Pesticide Downward Movement in a Bermudagrass System Compared with Movement in a Fallow System

NC StateUniversity Pesticide Downward Movement in a Bermudagrass System Compared with Movement in a Fallow System H.D. Cummings*, J.B. Weber, R.B. Leidy, F.H. Yelverton, and R.L. Brandenburg NCSU, Raleigh, NC

Introduction • Previous studies have characterized the downward movement of pesticides in conventional till systems. • If regulatory issues of pesticides are based on downward movement of pesticides in traditional agricultural systems, they may not be appropriate for turf systems.

Introduction • In turf, pesticides are rarely applied to bare soil. • In turf, a lower fraction of pesticides reaches soil. • In turf, some pesticides are absorbed and metabolized by plants (biological degradation). • Compared to agriculture, knowledge is generally lacking on pesticide fate in actively growing and dormant turf.

Introduction • Managed bermudagrass systems are stratified by pH. • Thatch layers have high levels of organic matter. • Organic matter and pH can influence some movement of pesticides. • Thatch layers contain diverse microorganism populations. • Nutrients and irrigation are applied at regular intervals to turf.

Objective • To compare the downward movement of pesticides in a bermudagrass system to movement in a fallow system.

Materials and Methods • ‘Tifway’ hybrid bermudagrass maintained at 1.9 cm at the Sandhills Research Station near Pinehurst, NC • Native soil (Candor sand) (sandy siliceous, thermic, Arenic Paleudult) (83% sand, 11% silt, 4% clay, 2% OM) (High potential for leaching)

Materials and Methods (continued) • In early May 2001, half of the bermudagrass area (580 m2) was sprayed with glyphosate; two weeks later, it was removed with a sod cutter.

Materials and Methods (continued) • The area was tilled once. • On May 25, 2001, the tilled ground was fumigated setting up a split plot design (Turf Vs Fallow Ground).

Materials and Methods (continued) • In June and August of 2001 and May 2002, a total of 40 soil column lysimeters (91 cm long x 15 cm in diameter) were installed in both turf and fallow soil.

Materials and Methods (continued) Plot size: 2.3 m2 470 L/ha Insecticide applied with shaker can Irrigated with 1 cm of water Six weeks after initial fumigation • Four herbicides • One insecticide • Two replications • Applied in July when turf was actively growing and in November when turf was dormant in 2001 and 2002

Treatments

Pesticide Classification

Materials and Methods (Continued) • After 140 days, the soil column lysimeters were harvested. • The soil in the lysimeters was divided into 8 depth increments. • Turf tissue was collected by depth. (Deeper increments may not have been analyzed) (Turf tissue data not presented )

Materials and Methods (Continued)

Materials and Methods (Continued) Sonication removes adsorbed compounds from soil (10 g soil). Rotoevaporator concentrates extract.

Materials and Methods (Continued) Gas chromatograph (GC) separates the compounds and determines the concentration of the compound of interest (TSD detector).

Thatch Layer Soil Organic Matter Profile of Turf and Fallow Soil 525 oC for 16 hours

Soil pH Profile of Bermudagrass and Fallow Systems More binding of cations to OM at high pH; however, simazine and imazaquin are more mobile at high pH

Simazine in Soil of Fallow and Turf Systems after 140 Days of Summer ND ND ND ND ND ND ND ND ND ND ND

Simazine in Soil of Fallow and Turf Systems after 140 Days of Winter * ND ND ND ND NA * Turf year 1 different from Fallow year 1 at depth 0-2 cm (p<0.05). ** Winter 1 concentrations greater than summer 1 (p<0.05)

Imazaquin in Soil of Fallow and Turf Systems after 140 Days of Summer ND ND ND ND ND ND ND ND ND ND ND ND

Imazaquin in Soil of Fallow and Turf Systems after 140 Days of Winter ND ND ND ND ND ND ND ND ND ND ND ND ND

Pronamide in Soil of Fallow and Turf Systems after 140 Days of Summer ND ND ND ND ND ND ND ND ND ND ND ND

Pronamide in Soil of Fallow and Turf Systems after 140 Days of Winter * * * ND ND ND ND ND ND ND ND ND ND * Fallow year 2 different from Turf year 2.

Prodiamine in Soil of Fallow and Turf Systems after 140 Days of Summer ND ND ND ND ND

Prodiamine in Soil of Fallow and Turf Systems after 140 Days of Winter ND ND ND ND

Fipronil in Soil of Fallow and Turf Systems after 140 Days of Summer ND ND ND ND ND ND ND

Fipronil in Soil of Fallow and Turf Systems after 140 Days of Winter ND ND ND ND ND ND ND ND

Conclusion • Initial concentrations (2 days) were greater in winter except for fipronil in the turf system. • More movement and higher concentrations tended to occur in winter (140 days) except for fipronil in bermudagrass and imazaquin in fallow systems. • Simazine and imazaquin were detected at greater concentrations in bermudagrass system (0-4 cm) than the fallow system in winter.

Conclusion (continued) • Simazine and imazaquin were detected at deeper depths and at greater concentrations in the fallow system than bermudagrass system in summer. • Pronamide was detected at greater concentrations in the bermudagrass system (0-4 cm) than in the fallow system in summer; however, pronamide was detected at deeper depths and at greater concentrations in the fallow system in winter. • Prodiamine movement was not influenced by actively growing or dormant turf.

Conclusion (continued) • Fipronil was detected at greater concentrations in summer in the bermudagrass system (0-4 cm) than the fallow system; however, more fipronil movement occurred in the fallow system in winter.

Summary • Generally, more downward movement and greater concentrations occurred in winter. • In bermudagrass, pesticides tended to stay in the thatch layer (0 – 4 cm). • In fallow soil, pesticides tended distribute more uniformly. • To reduce the potential for leaching, apply pesticides to actively growing bermudagrass.

Final Conclusions • Generally, more downward movement and greater pesticide concentrations occurred in winter. • In bermudagrass, pesticides tended to stay in the thatch layer (0 – 4 cm). • In fallow soil, pesticides tended distribute more uniformly.

Final Conclusions • Simazine is less likely to move to groundwater when applied to actively growing bermudagrass. • Fipronil can provide season-long control (120 day) by causing mortality or avoidance behavior.

Tarleton State University

Pesticide Downward Movement in a Bermudagrass System Compared with Movement in a Fallow System