Pesticide Application Rates Research Articles

Monitoring Ground Water for Pesticides at a Golf Course ‐ A Case Study on Cape Cod, Massachusetts

AbstractThe town of Yarmouth, Massachusetts, proposed to locate a new municipal golf course within a delineated area of recharge to public water‐supply wells. Two concerns of town officials were (1) hydrologic impacts upon downgradient wells; and (2) water‐quality impacts from fertilizers and pesticides. In response to these concerns, a thorough hydrogeologic investigation was made, fertilizer and pesticide management programs were recommended, and a ground water monitoring program was developed.The golf course parcel was determined to be underlain by a sand and gravel aquifer composed primarily of glacial outwash. Water‐table maps confirmed that ground water flow was in the direction of several public water‐supply wells. A three‐dimensional finite‐difference flow model was used to determine the optimum location and pumping rates for irrigation wells. Potential nitrate‐nitrogen concentrations in the ground water were predicted to range from 5.0 to 7.9 milligrams per liter so slow‐release fertilizers were recommended.With the assistance of the EPA Office of Pesticide Programs, the list of proposed pesticides was reviewed and sorted into three categories based on the known leachability, mobility, and toxicity characteristics of each compound. Specific recommendations were made as to pesticide selection and application rate using that classification.A monitoring program was developed to provide an on‐going assessment of any effects on water quality related to the application of fertilizer or pesticide. The elements of the monitoring program include (1) specifications for monitoring wells and lysimeters, (2) a schedule for sampling and analysis, (3) specific concentrations of nitrates or pesticide compounds that require resampling and analysis, restriction of usage, or remedial action, and (4) regular reports to the Yarmouth Water Quality Advisory Committee and to the Yarmouth Water Department. In an effort to ensure the implementation of this program, a table of responsibilities was prepared, and a Memorandum of Understanding adopting the program was signed by the town agencies interested in water‐supply protection and the golf course operation.The monitoring facilities were installed with minimal problems as part of the golf course construction tasks. However, implementation of the sampling and analysis part of the program was accomplished only after some difficulty and delay. The assistance of the State Pesticide Bureau, the University of Massachusetts Department of Entymology, and the Massachusetts Pesticide Laboratory was enlisted when budgetary problems threatened to prevent implementation. It is apparent from Yarmouth's experience that the mere preparation of a plan is not sufficient by itself. Consultants who prepare the plan should make every possible effort to include implementation in their scope of services.

Use of lysimeters to estimate leaching of pesticides in agricultural soils

In this review of lysimeters, different aspects concerning soil-filling technique, lysimeter size and materials, and drainage-system type are discussed. The placement of lysimeters in the field is dealt with, as are other types of field measurements that can provide complementary information. Evaluations of various properties are based on the assumption that the lysimeters are to be used for estimating pesticide leaching. Guidelines for use in designing a suitable lysimeter experiment for this purpose are described, with special emphasis placed on using the results as a basis for pesticide registration. In this context, some general recommendations are identified. Concerning the lysimeter itself, stress is placed on the importance of using undisturbed soil monoliths. It is recommended that two soil types, i.e. sand and clay, be used and that the management practices carried out closely resemble normal farming practices. Further recommendations include weekly water sampling, two watering regimes, and use of the normal and double the normal application rate of pesticides.

Uncertainty and the Economic Threshold

Economic threshold, also called optimizing threshold, has been defined by economists to be the level of pest infestation that warrants an application of pesticide when the pesticide application rate is computed to maximize the grower’s profit. As often used in practice, however, economic threshold is assumed to be the level of pest infestation at which cost of the pest application (when the application rate is a fixed, predetermined value) equals cost of the damage prevented by the application. This is sometimes called the discrete-choice threshold. In either case, computations are ordinarily done assuming that all parameters of the problem are known with certainty. In reality, this assumption is often not correct; there is a great deal of uncertainty. Effect of uncertainty on the economic threshold computation was explored. Uncertainty may have a profound effect as illustrated by consideration of a simple model. Extension of this method to more complex, realistic models is described.

A Variable-Rate Pesticide Spraying System

ABSTRACT A variable-flow-rate pesticide application system using six bypass centrifugal pressure nozzles was designed, built, and tested. The rate of output flow from the nozzles was regulated by a single valve. The variation in nozzle flow rate and distribution characteristics with changes in bypass and inlet pressures were studied. A nozzle output flow turndown ratio of 6 to 1 was obtained. The spray angle varied from 86 to 80 deg over the 6 to 1 turndown ratio, affecting the combined-nozzle spray distribution patterns only slightly. The system provides the capability of adjusting the pesticide application rate or of maintaining a constant rate over a range of travel speeds by means of a single control valve without signifi-cant degradation of spray characteristics.

Maximum Pesticide Concentrations in Agricultural Runoff: A Semiempirical Prediction Formula

AbstractUsing data compiled from the literature on the concentrations of pesticides observed in runoff water, a semiempirical prediction formula has been constructed which is very crude, but which should be useful to water‐quality planners for estimating worst‐case pesticide inputs from agricultural sources. The maximum “edge‐of‐field” pesticide concentrations in individual runoff events can be predicted within about one order of magnitude if the pesticide formulation, use, and application rate are known, together with the time elapsed between application of the pesticide and subsequent runoff events. Pesticides are grouped into four broad classes according to their “availability” for runoff loss.

An investigation of the safety of cotton reentry after organophosphate application.

Twelve cotton insect scouts were monitored during an entire pesticide application season by weekly determinations of para-nitrophenol excretion and biweekly cholinesterase measurements. These data were compared to weekly reentry intervals and pesticide application rates to study the validity of a 48-hr minimum reentry interval for methyl parathion-treated cotton. Methyl parathion represented 54.2% of the total amount of pesticide used with toxaphene 35.3%, ethyl parathion 4.1%, and other 6.4%. A significant decrease in erythrocyte and plasma cholinesterase was observed during initial exposure but during peak exposure the cholinesterase levels had returned to normal. The maximum mean amount of methyl and ethyl parathion absorbed by calculation from PNP excretion was 0.95 mg/24hr (n = 12). Twelve percent of all reentries were within two days and during one week 48% occurred during the first two days after pesticide application.