Center Update: Fungicide Efficacy and Fate

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Effect of Management Practices On Fungicide Efficacy and Fate In Turfgrass Systems

PI: Travis Gannon; Student: Daniel Freund

INTRODUCTION

On bentgrass putting greens, pathogens responsible for many root and crown diseases reside in the thatch layer and throughout the rootzone (Kerns et al., 2008). Due to the high-density turf canopy, thatch regions, and organic matter found in rootzones, fungicide movement is limited (Garner et al., 2001) which may compromise fungicide efficacy. Two experiments (lab and field) were conducted to investigate if soil surfactant inclusion and irrigation practices influence fungicide distribution. In -previous CENTERE funded research, Jeffries et al. (2016) reported 20% of the applied azoxystrobin was removed in clipping collected the day of application from tall fescue. These experiments investigate mowing practices following an azoxystrobin application and its influence on persistence and efficacy.

METHODS

Objective 1:  Mefenoxam (Subdue MAXX®) delivery to the target site as affected by soil surfactant. Laboratory research was conducted in Raleigh, NC (NC State University Pesticide and Trace Element Lab) to evaluate the effect of soil surfactant inclusion on 14C-mefenoxam distribution in soil. Soil columns (20.6 cm length by 5.7 cm diameter) were packed with USGA specification putting green rootzone mix (90:10 sand:peat moss v:v). to a bulk density of 1.38 g cm-3. 24 hours before 14C-mefenoxam treatment, soil surfactant (Cascade PlusTM) was applied (19.1 L ha-1) to unique columns followed by 0.6 cm irrigation. 24 hours later, 14C-mefenoxam was applied (763 g a.i. ha-1) to the soil surface. Immediately following treatment, 0.6 cm irrigation was applied to all columns. Soil sample collection occurred on 0, 3, 7, 14, and 21 days after treatment (DAT). Soil columns were split length-wise and soil was collected in 2.5cm depths.

Objective 2: Field research was conducted at Lake Wheeler Turfgrass Field Laboratory to quantify the effect of post-application irrigation timing and amount on cyazofamid soil distribution. At initiation, cyazofamid (Segway®) was applied to unique plots at the current single application maximum rate (1.1 kg ai ha-1) on a USGA-spec putting green comprised of ‘A1/A4’ creeping bentgrass (Agrostis stolonifera L.) Following cyazofamid application, plots received either 0.3, 0.6 cm H2O irrigation either immediately, or after a 6-hour drying period, or no irrigation at all. At 0, 1, 2, 3, 5, 7 and 10 DAT, turfgrass clippings were collected via walk-behind reel mower to quantify residue loss via clipping collection. Additionally, at 0, 1, 5 and 7 DAT, core sample collections (10.8 cm diam; 92 cm2) were taken including 4 segments: remaining aboveground vegetation, as well as 0 to 2.5 cm, 2.5 to 5 cm and 5 to 7.5 cm soil depths.

Objectives 3 & 4: Two experiments were conducted in Raleigh NC (Lake Wheeler Turfgrass Field Laboratory) to investigate the effect of mowing timing and clipping collection practices, respectively, on azoxystrobin distribution persistence and efficacy. At initiation, azoxystrobin (Heritage TL®) was spray-applied in both experiments to unique plots at the current single application maximum rate (0.61 kg ai ha-1). In the first experiment, at 3, 10 and 17 days after treatment turfgrass plots were mown, and their respective clippings were either returned to their mown canopies, or removed entirely from the area, using a bag equipped to the mower. In the second experiment, plots were mown (9.5-cm) at 0, 1, 2, 3, 7 or 14 DAT and visually rated weekly for brown patch through 56 DAT. Plots were mown every 7 days following the first 7 DAT and regardless of mowing timing, clippings were returned to their respective canopies. In both experiments, turfgrass core samples (10.8 cm diam; 92 cm2) were collected for residue analysis at 3, 7, 14, and 21 DAT.

RESULTS/DISCUSSION

Objective 1:  In table 1, regardless if a soil surfactant was included, the majority of mefenoxam was detected at 0 to 2.5 cm depth (92% of applied), with less detected in 2.5 to 5.0 cm depth (3-6%). 14C-mefenoxam was not detected below 5.0 cm over the duration of the study. Pooled over sampling dates, there was no difference of mefenoxam recovered at 0 to 2.5 cm, regardless of surfactant use. In the 2.5 to 5.0 cm depth, the use of surfactant enhanced mefenoxam distribution with 5.8% of applied compared to 2.9% when mefenoxam was applied alone. Run 2 is currently underway.

Objective 2: Recovery in the remaining aboveground vegetation comprised the majority of the applied cyazofamid, with less located in the 0-2.5 cm and respective soil depths. In table 2, at sampling time 0 DAT, residue detection in the 0-2.5 cm layer for 0 hour (immediate) irrigation was 36.0% while detection in the same layer for 6 hour irrigation was 5.3%. Data suggest that irrigation immediately after cyazofamid application is necessary for residue movement past the thatch and throughout the soil matrix. Data suggest that delaying irrigation 6 hours allows cyazofamid to dry and sorb in the thatch.

Objective 3: In table 3, azoxystrobin residue quantification for vegetation and soil matrices demonstrated delaying mowing after a fungicide application increases the amount of residue recovered in the system. At 14 DAT, less was detected 0 DAT (immediate mowing) (21%) compared to mowing 14 DAT (52%).

Objective 4: Although non-significant, for each sampling date, returning turf clippings to the canopy after a mowing event resulted in greater azoxystrobin residue recovery in the shoots (13%) and soil (5%). When clippings were removed from the system, azoxystrobin recovery in the shoots (7%) and soil (3%) was less.

References

Kerns, J. P., and Tredway, L. P. 2008. Pathogenicity of Pythium species associated with Pythium root dysfunction of creeping bentgrass and their impact on root growth and survival. Plant Dis. 92:862-869.

Gardner, D.S. and Branham, B.E. 2001. Effect of Turfgrass Cover and Irrigation on Soil Mobility and  Dissipation of Mefenoxam and Propiconazole. J. Environ. Qual. 30:1612-1618.

Jeffries, M D. Off-Target Pesticide Displacement and Fate in Turfgrass, Riparian and Aquatic Systems. NC State University. Dissertation 2017.