Curative Evaluation of Biological Control Agents and Synthetic Fungicides for Clarireedia jacksonii

Abstract

Clarireedia jacksonii sp. nov. formerly Sclerotinia homoeocarpa F.T. Bennett, one of the causal agents of dollar spot, is the most widespread pathogen in turfgrass systems. Dollar spot (DS) affects both cool- and warm-season grasses, during a wide range of environmental conditions. Field studies were conducted at Clemson University, Clemson, SC, on a creeping bentgrass [Agrostis stolonifera L. var. palustris (Huds) cv. Crenshaw] putting green for 2 consecutive years from August to October in year 1 and July to September in year 2. The objective of the studies was to evaluate biological control agents (BCAs) and synthetic fungicides at reduced rates for their efficacy controlling dollar spot. Four replications of 1.5 × 1.5-m plots were used in the experimental design. Treatments included the following: Bacillus subtilis (BS); plant extract oils (EO) including clove oil + wintergreen oil + thyme oil; extract of Reynoutria sachalinensis (RS); Bacillus licheniformis (BL); chlorothalonil (CL); and azoxystrobin + propiconazole (AzP). Synthetic fungicides were used at reduced rates in combination with biological control agents, to evaluate curative control efficacy of various combinations. All reduced synthetic programs, except CL + EO, provided acceptable disease severity (≤15%) at the end of year 1 and acceptable (≥7) turfgrass visual quality. Azoxystrobin + propiconazole, CL, AzP + BL, AzP + EO, AzP + BS all provided ≤15% disease severity and ≥7 visual turfgrass quality 14 days after the last application in year 2.

Sensitivity of Clarireedia spp. to benzimidazoles and dimethyl inhibitors fungicides and efficacy of biofungicides on dollar spot of warm season turfgrass

“…Further, the lowest label rate of synthetic fungicide propiconazole (1/4) was sufficient to entirely suppress C. monteithiana growth when mixed with B. subtilis QST713 (3/4). Similar to our findings, Marvin et al (2020b) observed that ¼ label rate of B. subtilis QST713 exhibited the highest suppression in mycelial growth (>80%) over the ½ and full-strength treatments by establishing a containment zone around the inoculation plug that comprised short and stubby mycelium. Furthermore, in both the growth chamber and field experiments, we consistently observed the lowest disease severity and AUDPC with two different spray programs: a tank mix of 75% B. subtilis QST713 + 25% propiconazole applied every 28 days (T5) and 100% B. subtilis QST713 applied in rotation with a tank mix of 75% B. subtilis QST713 + 25% propiconazole every 14 days (T7).…”

“…An economic analysis of the spray programs tested in this study would identify the most feasible and cost-effective programs. In a similar study by Marvin et al (2020b), rotation applications of either pyraclostrobin or chlorothalonil (Daconil Ultrex ™ ) with BCA at reduced label rates every 30 days suppressed dollar spot severity below 10% on a creeping bentgrass putting green at South Area under the disease progress curve (AUDPC) of dollar spot resulting from the application of seven different spray programs (T1-T7) in the field experiments across both summer and fall seasons. Mean AUDPC with the same letters in the box plot are not significantly different according to Tukey's test (P<0.05).T1: nontreated control; T2: B. subtilis QST713 applied every 7 days; T3: B. subtilis QST713 applied every 14 days; T4: propiconazole applied every 28 days; T5: tank mix of 75% B. subtilis QST713 + 25% propiconazole applied every 28 days; T6: 75% B. subtilis QST713 + 25% propiconazole tank mix in rotation with 100% B. subtilis QST713 applied every 14 days; and T7: 100% B. subtilis QST713 in rotation with 75% B. subtilis QST713 + 25% propiconazole tank mix applied every 14 days.…”

Detection, characterization, and management of plant pathogens

“…Successful integration of biological fungicides into dollar spot management programs needs additional research to validate the efficacy of the products, especially at different levels of disease pressure. Nevertheless, the consensus of our findings with several previous studies holding promising results for BCAs will provide an impetus for effective dollar spot management to the turf industry (Latin, 2008;Marvin et al, 2020a;Koch et al, 2021b, Tomaso-Peterson, 2006.…”

“…Clarke et al (2020) (Nelson and Craft, 1991) and Pseudomonas aureofaciens Tx-1 on creeping bentgrass in Michigan (Powell et al, 2000). Marvin et al (2020a) evaluated the curative control efficacy of four BCAs (B. licheniformis SB3086, B. subtilis QST713, R. sachalinensis extr., and plant extract oils) along with two synthetic fungicides (chlorothalonil and azoxystrobin + propiconazole) in a different tank-mix combination and reported that all BCAs except R. sachalinensis extr. provided acceptable disease control (disease severity ≤15%) and turfgrass quality (≥7) against C. jacksonii in South Carolina on creeping bentgrass putting greens.…”

Development of a Co-Dominant Cleaved Amplified Polymorphic Sequences Assay for the Rapid Detection and Differentiation of Two Pathogenic Clarireedia spp. Associated with Dollar Spot in Turfgrass

“…These genetic factors for fungicide resistance differences have not yet been studied since the reclassification of the dollar spot causing pathogens. Of the studies that have published since the reclassification, some focus on one species, mainly C. jacksonii, while the others simply refer to older nomenclature or the genus [24,28,29].…”