Abstract2,4-dimethylamine salt (2,4-D) is a synthetic auxin herbicide used extensively in turfgrass for selective broadleaf weed control. Previous research has shown that 2,4-D can dislodge from treated turf, notably in the presence of canopy moisture. Practitioners commonly apply 2,4-D in combination with various commercially available surfactants to increase efficacy. Field research was completed to evaluate the effect of surfactant inclusion and sample collection time within a day on dislodgeable 2,4-D residue from perennial ryegrass. Research was initiated May 24, 2016 in Raleigh, NC and repeated in time to quantify dislodgeable 2,4-D following application (2.1 kg ae ha–1) either alone or with a nonionic surfactant (0.5% vol/vol). Sample collection occurred 1, 2, 3, 6, 12 or 24 d after treatment (DAT) at AM [7:00 AM Eastern Standard Time (EST)] and PM (2:00 PM EST) sample timings within a day. 2,4-D applied with surfactant (0.4% to 25.4% of applied) reduced dislodgeable foliar residue compared to 2,4-D applied alone (0.5% to 31.2%) from 1 through 6 DAT, whereas dislodgeable 2,4-D was not detected at 12 and 24 DAT. Regardless of surfactant inclusion or absence, samples collected in the AM resulted in a 5- to 10-fold increase in dislodgeable 2,4-D compared to samples collected in the PM from 1 through 6 DAT, suggesting that 2,4-D dislodgeability may be influenced by conditions favoring canopy moisture development. This research will improve turfgrass management practices and research designed to minimize human 2,4-D exposure.

Plant canopies in established turfgrass systems can intercept an appreciable amount of sprayed pesticides, which can be transferred through various routes onto humans. For this reason, transferable pesticide residue experiments are required for registration and re-registration by the United States Environmental Protection Agency (USEPA). Although such experiments are required, limited specificity is required pertaining to experimental approach. Experimental approaches used to assess pesticide transfer to humans including hand wiping with cotton gloves, modified California roller (moving a roller of known mass over cotton cloth) and soccer ball roll (ball wrapped with sorbent strip) over three treated turfgrass species (creeping bentgrass, hybrid bermudagrass and tall fescue maintained at 0.4, 5 and 9 cm, respectively) are presented. The modified California roller is the most extensively utilized approach to date, and is best suited for use at low mowing heights due to its reproducibility and large sampling area. The soccer ball roll is a less aggressive transfer approach; however, it mimics a very common occurrence in the most popular international sport, and has many implications for nondietary pesticide exposure from hand-to-mouth contact. Additionally, this approach may be adjusted for other athletic activities with limited modification. Hand wiping is the best approach to transfer pesticides at higher mowing heights, as roller-based approaches can lay blades over; however, it is more subjective due to more variable sampling pressure. Utility of these methods across turfgrass species is presented, and additional considerations to conduct transferable pesticide residue research in turfgrass systems are discussed.

Azoxystrobin is a broad-spectrum strobilurin fungicide used widely in turfgrass systems, including lawns. Previous research has shown that various management practices influence pesticide dislodgement from turfgrass; however, limited research has been performed to determine their effect on azoxystrobin dislodge. A field experiment was conducted in Raleigh, NC, to quantify dislodgeable azoxystrobin (0.61 kg ai ha −1 ) foliar residue from tall fescue [Lolium arundinaceum (Schreb.) S.J. Darbyshire] across formulations (sprayable or granular), application timings (AM [0700 h Eastern Standard Time] or PM [1400 h Eastern Standard Time]), and postapplication irrigation timings (4 or 48 h after treatment [HAT]). Sample collection occurred 1, 2, 3, 4, 8, or 16 d after treatment (DAT). Evaluated management practices affected dislodgeable azoxystrobin, most notably from 1 to 4 DAT. Sprayable azoxystrobin applied in the PM resulted in greater azoxystrobin dislodged (1.0-8.0% of applied) compared with AM (0.3-5.5%), which were both greater than granular azoxystrobin applied in the AM or PM (<0.1-2.8%) from 1 to 4 DAT. Within sprayable azoxystrobin, five times greater azoxystrobin was dislodged by delaying postapplication irrigation until 48 HAT (1.2-11.8% of applied) compared with irrigation 4 HAT (0.2-1.2%) from 1 to 4 DAT. Information from this study improves our understanding of factors affecting pesticide dislodge and can be incorporated into turfgrass management strategies to minimize potential human pesticide exposure.

Indaziflam and oxadiazon are efficacious preemergence (PRE) herbicides used in warm season turfgrass due to their persistence and residual activity. It is beneficial to quantify effective concentrations for PRE control of summer annual weeds and determine whether these concentrations are maintained throughout weed emergence periods. Therefore, greenhouse bioassays were conducted with barnyardgrass, broadleaf signalgrass, doveweed, large crabgrass, and purple nutsedge. Treatments included indaziflam at 0, 4, 8, 12, 17, 21, 25, 29, 33, and 37 g ai ha−1 or oxadiazon at 0, 420, 841, 1,260, 1,681, 2,102, 2,354, 2,942, 3,363, and 3,783 g ha−1. Although PRE herbicides are not used to control perennial weeds, purple nutsedge was included to investigate the effect of selected herbicides on its growth. Herbicide EC50, EC80, and EC90 for seedling emergence inhibition and shoot and root mass reduction were quantified from log-logistic dose-response curves. Herbicide concentration that remains from a PRE application during the regional species-specific periodicity of emergence was predicted using first-order kinetics equations. Indaziflam and oxadiazon controlled seedling emergence 14 d after treatment (DAT) in the evaluated annual weeds and shoot and root mass in all species 84 DAT. Indaziflam applied in mid-March at 33 g ha−1 may provide up to 90% seedling emergence inhibition in large crabgrass and signalgrass; up to 80% in barnyardgrass; and up to 50% in doveweed. Oxadiazon applied in mid-March at 3,363 g ha−1 may provide up to 80% seedling emergence inhibition in all species. Indaziflam and oxadiazon may control up to 80% shoot mass and up to 50% root mass, respectively, in purple nutsedge and 80 to 90% shoot or root mass in other species. Such information is useful in evaluating adequacy of herbicide management practices for season-long weed control, and it aids turfgrass managers in applying PRE herbicides at optimal timing based on target weed species.

Azoxystrobin is a systemic broad-spectrum fungicide used extensively in turfgrass. Previous research has shown post-application irrigation can reduce dislodgeable pesticide residues from turf; however, this management practice has not been evaluated to determine its effect on dislodgeable azoxystrobin residue or if altering postapplication irrigation timing (PAIT) can influence dislodgeable azoxystrobin. Field research was completed to assess the effect of PAIT, sample collection timing within a day and over days on dislodgeable azoxystrobin residue from perennial ryegrass (Lolium perenne L.). Research was completed in Raleigh, NC, to quantify dislodgeable azoxystrobin (0.54 lb a.i. acre -1 ) from perennial ryegrass foliage prior to and following PAIT (0.25 inch H 2 O) immediate, 4, or 144 hours after treatment (HAT). Sample collections occurred 1, 2, 3, 6, 12 or 24 days after treatment (DAT) at 7:00 a.m. or 2:00 p.m. EST. From 1 to 6 DAT, treatments irrigated immediately reduced dislodgeable azoxystrobin foliar residue (<0.1-6.8% of applied) more than those irrigated 4 HAT (0.4-10.3%); which were both less than withholding irrigation 144 . Across PAIT more azoxystrobin was dislodged in the morning (1.0-12.7% of applied) compared to the afternoon (0.2-9.0%) from 1 through 6 DAT. This research will enhance turfgrass management practices intended to limit human pesticide exposure and provide information pertaining to azoxystrobin dissipation kinetics in turfgrass systems.

Plant canopies in established turfgrass systems can intercept an appreciable amount of sprayed pesticides, which can be transferred through various routes onto humans. For this reason, transferable pesticide residue experiments are required for registration and re-registration by the United States Environmental Protection Agency (USEPA). Although such experiments are required, limited specificity is required pertaining to experimental approach. Experimental approaches used to assess pesticide transfer to humans including hand wiping with cotton gloves, modified California roller (moving a roller of known mass over cotton cloth) and soccer ball roll (ball wrapped with sorbent strip) over three treated turfgrass species (creeping bentgrass, hybrid bermudagrass and tall fescue maintained at 0.4, 5 and 9 cm, respectively) are presented. The modified California roller is the most extensively utilized approach to date, and is best suited for use at low mowing heights due to its reproducibility and large sampling area. The soccer ball roll is a less aggressive transfer approach; however, it mimics a very common occurrence in the most popular international sport, and has many implications for nondietary pesticide exposure from hand-to-mouth contact. Additionally, this approach may be adjusted for other athletic activities with limited modification. Hand wiping is the best approach to transfer pesticides at higher mowing heights, as roller-based approaches can lay blades over; however, it is more subjective due to more variable sampling pressure. Utility of these methods across turfgrass species is presented, and additional considerations to conduct transferable pesticide residue research in turfgrass systems are discussed.

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