Control Of Dollar Spot Research Articles

Spo0A-dependent antifungal activity of a plant growth promoting rhizobacteria Bacillus subtilis strain UD1022 against the dollar spot pathogen (Clarireedia jacksonii)

Dollar spot is an economically important foliar disease of turfgrass caused by Clarireedia spp. Increased use of chemical fungicides for disease management has possible negative effects on the environment and human health. The quest for eco-friendly alternatives to fungicides is driving the development of new biological strategies for managing dollar spot. In the present study, an analysis of antifungal activity of the plant growth promoting rhizobacteria (PGPR) Bacillus subtilis strain UD1022 (hereafter UD1022) and plant health products (PHPs) (Acibenzolar-S-methyl, kelp extract, fosetyl-Al, and trinexapac-ethyl) against Clarireedia jacksonii for control of the turfgrass fungal disease dollar spot was conducted. In vitro assays revealed that UD1022 has significant inhibitory effects against the mycelial growth of C. jacksonii. Of all the treatments, wild type UD1022 and a non-ribosomal peptide mutant (sfp¯) showed potential antagonism against C. jacksonii with inhibition rate of 17.2 % and 18.4%, respectively. Interestingly a Bacillus-derived broad antifungal compound (surfactin) and PHPs showed no direct antagonistic activity against dollar spot pathogen and were statistically like the untreated control. All the mutants of UD1022 except spo0A¯ showed varying but significant inhibition of the fungal pathogen suggesting that spo0A gene may be directly involved in the antagonism against C. jacksonii. Bacterial volatile compounds (BVCs) of UD1022 may not be involved in antagonism as no fungal inhibition was observed in the indirect assay using split petri plates. Filter sterilized cell free lysate (CFL) as well as heat treated CFL of UD1022 bacterial culture did not show any fungal inhibition indicating a primary role of live bacterial cells and not bacterial-derived or secreted compounds in fungal growth inhibition. The results indicate UD1022 to possess the potential to be extended for the biocontrol of dollar spot of turfgrass.

Comparative physiological and transcriptome analysis provide insights into the inhibitory effect of 6-pentyl-2H-pyran-2-one on Clarireedia jacksonii

Clarireedia spp. is a destructive phytopathogenic fungus that causes turf dollar spot of bent-grass, leading to widespread lawn death. In this study, we explored the antifungal capability of 6-pentyl-2H-pyran-2-one (6PP), a natural metabolite volatilized by microorganisms, which plays an important role in the biological control of turfgrass dollar spot. However, the mechanisms by which 6PP inhibits Clarireedia jacksonii remain unknown. In the present study, C. jacksonii mycelial growth was inhibited by the 6PP treatment and the 6PP treatment damaged cell membrane integrity, causing an increase in relative conduc-tivity. Furthermore, physiological and biochemistry assay showed that 6PP treatment can enhance reactive oxygen species (ROS) levels, malondialdehyde (MDA) content obviously increased with 6PP exposure, increased alchohol dehydrogenase (ADH) and depleted acetalde-hyde dehydrogenase (ALDH), and activated the activities of many antioxidant enzymes in C. jacksonii. Gen Ontology and Kyoto Encyclopedia of Genes and Genomes analysis revealed that some genes in C. jacksonii after 6PP treatment related to integrity of the cell wall and membrane, and oxidative stress were significantly downregulated. It is worth mentioning that the fatty acid degradation pathway is significantly upregulated, with an increase in ATP content and ATP synthase activity, which may promote fungal cell apoptosis. Moreover, we found that the expression of ABC transporters, and glutathione metabolism encoding genes were increased to respond to external stimuli. Taken together, these findings revealed the potential antifungal mechanism of 6PP against Clarireedia spp., which also provides a theoretical basis for the commercial utilization of 6PP as a green pesticide in the future.

Reducing Pesticide Risk Associated With Dollar Spot Management on Golf Course Turfgrass

Pesticides are critical tools for golf course managers to maintain healthy and economically profitable golf course playing surfaces. However, the intensity and types of pesticides used on golf courses can be harmful to human and environmental health. Two separate studies were conducted at two locations in Wisconsin, USA between 2014 and 2020 to test the ability of reduced risk fungicide programs to control dollar spot (Clarireedia spp.) on golf course fairways and putting greens. Risk of the pesticide application programs was quantified in both studies using the active ingredient application rate, the Environmental Impact Quotient (EIQ), hazard quotient (HQ), and the Pesticide Risk Tool (PRT). The first study found that using the Smith-Kerns Dollar Spot Prediction Model to schedule fungicide applications did not reduce pesticide risk on its own, but that a pesticide program utilizing reduced risk products was just as effective in controlling dollar spot as a conventional program while reducing pesticide risk by ~50–80% depending on the pesticide risk indicator used. The second study established an average pesticide risk using HQ based on the pesticide records of 23 randomly selected Wisconsin golf courses. This statewide average was then used to test pesticide programs at 100, 75, 50, and 25% of the average risk for their efficacy in controlling dollar spot over a 4-year period. In the 4 years of the study, dollar spot severity of the 25% risk treatment was statistically indistinguishable from the other three programs. Taken together, these results indicate that pesticide risk can be significantly reduced on golf courses in the US Midwest without sacrificing dollar spot control.

Novel action thresholds of a logistic regression model to forecast dollar spot on bentgrasses

AbstractDollar spot (Clarireedia jacksonii) susceptibility varies among bentgrasses (Agrostis spp.). This trial assessed the ability of five action thresholds of the risk index (RI) of a logistic regression model to forecast dollar spot incidence on bentgrass fairway turf grown on a sandy loam in North Brunswick, NJ. Dollar spot incidence was assessed over 128 observation periods (May to Nov. annually) over 3 yr and related to five action thresholds for prediction accuracy. Action thresholds included a RI threshold of 20% (RI 20%), interpreting the change in the RI over time (RI slope), adjusting the RI upwards to maximize accuracy (RImax), combining RI 20% with RI slope, and combining RImax with RI slope. The RI 20% accurately predicted disease on 63 to 66% of observation periods for highly susceptible creeping bentgrass (A. stolonifera L.) cultivars Shark, Penncross, and Independence; other action thresholds improved accuracy by only 10% or less for these cultivars. Prediction accuracy on lower susceptibility cultivars (007, Declaration, and colonial bentgrass Capri; A. capillaris L.) was substantially improved with four novel action thresholds by reducing over‐predictions compared to RI 20%. Accuracy was improved by as much as 32% when the RImax and RI slope were combined for Declaration compared to RI 20%. On low susceptibility cultivars, turf managers may be able to use action thresholds that incorporate a RI greater than 20% and/or RI slope to reduce fungicide inputs and maintain acceptable dollar spot control compared to RI 20%.

Utilizing organic amendments for general suppression of dollar spot on creeping bentgrass turf

AbstractDollar spot (Clarireedia spp.) negatively impacts the aesthetic value and playability of golf course fairways. A 2‐yr field trial was conducted to examine organic amendment effect on dollar spot severity and on fungicide residual efficacy for dollar spot control on creeping bentgrass (Agrostis stolonifera L. ‘007’). Treatments were arranged in a 7 × 5 split‐plot factorial measuring the effect of fertilizer source (soil incorporated organic biosolids compost, soil incorporated biochar, surface applied organic biosolids compost, surface applied biochar, vermicompost extract, standard fertilizer, or non‐treated) on control of dollar spot by five fungicide treatments (fluazinam 14 d, fluxapyroxad 14 d, fluazinam threshold, fluxapyroxad threshold, none) applied at product label rates. Nitrogen fertility levels for all treatments were standardized at ∼205 kg N ha–1 annually. Threshold fungicide treatments were applied when three or more infection centers per area were counted on two or more of four trial replicates. In 2017, all fertilizer treatments were significantly more effective at reducing disease than non‐treated, but were statistically similar. In 2018, biochar, vermicompost, and standard fertilizer treatments were significantly more effective than organic biosolids compost and non‐treated. Fungicides controlled dollar spot when applied every 14 d. In 2017, all fertilizer treatments reduced the number of threshold sprays compared to none, yet the same effects were not consistently observed in 2018. Study results illustrate the effectiveness of nitrogen application for mitigating dollar spot disease on creeping bentgrass during establishment compared to no fertilizer, potentially allowing for reduced fungicide use to control the disease.

Evaluating biological and oil‐based fungicides for dollar spot suppression on turfgrass

AbstractDollar spot (caused by Clarireedia jacksonii) receives more fungicide applications than any other turfgrass disease. Increasing restrictions on fungicide usage and expanding reports of fungicide resistant fungal populations have resulted in renewed interest in biological and plant‐based control of turfgrass diseases. Six commercially available biological fungicides (Actinovate AG, Double Nickel LC, Nortica, Rhapsody, Serende Opti, Zio) and two oil‐based fungicides (Civitas, Timorex Gold) were evaluated for dollar spot control on a creeping bentgrass putting green in Madison, WI, USA in 2017 and 2018. No biological or oil‐based fungicide provided effective full‐season dollar spot control compared to the synthetic fungicide boscalid. However, Civitas mineral oil provided levels of dollar spot control similar to boscalid on 9 of 12 rating dates over both years. The remaining treatments tested provided levels of dollar spot control and turf quality similar to boscalid ranging from 4 to 7 of a possible 12 rating dates. These results indicate that the biological fungicides tested here failed to provide commercially acceptable dollar spot control under moderate disease pressure in the midwestern U.S. The mineral oil Civitas did provide effective suppression under moderate disease pressure, while the tea tree oil Timorex Golf did not. Certain oil‐based fungicides like Civitas can provide effective dollar spot control during periods of low to moderate disease pressure, but more research is needed before biological fungicides can be successfully integrated into a dollar spot management program.

Resistance risk assessment for fludioxonil in Sclerotinia homoeocarpa in China

Sclerotinia homoeocarpa causes dollar spot disease on turfgrass and is a serious problem on many species worldwide. Fludioxonil, a phenylpyrrole fungicide, is not currently registered for dollar spot control in China. In this study, the baseline sensitivity to fludioxonil was established using an in vitro assay for 105 isolates of S. homoeocarpa collected from 10 locations in different regions of China. Results indicate that the frequency distribution of effective concentration for 50% inhibition of mycelial growth (EC50) values of the S. homoeocarpa isolates was unimodal (W = 0.9847, P = .2730). The mean EC50 value was 0.0020 ± 0.0006 μg/ml with a range from 0.0003 to 0.0035 μg/ml. A total of 7 fludioxonil-resistant mutants were obtained in laboratory, the mutants were stable in fludioxonil sensitivity after the 10th transfer, with resistance factor (RF) ranging from 4.320 to >13,901.4. The mutants showed a positive cross-resistance between fludioxonil and the dicarboximide fungicide iprodione, but not propiconazole, fluazinam, and thiophanate-methyl. When mycelial growth rate, pathogenicity and osmotic sensitivity were assessed, the mutants decreased in the fitness compared with their parental isolates. Sequence alignment of the histidine kinase gene Shos1 revealed a 13-bp fragment deletion only in one mutant, no mutations were observed on Shos1 in the rest resistant mutants.

In Vitro Fungicide-Insensitive Profiles of Sclerotinia homoeocarpa Populations from Pennsylvania and the Surrounding Region.

Repeated fungicide applications are typically required to provide adequate control of dollar spot on golf courses and may shift Sclerotinia homoeocarpa populations from sensitive to insensitive or resistant to an active ingredient. The objective of this study was to characterize the geographic distribution of fungicide-insensitive, fungicide-resistant, and multiple fungicide insensitive (MFI) S. homoeocarpa populations on golf courses in Pennsylvania and the surrounding region. S. homoeocarpa isolates (n = 681) were collected from 45 different golf courses or research facilities. Each isolate was evaluated in vitro against propiconazole, iprodione, boscalid, and thiophanate-methyl using discriminatory concentrations of 0.1, 1.0, 1,000, and 1,000 µg of active ingredient per milliliter of PDA, respectively. Relative mycelial growth (RMG) values were used to determine sensitivity or insensitivity based on comparison with a baseline population. Of the 681 isolates evaluated, 81, 80, and 85% exhibited reduced sensitivity to boscalid, iprodione, and propiconazole, respectively. A total of 41% of the isolates were resistant to thiophanate-methyl. Based on mean RMG of all isolates from each golf course, 16, 35, and 37 of the 45 golf courses exhibited reduced sensitivity to boscalid, iprodione, and propiconazole, respectively. A total of 585 isolates (86%) exhibited an MFI profile in which they were insensitive or resistant to at least two fungicides evaluated. Isolates with reduced sensitivity to boscalid, iprodione, and propiconazole, but sensitive to thiophanate-methyl, were the most common phenotype within the three-MFI profile. Fungicide insensitivity and resistance to commonly used fungicides, as well as MFI profiles, were prevalent in Pennsylvania and the surrounding areas and may cause management challenges.

Development and validation of a weather-based warning system to advise fungicide applications to control dollar spot on turfgrass.

Dollar spot is one of the most common diseases of golf course turfgrass and numerous fungicide applications are often required to provide adequate control. Weather-based disease warning systems have been developed to more accurately time fungicide applications; however, they tend to be ineffective and are not currently in widespread use. The primary objective of this research was to develop a new weather-based disease warning system to more accurately advise fungicide applications to control dollar spot activity across a broad geographic and climactic range. The new dollar spot warning system was developed from data collected at field sites in Madison, WI and Stillwater, OK in 2008 and warning system validation sites were established in Madison, WI, Stillwater, OK, Knoxville, TN, State College, PA, Starkville, MS, and Storrs, CT between 2011 and 2016. A meta-analysis of all site-years was conducted and the most effective warning system for dollar spot development consisted of a five-day moving average of relative humidity and average daily temperature. Using this model the highest effective probability that provided dollar spot control similar to that of a calendar-based program across the numerous sites and years was 20%. Additional analysis found that the 20% spray threshold provided comparable control to the calendar-based program while reducing fungicide usage by up to 30%, though further refinement may be needed as practitioners implement this warning system in a range of environments not tested here. The weather-based dollar spot warning system presented here will likely become an important tool for implementing precision disease management strategies for future turfgrass managers, especially as financial and regulatory pressures increase the need to reduce pesticide usage on golf course turfgrass.

Effect of Oriental Mustard (Brassica juncea) Seed Meal for Control of Dollar Spot on Creeping Bentgrass (Agrostis stolonifera) Turf

This research evaluated oriental mustard [Brassica juncea (L.) Czern.] seed meal (MSM) for safety and efficacy in control of dollar spot (Sclerotinia homoeocarpa F.T. Benn.) in vitro and on creeping bentgrass (Agrostis stolonifera L.) turf. As a plant residual, MSM is the seed fraction that remains after seeds are crushed and oil is removed. The meal contains both nitrogen and secondary compounds termed glucosinolates. When moist, glucosinolates convert to fungicidal isothiocyanates. The in vitro study determined that MSM at higher rates completely suppressed S. homoeocarpa mycelial growth. A field study was conducted for 2 yr with three sequential applications of MSM at seven rates ranging from 0 to 1680 kg ha−1, in addition to the fungicide iprodione at 3.1 kg a.i. ha−1. In 2007, the severity of dollar spot infections varied among MSM treatments, with greater rates reducing dollar spot up to 82% compared with untreated control. In 2008, MSM at 1680 kg ha−1 reduced dollar spot by 60% or greater 8 to 14 wk after initial application (WAIA). After application of MSM at 1120 kg ha−1 or greater, the color of creeping bentgrass color was reduced 1 point on a 1 to 9 scale, but this reduction in color only lasted for 2 wk, and turf color in treated plots increased significantly by 6 WAIA compared with the untreated plots. Collectively, our results suggest that MSM is an organic material that could be integrated into a dollar spot management program on turf for minimizing selection of pathogen resistance to fungicides.

Dollar Spot Control in a Creeping Bentgrass Golf Green with Two Commercial Products Based on Microbial Fermentation and Micronutrients

Dollar spot (caused by Sclerotinia homoeocarpa F.T. Bennett) is one of the most important diseases affecting creeping bentgrass (Agrostis stolonifera L.) golf course greens. The objective of this research was to test two commercial products for dollar spot control, one based on microbial fermentation and the other a micronutrient, comparing their control level with a synthetic fungicide (iprodione). The test was made over two dollar spot‐infected creeping bentgrass greens in autumn 2014 and summer 2015. In both experiments, the products inhibited the normal development of the disease at some point, although iprodione achieved a better control.

Influence of simulated rainfall on efficacy of fluazinam, chlorothalonil and iprodione for dollar spot control in creeping bentgrass

Efficacy of foliar applied fungicides following simulated rainfall for the control of dollar spot (caused by Sclerotinia homoeocarpa F.T. Bennett) was assessed in a two-year field study on creeping bentgrass (Agrostis stolonifera L.) turf maintained as a golf course fairway. The study was conducted as a randomized complete block design with a factorial arrangement. Fluazinam (0.8 kg a.i. ha−1), chlorothalonil (3.79 kg a.i. ha−1) or iprodione (1.5 kg a.i. ha−1) were applied, then subjected to simulated rainfall (2.54-mm) at intervals of 15-, 30-, 60-min post-application, or no simulated rain. In most cases, simulated rainfall occurring ≤60 min post-application had greater disease than no rain plots; however, few differences occurred among rainfall intervals ≤60 min. Fluazinam provided the greatest dollar spot reduction regardless of simulated rainfall interval throughout the study. Chlorothalonil was most susceptible to losses in efficacy due to simulated rainfall, resulting in the greatest disease incidence of those fungicides evaluated. Iprodione was comparable to chlorothalonil during high disease pressure, although during moderate disease pressure it controlled dollar spot for approximately 7 days before disease increased in plots receiving simulated rain compared to those without simulated rain. These data demonstrate that efficacy of fungicides applied for dollar spot control are affected by rain, and differ in their ability to control disease following post-application rain events. Fluazinam, a recently introduced contact fungicide for use on turfgrass, can provide improved control compared to chlorothalonil or iprodione when rain is eminent.

Effect of watered-in demethylation-inhibitor fungicide and paclobutrazol applications on foliar disease severity and turfgrass quality of creeping bentgrass putting greens

Preventive, watered-in applications of DMI fungicides provide control of several soilborne turfgrass diseases on golf putting greens. The objectives of this two-year field study were to determine the impact of these applications on foliar diseases, and evaluate the impact of application timing of paclobutrazol, a plant growth regulator, on disease severity and turfgrass quality. Triadimefon (1.58 kg a.i. ha−1), tebuconazole (0.82 kg a.i. ha−1), metconazole (0.43 kg a.i. ha−1), and triticonazole (0.64 kg a.i. ha−1), were applied twice in late April and May and immediately watered in to the soil profile with 5 mm of post application irrigation. Paclobutrazol (0.28 kg a.i. ha−1) was applied alone, in a tank-mix with the fungicide application, 7 days or 14 days after the fungicide application. Overall dollar spot severity, assessed as area under the disease progress curve (AUDPC), was significantly lower in fungicide treated plots than non-treated plots in both trial years. The date of threshold symptom observation (≥5 infection centers per plot), however, was not different between fungicide treated and non-treated plots in 2011. Triadimefon treated plots had lower AUDPC values than other fungicide treatments. Brown patch severity was not significantly different among treatments. Paclobutrazol applied alone did not reduce dollar spot or brown patch severity, however, paclobutrazol + fungicide treatments resulted in lower dollar spot severity than plots treated with fungicide alone. Short-lived phytotoxicity (bronze discoloration) was observed in plots treated with triadimefon or paclobutrazol + fungicide. Spring preventive fungicide applications targeted at soilborne disease control also provided residual control of dollar spot in this study.

Regulation with Trinexapac-ethyl and Dew Removal at the Time of Fungicide Application Did Not Influence Dollar Spot Control

Dollar spot, caused by Sclerotinia homoeocarpa F.T. Bennett, is an important disease of creeping bentgrass (Agrostis stolonifera L.) on golf courses in the northern United States. Canopy moisture in the form of dew plays an important role in the development of dollar spot and routine displacement has been shown to reduce disease severity. The use of plant growth regulators (PGRs) is a common management practice for maintaining creeping bentgrass fairways, but their influence on dollar spot is unclear. The objective of this field study was to elucidate the influence of dew removal at the time of fungicide application on dollar spot control in creeping bentgrass regulated by trinexapac-ethyl (TE). Main factors in the study included three dew removal strategies (non-treated, dew removed–mowed, and dew removed–not mowed) before the application of four fungicide treatments (non-treated, chlorothalonil, propiconazole, and iprodione). All fungicide treatments were applied once to turfgrass previously treated with TE or not treated. The presence or absence of dew at the time of fungicide application generally had no influence on fungicide performance with respect to dollar spot control. Based on the results of this study, dew removal before the application of fungicides targeting dollar spot is unnecessary. Applications of TE before fungicides reduced dollar spot severity in some cases, but reductions in symptom expression were limited and did not result in markedly improved dollar spot control.

혼용된 2종의 살균제 살포 농도 및 간격에 따른 잔디 동전마름병 방제효과

Dollar spot caused by Sclerotinia homoeocarpa F.T. Benn. is a common and economically important turfgrass disease in South Korea. Fungicides mixture (propiconazole 25% + boscalid 47%) treatments, showing synergistic interaction, with three application rates (low: 50.3 ml 10a -1 and 97.5 g 10a -1 , intermediate: 67.0 ml 10a -1 and 130.0 g 10a -1 , and high: 100.5 ml 10a -1 and 195.0 g 10a -1 ) and two application intervals (10 and 15 days) were evaluated for control of dollar spot in creeping bentgrass golf course putting green. In both nontreated plots of field A and B, the disease has severed as 48.3 and 60.0% after the pathogen inoculation. Two fungicide mixture treatments showed significantly higher the disease control effect than a single fungicide treatment (propiconazole). Field A which showed more the disease severity but the fungicide still showed acceptable level of the disease efficacy (89.0%), significant differences in control value were not detected among treatments. The results suggest that the lower application rate of two fungicides mixture treatments may reduce the dollar spot disease severity in creeping bentgrass golf course putting green.

Mowing Frequency and Plant Growth Regulator Effects on Dollar Spot Severity and on Duration of Dollar Spot Control by Fungicides.

Management of dollar spot (incited by Sclerotinia homoeocarpa) on golf course fairways is increasingly challenging. The objectives of this study were to determine the influence of mowing frequency and plant growth regulators (PGRs) on dollar spot severity and on the residual efficacy of fungicides for control of dollar spot. Two 4-month-long studies were conducted on 'Putter' creeping bentgrass (Agrostis stolonifera) maintained as a fairway at the University of Connecticut. Treatments were arranged in a three-by-three-by-five factorial that assessed the influence of mowing frequency (2, 4, or 6 days week-1) and PGRs (paclobutrazol, trinexapac-ethyl, or none) on dollar spot control by five fungicide treatments (boscalid, chlorothalonil, iprodione, propiconazole, or none). Turf was mowed in the afternoon hours to minimize the confounding effect of mowing frequency on leaf wetness duration. Treatments were initiated in the late spring of 2007 and 2008, and each fungicide treatment was reapplied only when dollar spot exceeded a threshold of five infection centers plot-1. In the absence of fungicides, dollar spot severity was reduced by 63 to 90% in plots treated with paclobutrazol and by 13 to 55% in plots treated with trinexapac-ethyl. Dollar spot severity was 23 to 50% lower in plots mown 2 days week-1 compared with those mown 6 days week-1. In cases where a significant interaction was observed between mowing frequency and PGRs, dollar spot was reduced on most rating dates in plots treated with trinexapacethyl that were mown 2 days week-1 compared with those mown 6 days week-1. Survival analysis of days until threshold was met revealed that duration of control of fungicides in plots receiving paclobutrazol were 28 to 84% longer compared with plots not receiving PGR. Duration of control by fungicides was generally similar between plots treated with trinexapac-ethyl and no PGR. In general, mowing frequency did not influence duration of control. Results from this study indicate that paclobutrazol could be used to increase the treatment interval of fungicides and that mowing frequency in the absence of dew is likely to have little influence on fungicide residual efficacy. When used without fungicides, PGRs and less frequent mowing may reduce dollar spot in situations where fungicide use is limited.

Effects of Dew Removal and Mowing Frequency on Fungicide Performance for Dollar Spot Control.

Dollar spot (Sclerotinia homoeocarpa) is a severe disease problem on creeping bentgrass (Agrostis stolonifera) fairways. The objective of this study was to evaluate the effects of dew removal and mowing frequency on fungicide performance for dollar spot control. In 2009 and 2010, an experiment involving daily dew removal or no dew removal, mowing frequency (2, 4, and 6 days week-1), and fungicides (chlorothalonil, propiconazole, and iprodione) was conducted on creeping bentgrass maintained as a fairway. Daily dew removal resulted in fewer dollar spot infection centers (IC) compared with not removing dew during late summer 2009 and 2010 for all mowing-frequency and fungicide treatments. As mowing frequency increased from 2 to 6 days week-1, dollar spot IC decreased when averaged across all fungicide treatments. For all fungicides, daily dew removal increased the number of days needed to reach a 15-IC plot-1 point of reference when compared with fungicide treatments in which dew was not removed. The number of days required to reach 15 IC varied with fungicide, mowing frequency, and year the test was conducted. Results demonstrate that dollar spot control with fungicides can be extended when daily dew removal is employed and, in some cases, when mowing frequency is increased on dew-covered turf. Benefits of dew-removal practices on dollar spot and fungicide performance can vary with weather conditions, fungicide, threshold level, and possibly other factors.

Simulated Rainfall and Mowing Impact Fungicide Performance When Targeting Dollar Spot in Creeping Bentgrass.

In this 2-year field study, four chemically diverse fungicides (i.e., chlorothalonil, boscalid, iprodione, and propiconazole) were evaluated for their ability to control dollar spot (Sclerotinia homoeocarpa) in creeping bentgrass (Agrostis stolonifera) as affected by simulated rain and mowing timing. Simulated rain (25 to 32 mm) was imposed about 30 min after fungicide application and was compared to rain-free plots. One set of plots was mowed in the morning when the canopy was wet with dew and compared to plots that were mowed when the canopy was dry in the afternoon. The percent reduction in dollar spot control associated with simulated-rain versus rain-free treatments in 2007 and 2008, respectively, was as follows: chlorothalonil 67 and 83%; propiconazole 42 and 79%; boscalid 48 and 70%; and iprodione 33 and 66%. When disease pressure was low, all fungicides subjected to simulated rain provided effective dollar spot control for 7 or more days following the initial application in each year. Across all fungicide-treated plots over 2 years, the average percent reduction in dollar spot associated with morning mowing ranged from 54 to 65%. The reduction in dollar spot severity in morning-mowed plots improved the performance of all fungicides.

Early Curative Dollar Spot Control in Creeping Bentgrass as Influenced by Fungicide Spray Volume and Application Timing

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.

Effect of Nozzle Type and Water Volume on Dollar Spot Control in Greens-Height Creeping Bentgrass

A field study was conducted in 2007 and 2008 to determine the influence of nozzle type and water volume on the control of dollar spot of greens-height creeping bentgrass, caused by Sclerotinia homoeocarpa F. T. Bennett. The nozzles utilized were XR, TurfJet, Air Induction, Turbo TwinJet, and Turbo Drop Twin Fan, all producing flat spray patterns. For each nozzle type, three flow rates were used to produce water carrier volumes equivalent to 0.5, 1.0, or 2.0 gal/1000 ft². Chlorothalonil (1.8 oz/1000 ft²) was applied on a 14-day interval. Disease was assessed by counting the number of dollar spot infection centers in plot centers where spray coverage was complete. Overall, all nozzles except for TurfJet provided similar dollar spot suppression, and water volume was rarely a factor. On one rating date in 2007, all nozzle-volume combinations reduced dollar spot compared to untreated turf except for the TurfJet nozzles at the lower water volumes. On one date in 2008, all nozzle and volume combinations reduced dollar spot compared to untreated turf, with the exception of plots receiving fungicide through XR and TurfJet nozzles at 0.5 gal/1000 ft² or Air Induction nozzles at 1.0 gal/1000 ft². Therefore, the use of a reduced water volume and an air induction drift reducing nozzle may be a practical option for managing dollar spot with a contact fungicide in creeping bentgrass.