Effect of Irrigation Timing on Dislodgeable Azoxystrobin Residues from Athletic Field Turf.

Azoxystrobin is a systemic broad-spectrum fungicide used extensively in turfgrass and was the world’s largest gross selling fungicide in 2012, with sales in excess of $1 billion USD. Research was completed to assess azoxystrobin dislodgeable foliar residues (DFR) and factors that affect it from treated turf vegetation. Previous research has shown post-application irrigation (PAI) can reduce pesticide DFR from turf vegetation; however, this management practice has not been evaluated to determine its effect on azoxystrobin dislodge. Field research was initiated April 27, 2015 in Raleigh, NC to measure dislodgeable azoxystrobin (0.56 kg ai ha^-1) foliar residues from perennial ryegrass (Lolium perenne L. ‘Carly’) following PAI (0.6 cm H₂0) at 0, 4, or 144 h after treatment (HAT). Sample collections occurred 1, 2, 3, 6, 12 or 24 d after treatment (DAT) at 7:00:00 (canopy moisture present) or 14:00:00 (canopy moisture absent) Eastern Standard Time.

From 1 to 3 DAT, irrigating 0 HAT reduced azoxystrobin DFR (3.6% to 6.8% of applied) more than 4 HAT (5.9% to 10.3%), which were both less than 144 HAT (9.9% to 15.5%). Azoxystrobin more readily dislodged at 1 DAT–7:00:00 (12.7% of applied) than 1 DAT–14:00:00 (9.0%); however, differences between sample collection timings within a day were not observed in subsequent sampling days. Lastly, irrigating 0 or 4 HAT resulted in detectable azoxystrobin DFR through 6 DAT, while delaying irrigation to 144 HAT extended detection to 12 DAT. In conclusion, irrigating azoxystrobin the day of application can reduce dislodgeable foliar residues, and should be implemented by turfgrass managers for soil-borne disease control to reduce potential human exposure.