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PM07 Pollutant Chemistry Transport, Cycling and Fate
(PM092) Herbicide Export in Surface Water Discharged from Indian River Citrus Production Areas.
Wilson, P1, Boman, B1, Ferguson-Foos, J2, 1 University of Florida/IFAS, Indian River Research and Education Center, Fort Pierce, FL, USA2 Florida Department of Agricultural and Consumer Services, Tallahassee, FL, USA
ABSTRACT- Pesticide losses from citrus groves are a concern within the St. Lucie Estuary (SLE) and Indian River Lagoon (IRL) drainage basins. Of special concern is the loss of herbicides that may negatively impact submerged aquatic plant populations downstream in the freshwater and estuarine receiving water bodies. Pre-emergent and emergent herbicides are usually applied underneath citrus trees to limit competition for nutrients and water, and to allow workers to harvest fruit more easily. Herbicide bandwidth refers to the area underneath the trees that is usually maintained weed-free. An inter-disciplinary project funded by USEPA R4 through FDACS was initiated at the UF/IFAS-IRREC to investigate the influence of limiting the herbicide bandwidth on discharge of two representative herbicides in surface runoff water. Three different herbicide bandwidths were evaluated, including 1.2, 2.1, and 3 m widths on either side of the tree trunk. The herbicides norflurazon and simazine were applied to replicate citrus row-furrow-row experimental units. Surface water runoff events were initiated by applying overhead irrigation. Water samples were collected at the water furrow pipe as the water drained throughout the runoff event. Water depth measurements through a weir allowed estimation of the total volume of water discharged from water furrows during each sampling interval. In order to simulate a worst case situation, samples were collected from the first two runoff events occurring after application of the herbicides. There was a strong positive correlation between herbicide band width and average mass of norflurazon and simazine lost during the runoff events. During the first runoff event, norflurazon losses were 4.4 to 5 times greater from the 2.1 and 3-m treatments as compared to the 1.2-m treatment. During the second runoff event, losses from the 2.1 and 3-m treatments were 5-7 times greater than losses from the 1.2-m herbicide bandwidth. Simazine losses from the 2.1 and 3-m herbicide bandwidth treatments were approximately 2.7 times greater than from the 1.2-m bandwidth during the first runoff event and 4-5 times greater during the second runoff event. Results indicate that export of herbicide residues from citrus production areas can be greatly reduced by minimizing the width of the herbicide bands underneath trees.
Key words: norflurazon, simazine, runoff, BMP
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