Influence of Spray Application Technique on Spray Deposition in Greenhouse Ivy Pot Plants Grown on Hanging Shelves

As a result of the decreasing availability of authorized plant protection products, adequate pest control becomes more difficult in many ornamental crops and almost no information is available about the optimization of spray application techniques in ornamental crops. Yet, spray boom systems—instead of the still predominantly used spray guns—might improve crop protection management in greenhouses considerably. Application rate, nozzle type, and configuration will influence the spray deposition and, as such, its efficiency. In this study, spray deposition in ivy pot plants [Hedera algeriensis cv. Montgomery, Hibb.], grown on hanging shelves in greenhouses, was compared with a traditional spray gun with a disc-core nozzle and a manually pulled trolley equipped with two vertical spray booms. The sprayings with the spray gun were performed at an application rate of 8500 L ha. For the vertical spray boom system, two different reduced application rates (2500 and 5000 L ha) with five different combinations of nozzle type, size, and pressure for each application rate were investigated. This research underlined that, besides the application rate, also the spray application equipment used has an important effect on the spray depositions. Nozzle type, size, and pressure on the vertical spray boom system only had a minor effect on the spray deposition. Although the spray gun performed well on the easily accessible crop zone with the runners, its performance in the more dense main crop zone was inferior. With 240% more sprayed liquid (8500 L ha) and chemicals, the realized depositions in this crop zone were not significantly different from the ones obtained with the vertical spray boom system applying only 2500 L ha. Spraying at 5000 L ha, the vertical spray boom system achieved a 82.9% higher overall spray deposition in the main crop canopy zone compared with the spray gun at an application rate of 8500 L ha. For the sprays applied with the vertical spray boom system, doubling the application rate resulted in equally higher spray depositions, except for the inner canopy deposition for which higher application rates were more effective. Although ornamental plants occupy only 12% of the horticultural plant production (fruits, ornamentals, and vegetables) surface in Flanders (Belgium), their output (0.46 billion euro) represents not less than 34% of the total horticultural production value. Greenhouses take 4.3% of the horticultural production surface for their account; 33% (714 ha) of this surface is used to produce ornamental plants (Flemish Government, 2006). Goossens et al. (2004) showed that 90% of the growers still use high-pressure spray equipment (i.e., spray guns or lances) to apply plant protection products, although spray boom equipment is becoming increasingly popular. A survey carried out in 2007 among growers of ornamental plants confirms this and furthermore reveals that almost all growers are convinced that high application rates and spray pressures are indispensable to obtain a satisfactory coverage and sufficient penetration of the often dense crop canopies. This survey also revealed that the present-day spray application techniques are insufficient and need to be improved (Braekman and Sonck, 2008). Previous studies already demonstrated that the use of (vertical) spray booms improves spray distribution (Nuyttens et al., 2004a) and reduces labor costs and operator exposure (Nuyttens et al., 2004b, 2009a). For similar reasons, research into automatic spraying of plant protection products has been addressed by several authors like González et al. (2009), Moltó et al. (2000), and Subramanian et al. (2005). Despite these important advantages, many questions remain concerning the optimal settings for (automated) spray boom equipment (Braekman and Sonck, 2007). It is generally accepted that the foliar application of a pesticide to a crop is an inefficient process with only a fraction of the pesticide actually being retained on plants and some being lost to the ground (Balan et al., 2008; Salyani et al., 2007). This loss of pesticides to the ground is even more pronounced in the case of spraying potted plants grown on hanging shelves using a spray gun or lance. The amount retained on the crop depends on many factors, including the formulation of the pesticide (Gossen et al., 2008; Yu et al., 2009), the volume of spray applied (Gauvrit and Lamrani, 2008; Medina et al., 2005; Pergher and Gubiani, 1995), the type of spray equipment (Braekman et al., 2009; Ebert et al., 2004) and its operation (Halley et al., 2008), the weather conditions (Balan et al., 2008; Nuyttens et al., 2007a) and the droplet size spectrum (Abdelbagi and Adams, 1987; Nuyttens et al., 2007b, 2009b). Until now, very few studies have been carried out to improve the spray application techniques used in ornamental crops. A study of Gilles (1992) showed that an electrostatic reduced-volume application of permethrin insecticide to greenhouse-grown chrysanthemums resulted in significantly higher spray deposition compared with the conventional high-volume application. However, this technique also resulted in significantly higher contamination of nontarget surfaces of the greenhouse bench tops and aisle ways. Derksen et al. (2008) concluded that when spraying a poinsettia canopy with a single-nozzle handgun sprayer, the variability in deposition across the treatment area is a continuing problem. Based on two experiments, Zhu et al. (2008) demonstrated that an increase of the application rate when spraying nursery trees could greatly increase spray deposition but did not greatly increase spray coverage on Received for publication 5 Aug. 2009. Accepted for publication 8 Sept. 2009. We acknowledge the Flemish Government–IWT Vlaanderen for financial support. We also thank the ‘‘Research Center for Ornamental Plants (PCS),’’ the local grower, and the technicians for supplying equipment, greenhouses, and technical support. To whom reprint requests should be addressed; e-mail [email protected]. HORTSCIENCE VOL. 44(7) DECEMBER 2009 1921 PEST MANAGEMENT