Effects of Vegetated Waterways on the Pesticide Content of Runoff Water at a Container Nursery Jeanne A. Briggs and T. Whitwell Department of Horticulture, Clemson University M.B. Riley Department of Plant Pathology and Physiology, Clemson University

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Though current management practices in the production of containerized plant materials require the frequent use of pesticides to control weeds, insects and pathogens, information on the movement and environmental fate of the chemicals is limited. Granulated pesticide formulations are popular because of applicator safety and handling ease, and up to 80% of the pesticide may be deposited onto the production surface. Overhead irrigation, typically 30% efficient, generates runoff water which may transport the pesticide, and recycling of water presents the potential for the introduction of pollutants onto the growing beds. Our earlier research projects at container nurseries in South Carolina detected herbicides in the runoff water, and in the sediment and water of irrigation containment ponds.

Vegetative filter strips and waterways have been utilized extensively in the treatment of municipal waste waters and runoff waters from pulp mills, livestock feed lots and agricultural lands. Grasses and aquatic plants are efficacious removers of nutrients and sediments from runoff water. Grasses reduce the transport capacity and sediment movement of runoff waters by reducing flow and allowing time for infiltration of pollutants into soils. Grassed buffer strips contiguous to agricultural lands have reduced the pesticide concentration of runoff water, and grassed filter strips have been shown to reduce atrazine in the runoff.

The common cattail, Typha latifolia, is a frequent component of vegetative treatment systems due to its capacity to withstand adverse growing conditions, and to accumulate and tolerate heavy metals such as lead, zinc, nickel, copper, iron and manganese. Concentrations of lead and zinc were reduced 95 and 80% respectively by an aquatic treatment pond of which T. latifolia was

The objectives of this research were to investigate the movement of pesticides generated during container nursery production, and to determine if vegetated waterways of grass and cattails would reduce the pesticide content of runoff water.

Materials and Methods

Research was conducted at an operating container plant nursery in northwestern South Carolina Gilbert's Nursery, Chesnee, SC). One growing area, encompassing over 3 acres and isolated from the rest of the nursery, sloped uniformly and unidirectionally so that runoff water could easily be channeled and directed. A 300' long by 6' wide waterway of hybrid bermuda grass (Cynodon dactylon x C. transvaalensis) was planted to receive runoff from half of the site. The remaining growing area drained across a gravel and clay road bed (reference ditch). A 300' long planting of cattails (Typha latifolia ) was installed to further filter the runoff which drained through the grass waterway. Weirs were installed at the termination of all waterways to facilitate sampling and to allow for quantification of runoff volumes.

Commonly used pesticides, an insecticide, fungicide, and a formulation of two preemergent herbicides, were applied at recommended rates (Table 1), in two applications, six weeks apart, one year after establishment of the waterways.

A two hour irrigation event (0.37 inches/hour) followed the pesticide application and samples of runoff were collected from all waterways at the weirs at 10, 30, 50, 70, 90, 110, and 130 minutesafter runoff began. Sampling continued on 1, 2, 4, and 8 days after pesticide application. Our previous research had demonstrated that the pesticides did not persist beyond 8 days after treatment.

Results

Runoff volumes: Of applied irrigation volumes, 30% could not be accounted for as runoff water leaving site. 35% of the applied amounts were measured at both the grass and reference waterways. The cattail treatment further reduced the amount of runoff leaving the grass waterway by 5% (Figure 1).

Pesticide movement: All pesticides were detected on the day of application (DOA), though amounts of chlorpyrifos and trifluralin were very negligible and approached the limits of detection. Such results are expected due to the large Kow (low affinity for water) and volatile nature of both chemicals. Thiophanate-methyl was detected on the DOA in all waterways. Amounts varied from 17 to 42 g moving through the waterways into offsite water.

Isoxaben was detected through 8 days after application with amounts approaching the limit of detection. The highest amount detected was 86 g which left the reference ditch on the DOA.

Pesticide reduction: Isoxaben losses were reduced 21% by the grass waterway as compared to the reference ditch. The cattail treatment further reduced movement of the pesticide by 12%. Thiophanate-methyl losses were reduced 25% by the grassed waterway, and 60% by traversing the grass and cattail treatments as compared to the reference waterway (Figure 2).

Conclusion

Not all pesticides utilized in the production of container grown plant material have the potential to move in runoff waters. Isoxaben and thiophanate-methyl are potentially transported in runoff, and the amount of pesticide lost may be reduced by the use of vegetated waterways.

Last Updated 2/1/97