Turfgrass Disease Diagnosis: Past, Present, and Future

Turfgrass is a multibillion-dollar industry severely affected by plant pathogens including fungi, bacteria, viruses, and nematodes. Many of the diseases in turfgrass have similar signs and symptoms, making it difficult to diagnose the specific problem pathogen. Incorrect diagnosis leads to the delay of treatment and excessive use of chemicals. To effectively control these diseases, it is important to have rapid and accurate detection systems in the early stages of infection that harbor relatively low pathogen populations. There are many methods for diagnosing pathogens on turfgrass. Traditional methods include symptoms, morphology, and microscopy identification. These have been followed by nucleic acid detection and onsite detection techniques. Many of these methods allow for rapid diagnosis, some even within the field without much expertise. There are several methods that have great potential, such as high-throughput sequencing and remote sensing. Utilization of these techniques for disease diagnosis allows for faster and accurate disease diagnosis and a reduction in damage and cost of control. Understanding of each of these techniques can allow researchers to select which method is best suited for their pathogen of interest. The objective of this article is to provide an overview of the turfgrass diagnostics efforts used and highlight prospects for disease detection.

Potential of NanoPro to reduce fungicide rate for control of Microdochium nivale on an annual bluegrass (Poa annua) green

This is a report on the potential of NanoPro™ to reduce the rate of two commonly used fungicides for control of Microdochium patch (Microdochium nivale), the economically most important turfgrass disease in Scandinavia. The experiment was conducted from 14 Sept. 2018 to 1 May 2019 on an annual bluegrass golf green at the NIBIO Turfgrass Research Center Landvik. Use of NanoPro™ at a rate of 292 ml/ha in tank mixture with the systemic fungicide Delaro® SC 325 or/and the contact fungicide Medallion® TL produced the same level of disease control with a 30-60% reduction in fungicide dosage as with full fungicide dosage without additive. NanoPro™ was more effective with Medallion® TL than with Delaro® SC 325. We conclude that NanoPro™ may have a big potential in Scandinavia and other countries where authorities require reduced fungicide use. The experiment should be repeated one more year before giving final recommendations.

The Association Between In Vitro Propiconazole Sensitivity and Field Efficacy of Five New England Sclerotinia homoeocarpa Populations

Dollar spot (Sclerotinia homoeocarpa) is a major turfgrass disease requiring fungicide application to maintain acceptable conditions for golf. A 2-year field experiment was conducted to determine the association between field efficacy of propiconazole and in vitro fungicide sensitivity of isolates from five S. homoeocarpa populations. Four golf courses with prior propiconazole exposure (Hartford Golf Club, Hickory Ridge Country Club, Shuttle Meadow Country Club, and Wintonbury Hills Golf Club), and a baseline site with no prior propiconazole exposure (Joseph Troll Turf Research Facility) were chosen as field sites. Experimental plots at each site received the following treatments at 21-day intervals: untreated, propiconazole (0.44, 0.88, 1.32, and 1.76 kg a.i. ha–1), and chlorothalonil (8.18 kg a.i. ha–1). S. homoeocarpa isolates were sampled at three time points during 2009 and 2010: initial (directly before fungicide treatment), 7 days after treatment (DAT), and 21 days after the last treatment. Isolates sampled from dollar spot infection centers at 7 DAT (2009 and 2010) were considered to exhibit “practical field resistance”. In parallel, S. homoeocarpa isolates from each site were assayed for in vitro sensitivity to propiconazole by determining relative mycelium growth percentages (RMG%) on potato dextrose agar amended with propiconazole at a discriminatory concentration of 0.1 μg a.i. ml–1. S. homoeocarpa isolates from the four exposed populations displayed significantly higher RMG% values than the baseline population. In general, field efficacy at all propiconazole rates tested was lower at the four locations with prior propiconazole exposure when compared with the baseline population. Increased RMG% values on the propiconazole discriminatory concentration 0.1 μg a.i. ml–1 were associated with decreased relative control values for all propiconazole rates in 2009 and 2010. Results suggest RMG values above 50% at the propiconazole discriminatory concentration of 0.1 μg a.i. ml–1 may be a suitable threshold for detection of S. homoeocarpa isolates that cause practical DMI field resistance.

Simulations of Fungicide Runoff Following Applications for Turfgrass Disease Control

Computer simulations of fungicide loading in surface water runoff were conducted with fungicides commonly used in golf course fairways and lawns in Kentucky. For all fungicides, values for degradation half-life and organic carbon partition coefficient were obtained from published sources; other input parameters were selected to simulate conditions typical in local swards. Spray programs were tested using a 21-year period of weather data for Lexington, KY. Predicted amounts of fungicide in runoff were determined, and predicted fungicide concentrations in runoff (mg/liter) were compared with 50% lethal concentration (LC50) values for rainbow trout and Daphnia magna. All simulated chlorothalonil applications produced runoff with concentrations that greatly exceeded the LC50 values for both indicator species. For some applications, concentrations of azoxystrobin, iprodione, and pentachloronitrobenzene exceeded LC50 values of at least one indicator species. Under the conditions simulated, runoff concentrations of metalaxyl, propiconazole, thiophanate methyl, and triadimefon were well below LC50 values of the indicator species. Although actual amounts of fungicide loaded into runoff were relatively low, these simulations suggest that turfgrass applications of fungicides with high intrinsic toxicity to indicator species could pose a risk to populations of primary and secondary consumers in aquatic ecosystems.

Evaluation of Composts for Suppression of Dollar Spot (Sclerotinia homoeocarpa) of Turfgrass

The use of composts in turfgrass disease management allows for a reduction in pesticide use in chemical control practices. Disease suppressive properties of composts rely on a number of factors including microbial activity, microbial population dynamics, nutrient concentrations, and other associated chemical and physical factors. Five composts were evaluated for suppression of dollar spot caused by Sclerotinia homoeocarpa. The dollar spot disease suppressive properties of selected compost formulations prepared in different years was evaluated. A third objective was to examine the effects of storage of compost (1 year) on the suppression of dollar spot. Field experiments were conducted in 1998 with compost prepared in 1997 to 1998. Applications of compost every 3 weeks throughout the season suppressed dollar spot of turf to levels not significantly different than applications of chlorothalonil fungicide applied at the manufacturer's lowest recommended preventative rate of 38.4 ml a.i./100 m2 every 2 weeks (P = 0.05). Single applications of composts at the start of the 1998 season were not effective in reducing disease. Field experiments in 1999 evaluated batches of two selected compost formulations, one batch produced in 1998 to 1999, another stored since production in 1997 to 1998. Composts were effective in suppressing disease to levels not significantly different than the fungicide controls, which showed up to 33% disease in 1998 and up to 31% disease in 1999 (P = 0.05). Storage of composts for up to 1 year did not affect their ability to reduce dollar spot severity (P = 0.05). The use of composts as plant disease suppressants is not likely to replace the use of commercial fungicides in dollar spot management. However, multiple applications of compost may reduce incidence and severity of dollar spot to levels at which chemical control may be reduced or eliminated for a significant portion of the season.

Composted Biosolids Incorporation Improves Turfgrass Establishment on Disturbed Urban Soil and Reduces Leaf Rust Severity

The effects of incorporation of compost to a disturbed urban soil on turfgrass establishment, growth, and rust severity were assessed in a replicated field study. A blend of two locally available composted biosolids (sewage sludge) was incorporated into a nutrient-deficient subsoil at a rate of 130 m3·ha-1, adding NO3-N, P, and K at 126, 546, and 182 kg·ha-1, respectively, to each compost-amended plot. Kentucky bluegrass (Poa pratensis L.), perennial ryegrass (Lolium perenne L.), and a mixture of these two species were seeded into both compost-amended and nonamended plots and observed for 1 year. Turfgrass establishment estimated from visual assessments of percentage cover and growth measured by clipping yields were significantly (P < 0.05) enhanced by the incorporation of the composted biosolids. These effects were first observed and most pronounced on plots seeded with perennial ryegrass and were apparent for the duration of the study. The severity of leaf rust caused by Puccinia sp. was significantly (P < 0.05) less on perennial ryegrass seeded on the compost-amended plots. This study demonstrates the feasibility and potential benefits of amending disturbed urban soils with composted biosolids to enhance turfgrass establishment and is the first report of the suppression of a foliar turfgrass disease through the incorporation of compost into soil.

Mycelial growth, sclerotial production and carbon utilization of three Typhula species

The mycelial growth, sclerotial production, and carbon utilization of the snow mould biocontrol agent Typhula phacorrhiza Fries were compared with the two grey snow mould fungi, Typhula ishikariensis Imai and Typhula incarnata Lasch ex Fries. Variation was observed among the four isolates for each species, but there was greater variation among species. All three species were able to grow at the lowest temperature (0°C), but temperature optima differed with T. ishikariensis lowest and T. phacorrhiza highest. On potato dextrose agar or potato malt agar at 10°C, T. phacorrhiza had greater radial growth than T. ishikariensis but less than T. incarnata. All species could utilize microcrystalline cellulose, bacto-cellulose, and glucose as carbon sources, but radial growth of T. phacorrhiza was significantly greater than T. incarnata and T. ishikariensis on these defined carbon sources tested, except for Indulin-AT, which was inhibitory to T. incarnata and T. phacorrhiza. This greater ability to utilize these structural and storage carbohydrates, combined with mycelial growth and sclerotial production over a wider range of temperatures, may help explain how some isolates of T. phacorrhiza are able to outcompete grey snow mould in field tests.Key words: turfgrass disease, biocontrol, psychrophilic.