# Special Issue on Pesticide Applications in Agricultural Systems
## 2 Main Aspects Involved in Pesticide Application in Agriculture  
Effective and efficient application of PPP in agriculture is a very complex task involving a lot of aspects ranging from active substance properties (physical status, volatility, selectivity, persistency) to climatic conditions (wind speed, air temperature, and relative humidity), from target structure (canopy or ground, vegetative development, canopy arrangement) to equipment features (state of maintenance, air assistance, proper calibration), and from operator awareness (level of education, training, expertise in choosing the appropriate operating parameters) to the reference legislative framework (ISO standards, European Directives, national and local obligations). All these aspects, and many others, have been studied by the scientific community and are well referenced in the literature, and some of them have been treated by the authors that contributed to this Special Issue (SI) on Pesticide Applications in Agricultural Systems. When spraying liquid PPP, a key factor that affects most aspects of a phytosanitary treatment is the drop size spectrum, because an optimal droplet spectrum ensures the transfer of the required dose to the target; minimizes the off-target losses due to evaporation, drift, and run-off; and reduces worker's dermal and inhalation exposure. The first four papers in this Special Issue focus on the importance of drop size spectrum on pesticide applications. The first article, authored by [PERSON] et al., presents a laboratory low-cost test bench for testing agricultural spray nozzles [5]. The paper provides a comprehensive description of the test bench, its design, construction, advantages, and limitations during its functioning,as well as the results of some trials with an ATR80 orange hollow cone nozzle to test the functionality of the whole system. The measurement method is inspired by the ISO 5682-1 [6] and is based on the image analysis of droplets trapped inside a layer of silicone oil of suitable density and viscosity. The second article in this Special Issue, authored by [PERSON] et al., is strictly connected to the first one. It deals with the designing of two pneumatic spouts for vineyard applications capable of generating droplet size spectra in a wide range of options [7]. Through laboratory trials simulating a real sprayer, the paper assesses the influence of hose insertion position, liquid flow rate, and airflow speed on droplet size, homogeneity, and driftability. A proper combination of these parameters allows for varying the spray quality from very fine to coarse/very coarse, providing farmers with a wide range of options to match the drift-reducing EU policy requirements when using pneumatic sprayers and the treatment specifications for every spray application. The third article in this Special Issue, authored by [PERSON] et al., exploits the use of modified micro-emitters, usually used in greenhouse irrigation systems, in fixed agrochemical delivery systems composed of a network of micro-spravers/nozzles distributed in an apple orchard, replacing conventional hollow cone nozzles [8]. [PERSON] et al. found that all the usually assessed spray parameters, i.e., spray coverage, canopy deposition, spray uniformity, and ground and aerial spray losses, were all affected by droplet spectrum and worked better with the modified irrigation micro-emitters when compared to the hollow cone nozzles. In addition, the installation cost was greatly reduced. The fourth article in this Special Issue, authored by [PERSON] et al., evaluates the handler's exposure to pesticides from stretcher-type power sprayers in orchards [9]. Spray drop spectrum also plays a key role in operator dermal and inhalation exposure, together with the task being performed, target features, canopy structure, the amount of pesticide handled, the duration of the activity, the personal protective equipment used, the type of equipment used and its status, and others [10]. [PERSON] et al.