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 targets inside canopies. Literature describing research results on optimal spray application techniques for fruits and vegetables grown in greenhouses also offers interesting related information. Tanigawa et al. (1993) reported an inadequate deposit of fungicide on the lower leaf surface of several strawberry cultivars for control of powdery mildew when swinging a nozzle pendulously over the crop. Nuyttens et al. (2004a) demonstrated that reducing the vertical nozzle spacing from 0.50 to 0.35 m when spraying with vertical spray booms was a simple and cheap adaptation to obtain a much better spray distribution in tomatoes as well as in peppers. Bjugstad and Sønsteby (2004) underlined the importance of spray equipment when spraying an outdoor strawberry crop. Multiple 80° flat fan nozzles at a distance of 200 mm from the plant proved to be the best solution for practical use. For smaller and larger plants, three ISO 03 nozzles and five ISO 05 nozzles achieved the highest deposition and coverage, respectively. Braekman et al. (2009) found that a vertical spray boom performed better than the reference spray equipment in strawberries (spray gun) and in tomatoes (air-assisted sprayer) and that nozzle type and settings significantly affected spray deposition and crop penetration.
Besides the traditional fixed or rolling benches on the floor, Flemish growers of potted plants frequently use hanging shelves (Braekman and Sonck, 2008). Depending on the type of greenhouse structure, one or more of these shelves are positioned at 2 to 4 m height in the greenhouse arches. In this way, growers try to make maximal use of the available heated greenhouse space. In almost all cases, the shelves are used to store either plants at an early growth stage or mother stock plants. The actual height and width of the shelves varies from company to company or even within a company. Because these shelves are located above the traditional benches, closely situated to the roof infrastructure of the greenhouse, the only currently available and useful equipment to apply plant protection products to the plants stored on the shelves are spray guns. In most cases, the spray gun is operated from the ground floor and thus, the spray cloud has to be targeted from quite some distance and from below toward the crop canopies.
In Belgium, almost all plant protection products authorized for the treatment of greenhouse ornamental plants express the dose as a concentration (e.g., 50 g/100 L spray volume) (Fytoweb, 2008) that is different from the more commonly used dose rate/ha (Meynecke, 2004). It is up to the growers to decide themselves the actual volume rate and thus also the quantity of plant protection product applied on a certain surface. It is believed that growers base these decisions on crop properties (e.g., growth stage, plant and canopy density, leaf properties) and pest occurrence (e.g., intensity and site of infestation) to determine the optimal application rate to treat a specific crop. Unfortunately, in practice, the majority of the growers do not bother to do this exercise for each treatment and just spray until runoff. Because the definition of the starting point of runoff is a rather personal matter, very divergent quantities of spray liquid are used when a number of growers are individually asked to spray a given crop until runoff (Bjugstad and Hermansen, 2008). Moreover, information on labels usually provides little guidance on application techniques other than advising the operator to provide good coverage (Derksen et al., 2008). To simulate this situation, the presented experiment included three different application rates all with the same tracer concentrations.
The main objective of this research was to investigate the effect of spray application technique on the spray deposition in ivy pot plants grown on hanging shelves in greenhouses. In particular, the effect of application rate, nozzle type, size and spray pressure, and the difference between the traditional spray gun and a vertical spray boom system was investigated.
Abdelbagi, H.A. & Adams, A.J. 1987 Influence of droplet size, air-assistance, and electrostatic charge upon the distribution of ultra-low-volume sprays on tomatoes Crop Prot. 6 226 233
Balan, M.G., Abi-Saab, O.J.G., da Silva, C.G. & do Rio, A. 2008 Deposition of the spraying suspension for three spray nozzles under different meteorological conditions Semina-Ciencias Agrarias 29 293 298
Braekman, P., Foqué, D., Messens, W., Van Labeke, M.-C., Pieters, J.G. & Nuyttens, D. 2009 Effect of spray application technique on spray deposition in greenhouse strawberries and tomatoes Pest Mgt. Sci.
Braekman, P. & Sonck, B. 2007 An appropriate technical inspection methodology to tackle the great diversity of spray equipment used in Flemish greenhouses Asp. Appl. Biol. 83 95 98
Braekman, P. & Sonck, B. 2008 A review of the current spray application techniques in various ornamental plant productions in Flanders, Belgium Asp. Appl. Biol. 84 303 308
Butler Ellis, M.C. & Scotford, I.M. 2003 The deposit characteristics of pesticide sprays applied at low volumes Proc. BCPC Int.Congress Crop Sci. Technol. 279 284
Cross, J.V., Walklate, P.J., Murray, R.A. & Richardson, G.M. 2001a Spray deposits and losses in different sized apple trees from an axial fan orchard sprayer: 1. Effects of spray liquid flow rate Crop Prot. 20 13 30
Cross, J.V., Walklate, P.J., Murray, R.A. & Richardson, G.M. 2001b Spray deposits and losses in different sized apple trees from an axial fan orchard sprayer: 2. Effects of spray quality Crop Prot. 20 333 343
Cross, J.V., Walklate, P.J., Murray, R.A. & Richardson, G.M. 2003 Spray deposits and losses in different sized apple trees from an axial fan orchard sprayer: 3. Effects of air volumetric flow rate Crop Prot. 22 381 394
De Moor, A., Vergauwe, G. & Langenakens, J. 2002 Evaluation of chemical analysis of minerals for the assessment of spray deposits Asp. Appl. Biol. 66 409 420
Derksen, R.C., Frantz, J., Ranger, C.M., Locke, J.C., Zhu, H. & Krause, C.R. 2008 Comparing greenhouse handgun delivery to pointsettias by spray volume and quality Trans. ASABE 50 27 33
Ebert, T.A., Derksen, R.C., Downer, R.A. & Krause, C.R. 2004 Comparing greenhouse sprayers: The dose-transfer process Pest Manag. Sci. 60 507 513
Gauvrit, C. & Lamrani, T. 2008 Influence of application volume on the efficacy of clodinafop-propargyl and fenoxaprop-P-ethyl on oats Weed Res. 48 78 84
Gilles, D.K. 1992 Foliar and non-target deposition from conventional and reduced-volume pesticide application in greenhouses J. Agr. Food Chem. 40 2510 2516
González, R., Rodríguez, F., Sánchez-Hermosilla, J. & Donaire, J.G. 2009 Navigation techniques for mobile robots in greenhouses Appl. Eng. Agr. 25 153 165
Gossen, B.D., Peng, G., Wolf, T.M. & McDonald, M.R. 2008 Improving spray retention to enhance the efficacy of foliar-applied disease and pest-management products in field and crop rows Can. J. Plant Pathol. 30 505 516
Goossens, E., Windey, S. & Sonck, B. 2004 Information service and voluntary testing of spray guns and other types of sprayers in horticulture Asp. Appl. Biol. 71 41 48
Halley, S., Van Ee, G., Hofman, V., Panigrahi, S. & Gu, H. 2008 Fungicide deposition measurement by spray volume, drop size, and sprayer system in cereal grains Appl. Eng. Agric. 24 15 21
Jensen, P.K. & Nielsen, B.J. 2008 Influence of volume rate and nozzle angling on control of potato late blight with flat fan, pre-orifice and air induction nozzles Asp. Appl. Biol. 84 447 452
Langenakens, J., Vergauwe, G. & De Moor, A. 2002 Comparing hand-held spray guns and spray booms in lettuce crops in a greenhouse Asp. Appl. Biol. 66 123 128
Medina, R., Sánchez-Hermosilla, J., Agüera, F. & Gazquez, J.C. 2005 Deposition analysis of several application volumes of pesticides adapted to the growth of a greenhouse tomato crop Acta Hort. 691 179 185
Moltó, E., Martín, B. & Gutiérrez, A. 2000 Pesticide loss reduction by automatic adaptation of spraying on globular trees J. Agr. Eng. Res. 78 35 41
Meynecke, J.O. 2004 Evaluation and authorisation of plant protection products within the European Union J Appl. Bot. Food Qual. 78 157 160
Murray, R., Cross, J. & Ribout, S. 2000 The measurement of multiple spray deposits by sequential application of metal chelate tracer Ann. Appl. Biol. 137 245 255
Nuyttens, D., Braekman, P., Windey, S. & Sonck, B. 2009a Potential dermal pesticide exposure affected by greenhouse spray application technique Pest Manag. Sci. 65 781 790
Nuyttens, D., De Schampheleire, M., Verboven, P., Brusselman, E. & Dekeyser, D. 2009b Droplet size-velocity characteristics of agricultural sprays Trans. ASABE 52 1471 1480
Nuyttens, D., De Schampheleire, M., Baetens, K. & Sonck, B. 2007a The influence of operator controlled variables on spray drift from field crop sprayers Trans. ASABE 50 1129 1140
Nuyttens, D., Baetens, K., De Schampheleire, M. & Sonck, B. 2007b Effect of nozzle type, size and pressure on spray droplet characteristics Biosystems Eng. 97 333 345
Nuyttens, D., Windey, S. & Sonck, B. 2004a Optimisation of a vertical boom for greenhouse spray applications Biosystems Eng. 89 417 423
Nuyttens, D., Windey, S. & Sonck, B. 2004b Comparison of operator exposure for five different greenhouse spraying applications J. Agr. Saf. Health 10 187 195
Pergher, G. & Gubiani, R. 1995 The effect of spray application rate and airflow on foliar deposition in a hedgerow vineyard J. Agr. Eng. Res. 61 205 216
Piché, M., Panneton, B. & Thériault, R. 2000 Field evaluation of air-assisted boom spraying on broccoli and potato Trans. ASABE 43 793 799
Subramanian, V., Burks, T.F. & Singh, S. 2005 Autonomous greenhouse sprayer vehicle using machine vision and ladar for steering control Appl. Eng. Agr. 21 935 943
Tanigawa, M., Nakano, T., Hagihara, T., Okayanma, K. & Sezaki, S. 1993 Relationship between the control effect of fungicides on powdery mildew (Sphaerotheca humuli) and their deposits on strawberry (Fragaria ananassa) leaves J. Pestic. Sci. 18 135 140
Yu, Y., Zhu, H., Ozkan, H.E., Derksen, R.C. & Krause, C.R. 2009 Evaporation and deposition coverage area of droplets containing insecticides and spray additives on hydrophilic, hydrophobic, and crabapple leaf surfaces Trans. ASABE 52 39 49
Zhu, H., Zondag, R.H., Derksen, R.C., Reding, M. & Krause, C.R. 2008 Influence of spray volume on spray deposition and coverage within nursery trees J. Environ. Hort. 26 51 57