Targeted spray technology to reduce pesticide in runoff from dormant orchards

Abstract

A commercial target-sensing spray system was used to spray insecticide onto a dormant orchard in order to quantify the resulting reduction in insecticide in surface water runoff from the orchard. The field trials compared ground deposit and resulting runoff from target-sensing spraying versus conventional air-blast spraying. The test orchard had distinct gaps between trees and provided an environment where the target-sensing spray technology was expected to provide a significant benefit. Six replicated plots were created for each spray treatment method and artificial rainfall was applied using a sprinkler system to ensure a consistent and uniform simulated rainfall event for all treatment plots. The target-sensing sprayer produced a 40% reduction in the spray application rate and achieved a 41% reduction in ground deposition compared with the conventional air-blast sprayer. Pesticide concentration in surface water runoff was reduced by 44% with the target-sensing sprayer versus the conventional application. The results document the environmental and economic benefits provided by target-sensing spray technology in dormant orchards.

Introduction

Nut and fruit production in the Sacramento Valley of California in the United States uses dormant season application of pesticides and fertilizers to maintain in-season pest control and optimal crop yields. Diazinon (O,O-diethyl-O-[6-methyl-2-(1-methylethyl)-4-pyrimidinyl] ester) is an organophosphate pesticide that is applied to orchards and field crops during the dormant (winter) season to control a variety of insect pests. Diazinon was first registered for use in the United States in 1956 and numerous commercial products contain diazinon as the active ingredient. It was first developed as a non-systemic insecticide and nematicide for use against soil insects and pests of fruit trees in addition to vineyards, row crop vegetables, rice, sugarcane, forage, range, pasture, grasslands, tobacco, and horticultural crops (Agency for Toxic Substances and Disease Registry (ATSDR), 1996).

The majority of rainfall in the Sacramento Valley occurs during the winter, increasing the potential for diazinon and other pesticides to be washed from the treated areas and into rivers and tributaries during storm events (Kuivila and Foe, 1995; Werner et al., 2004). For example, recent studies by Brady et al. (2006) report that off-site movement of two pesticides (diazinon and esfenvalerate) is found in California Rivers and suggest that the increase in use of these pesticides due to the common belief on their hydrophobicity leading to a reduction in these materials found in surface water runoff flows may be misleading. Pesticides (e.g., diazinon) that originate from surface water runoff events and end up in rivers and tributaries can cause metabolic problems in the early life stages of Chinook salmon (Viant et al., 2006).

Farmers, local governments, agricultural coalitions, universities, and the chemical industry are cooperating to develop and evaluate various pesticide reduction or mitigation best management practices (BMPs). These BMPs include pest threshold monitoring, use of less toxic and organic pesticides, installation of vegetated riparian buffers and filter strips, use of cover crops in orchard floors, improved sprayer calibration, and reduced herbicide applications. Werner et al. (2004) report that diazinon is routinely detected in surface waters in California and these detections are typically coincident with dormant spray activities in orchards in the winter months. Their study considered several different ground cover crops for reducing pesticide transport in surface water runoff; results indicated that pesticide loading in surface water runoff could be reduced up to 50% by vegetative ground cover.

Beginning in 2003, the California Department of Pesticide Regulation began reviewing dormant spray regulations and has recently implemented new restrictions, which include a prohibition of ground or aerial applications of dormant insecticides within less than 48 h of a predicted rain event, prohibition of spraying within 30 m of any sensitive aquatic habitat, and establishing monitoring thresholds for the presence of pest populations at crop damaging levels. Additionally, Hapeman et al. (2003) report on the need to accurately describe processes that govern the transport, degradation, and bioavailability of pesticides under conditions reflecting actual agronomic practices and the need to identify vulnerable areas, temporal and spatial variations of pesticide use, and predicting how pesticides will behave in environmental matrices.

This study was motivated by previous work that established the benefits in target-sensing spraying for reducing pesticide application rates and non-target deposition. In operation, target-sensing sprayers use ultrasonic or optical sensors to continuously detect the presence or absence of target trees; in regions where a sparse target is detected, spray output is modulated; when no target is detected, spraying is ceased. In dormant orchards, especially in young or widely spaced trees, the open area between and underneath trees can be a significant proportion of the treated space. These situations offer the potential for significant benefits from target-sensing spraying (Giles et al., 1989). A series of field experiments (Giles and Downey, 2005) in dormant orchards over a number of seasons determined that use of target-sensing sprayers decreased pesticide application rates by 15–45%, depending on orchard configuration. Concomitant reductions in ground deposit were 5–71% and generally correlated with the reduction in application rates. Other researchers (e.g., Wenneker et al., 2003; Zaman et al., 2005; Solanelles et al., 2006) also reported on spray savings and reduced environmental effects from using target-sensing, ultrasonic sprayers. The underlying hypothesis in this study was that target-sensing spraying, by reducing the non-target spray deposit on the orchard floor and available for runoff, would subsequently reduce the level of pesticide leaving the orchard in runoff water.