobin, fosetyl-al, chlorothalonil, or mancozeb. Meanwhile, disease control using program 7 was the poorest in controlling brown patch. Programs with poor disease control are likely attributed to the time of season the fungicide was applied or the interval between applications was too long. Take-home message Planting L-93 provided best dollar resistance in non-fungicide treated plots compared to Penncross, Crenshaw, and Providence. In each of the three years, L-93 consistently required fewer fungicide inputs to minimize dollar spot outbreaks. For optimal disease control management, critical factors influencing the effectiveness of a fungicide program include applying the fungicide at the right time of year and ensuring accurate spray intervals are utilized. Royals, J.K. II, S. Bruce Martin, J.J. Camberato, and S.N. Jeffers. 2005. Development and evaluation of strategic fungicide programs for control of warm weather diseases in creeping bentgrass. International Turfgrass Society Research Journal. 10(Part 1):237-246. Settle, D., J. Fry, and N. Tesserat. 2001. Dollar spot and brown patch fungicide management strategies in four creeping bentgrass cultivars. Crop Sci. 41:1190-1197. 4
Table 1. Trade name, formulation, common name, class, mode of action, and target disease of common fungicides used to control problematic disease in warm, humid regions where L-93 creeping bentgrass is planted (adapted from Royals et al., 2005). Trade Name/ Formulation Common Name Class Mode of Action Target Disease Banner Maxx 1.3 ME Propiconazole Triazole Impairs membrane function by inhibiting ergosterol biosynthesis Dollar Spot Chipco Signature 80WG Fosetyl-Aluminum Phosphonate Disrupts amino acid metabolism Summer Decline Chipco 26GT 2 SC Iprodione Dicarboxamide Impairs DNA synthesis Dollar Spot and Cleary 3336 4L Thiphanate methyl Benzimidazole Blocks nuclear division by interfering with microtubule assembly Dollar Spot and Consyst Thiphanate methyl + chlorothalonil Benzimidazole + nitrile As noted in separate active ingredients Dollar Spot and Daconil Ultrex 82.5 WG Chlorothalonil Benzonitrile Unspecific inhibition of amino acid synthesis Eagle 40WP Myclobutanil Triazole Impairs membrane function by inhibiting ergosterol biosynthesis Dollar Spot and Dollar Spot Fore 80WP Mancozeb Ethylene bisdithiocarbamate Unspecific inactivation of SH groups in amino acids Heritage 50WG Azoxystrobin QoI Inhibits mitochondrial respiration Prostar 70WP Flutolanil Carboxanilide Inhibits succinate dehydrogenase in fungal respiration 5
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