Effects of sprayers and nozzles on spray drift and terminal residues of imidacloprid on wheat
Introduction
Pesticide spray drift is a significant environmental problem caused by pesticide application. Reducing pesticide spray drift and improving application efficiency are amongst the most important aspects for plant protection currently. Wheat (Triticum aestivum L.) ranks the third leading crop in China after rice (Oryza sativa L.) and maize (Zea mays L.) and is cultivated throughout the country (Wang et al., 2009). Pesticide spray drift can be greatly reduced by improving the application technique. Spray drift may be influenced by various factors (Carlsen et al., 2006), as follows: (1) meteorological factors: wind speed, atmospheric stability, turbulence, temperature, and humidity; (2) application factors: sprayer type, nozzle type, orifice size, spraying pressure, spraying height, angle at which pesticides are spread, and driving speed; and (3) formulation: additives, density, surface tension and viscosity. The present study is mainly focused on the influence of sprayers and nozzles on spray drift.
Applicators should consider the nozzle types that provide adequate coverage and sufficient drift reduction properties. Different types of nozzles, such as flat fan, hollow cone, and spinning disc/cage (with/without air assistance), are used for broadcast spraying (Yarpuz-Bozdogan et al., 2011). Most field crop sprayers use flat-fan nozzles to apply a uniform coverage across the top of the target. Aiming to enhance efficacy and to minimize spray drift, some manufacturers have designed new nozzles with emphasis on improved droplet size control. Chamber and venturi style tips have been the most successful applications (Wolf, 2004). LECHLER nozzles, including LU multi-range universal flat-spray nozzles, AD anti-drift flat-spray nozzles, and IDK venturi air-induction nozzles, are the commonly used flat-fan nozzles that can effectively reduce spatial drift (Lechler Inc., 2012).
Several recent developments have been aimed at modifying existing equipment to increase deposition efficiency. Air-assist technology or some kind of shield or shroud is generally used to overcome the drift-producing air currents and turbulence that occur around the nozzle during spraying. Although air-assist technology has already been proved to be an effective way to increase deposition and to reduce spray drift, commercially available equipment has not yet been widely adopted because of its relatively high cost (Ozkan et al., 1997). A sprayer with a mechanical shield has a good capacity to reduce spray drift, and can be easily employed by farmers, especially in developing countries due to its low cost and simple structure. The guided-baffle shield sprayer (GBSS) changes the flow field around the nozzle, which could reduce the horizontal velocity and produce the down-vertical airflow. In this way, the drift potential of droplets can be reduced and the droplets are directed to be deposited on the target. Many studies (Cenkowski et al., 1994, Furness, 1991, Smith et al., 1982, Fehringer and Cavaletto, 1990, Maybank et al., 1990) have been conducted to investigate the effects of a mechanical shield on drift deposits. Fehringer and Cavaletto (1990) revealed that the use of shrouded hoods over boom sprayers could greatly reduce the spray drift under various conditions. Smith et al. (1982) conducted both laboratory and field tests to quantify the effects of a mechanical and a pneumatic shield on drift deposits. The laboratory test results indicated that a mechanical shield could reduce spray drift deposits by 70%.
High pesticide utilization efficiency will cause more pesticide deposition on the crop. Pesticide residues on crops pose a potential risk for human health. Pesticide application methods influence the amount of pesticide residue on fruits (Yarpuz-Bozdogan et al., 2011) and vegetables (Qin et al., 2010, Wei et al., 2009). However, there is limited information about the effects of different nozzle type combinations applied with GBSS on spray drift and on the terminal residues in the field crop, which is related to food safety.
Imidacloprid, which is one of the most widely used insecticides for controlling aphids for wheat, was applied as the target pesticide in this work (Nayak and Daglish, 2006). A field study was conducted to investigate the effects of three types of LECHLER nozzles (LU120-02, AD120-02, and IDK120-02) and two kinds of sprayers (conventional sprayer (CS) and GBSS, as shown in Fig. 1A and 1B, respectively) on spray drift. Sediment drift, airborne drift profile and pesticide residues on the harvested wheat were analyzed. This study can provide guidance on the proper and safe application of pesticides for developing countries.
Section snippets
Site and application
The trial was conducted on the 1 and 2 of June 2011 at Machikou Town, Beijing, China (geographical longitude 116.19° E, latitude 40.17° N). Each plot grown with wheat at grain-filling stage had a size of 40 m × 24 m. The crop height was 60 cm. The row spacing of the wheat was 20 cm. Spraying was conducted in the morning (8:30–10:00) and afternoon (15:00–17:00) using LECHLER nozzles (LU120-02/AD120-02/IDK120-02) mounted on a 6 m spraying boom. Two field sprayers (GBSS and CS) were employed. The
Analytical method validation
The external standard method was used for quantitative analysis. Drift amount recovery tests were conducted by fortifying a certain amount of standard solutions of imidacloprid into the sampling collectors (e.g., five brushes for airborne spray drift and six dishes for sediment drift), followed by the extraction procedure described in Section 2.5.1. The recoveries of airborne spray drift and sediment drift ranged from 72.5% to 78.5% and 96.8%–98.5% respectively with acceptable relative standard
Effects of nozzles and sprayers on spray drift
The study indicates that the spray drift (airborne spray profile and sediment drift) amount induced by the application method from high to low were LU120-02 > IDK120-02 > AD120-02. The amount of airborne spray profile decreased with the increase of height. Spray drift is caused by a number of equipment specific and meteorological factors, such as droplet size, sprayer velocity, spray height, wind velocity, relative temperature, and ambient humidity. The velocity of droplets exiting from a
Acknowledgements
For the assistance in the field study, the authors would like to thank all the members of the Chemicals Application Technology Group (College of Science, China Agricultural University) and the Pesticide Residue and Environmental Toxicology Group (College of Science, China Agricultural University). The authors are greatful to Antony Anderson from University of Waterloo for English modification. The authors also thank the anonymous reviewer for the valuable comments and suggestions on the paper.
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Huiyu Zhao and Chen Xie contributed equally to this work.