| Abstract/Contents: | "Regulatory issues of pesticides based on the downward movement of pesticides in fallow soil systems may not be appropriate for turf systems. If the fate of pesticides in turf were better understood, management plans that preserve their use in turf may be implemented. Previous studies have characterized the downward movement of some pesticides in conventional till systems; however, in turf, pesticides are rare ly applied to bare soil, and this knowledge is lacking. In turf, a lower fraction of pesticides reaches soil as a portion is intercepted by the turf canopy. In addition, some pesticides are adsorbed and metabolized by plants. Managed bermudagrass turf systems are likely stratified by pH, and the thatch layer may contain high levels of organic matter which can influence some pesticides' movement. Thatch layers also may contain diverse microbial populations which degrade pesticides and benefit from the regular applications of nutrients and irrigation to managed bermudagrass. Thus, the objective was to compare the downward movement of pesticides in a turf system to movement in a fallow system in times of rapid growth and dormancy. At the Sandhills Research Station near Pinehurst, NC, 581 m2 of 'Tifway' bermudagrass was sprayed with glyphosate, removed with a sod cutter, tilled, and fumigated with methyl bromide in May 2001. In a split-plot design, two replications of lysimeters 15 cm in diameter and 91 cm long were driven in June and August 2001 into fallow soil and established 'Tifway' bermudagrass mowed at 1.9 cm. Imazaquin, prodiamine, pronamide, and simazine were applied during times of rapid growth and dormancy at 0.56, 0.56, 1.7, and 2.2 kg ai/ha, respectively, in July and November 2001 to unique lysimeters in 2.3 m2 plots. The treatments were watered in with 1 cm of water after application. An infiltration study indicated that movement of water into bermudagrass was about half the rate as for fallow soil. In November 2001 and April 2002 120 days after application, the lysimeters were removed and divided into the following depths: 0-2, 2-4, 4-8, 8-15, 15-30, 30-45, 45-60, 60-91 cm. The soil was dried and sieved. The residues were extracted analyzed by gas chromatography. The reported concentrations are the means of two replications determined using zero for nondetects. In summer, prodiamine was detected in fallow soil at 285, 23, and 16 parts per billion (ppb) in the 0-2, 2-4, and 4-8 cm depths, respectively and 451 and 64 ppb in the 0-2 and 2-4 cm depths, respectively, in turf. In summer, pronamide was detected in fallow soil at 96 and 20 ppb in the 0-2 and 2-4 cm depths, respectively and 116 and 135 ppb in the 0-2 and 2-4 cm depths, respectively, in turf. Perhaps greater concentrations were detected in bermudagrass because the rate of microbial degradation was greater for these pesticides in the fallow soil system which may have less free carbon available but similar fertility. In summer, imazaquin was detected at 83, 24, and 19 ppb in the 0-2, 2-4, and 4-8 cm depth, respectively, in fallow soil and was not detected in any turf samples. Simazine was detected in fallow soil at 23, 96, 11, and 3 ppb in the 0-2, 2-4, 4-8, and 8-15 cm depths, respectively and only 33 ppb in the 0-2 cm depth in turf in summer. However, in winter during dormancy, simazine was detected in fallow soil at 110, 110, 100, 90, and 23 ppb in the 0-2, 2-4, 4-8, 8-15, 15-30 cm depths, respectively and was detected in turf at 1200, 350, 100, and 32 ppb in the 0-2, 2-4, 4-8, and 8-15 cm depths, respectively. In winter, bermudagrass is dormant and not absorbing and metabolizing pesticides. Residues for the remaining pesticides applied in winter have not been analyzed. Although more downward movement and greater concentrations of simazine were reported in winter, there was never greater downward movement in bermudagrass in summer or winter, and the degree of movement should not be problematic because the greatest depth reporting residues was 15 cm. Thus, the bermudagrass system may inhibit the downward movement of some pesticides applied in times of rapid growth. However, in time of dormancy, the bermudagrass system may not inhibit the downward movement of some pesticides." |
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