Pesticide Application in Vineyards
Vineyard Sprayers
Vineyard sprayers are not only used in vineyards to apply pesticides (i.e., insecticides and fungicides), but can also be used to apply liquid fertilizers or other liquid materials. Vineyard sprayers come in a variety of types, brands, sizes, and levels of complexity. Vineyard sprayers are classified mainly by how they deliver and distribute spray within the canopy. They fall into four main categories:
Hydraulic Sprayers (Conventional Pressure)
Hydraulic vineyard sprayers apply pesticides using a high-pressure hydraulic sprayer, without air assistance, equipped with a vertical boom for vineyard pest management. Insecticides and fungicides are often applied under high pressure because a finer spray is needed to obtain good coverage of the foliage. The working pressure is adjustable and depends on the specific pump and nozzle setup. A higher pressure generally leads to finer spray droplets, which can improve coverage but also increase the risk of pesticide drift. Vertical boom sprayers are used to spray through dense vine canopies where high-pressure sprays are necessary for adequate penetration and reach.
Air-Assisted Sprayers (Air-Blast, Air-Shear, or Pneumatic)
Most of the sprayers used in vineyards are in this category. The defining characteristic is a single large fan that assists with atomization and provides the primary transport mechanism for the droplets. Droplets discharged through hydraulic nozzles are blown by the air toward the target canopy. Without the fan’s air assistance (as is the case with hydraulic boom sprayers discussed previously), the droplets will likely not penetrate deep into the canopy. Air-assisted sprayers enhance canopy penetration and coverage by creating turbulence around the foliage, which in turn reduces spray volumes.
Air-Assisted Sprayer Configurations
Traditional airblast sprayers direct the air from a single axial flow fan, mounted directly behind the sprayer, in an upward and outward direction. Typically, the airblast sprayers are fitted with hydraulic or air-shear nozzles that provide a large amount of air to penetrate the canopy and beyond, often resulting in a vast plume of spray drifting above the target row. To minimize spray drift, growers typically use small, adjustable deflector plates fitted at the top and base of the air outlet to direct the air towards the target canopy.
Radial Discharge Airblast Sprayers. These sprayers are by far the most widely used in vineyards. The sprayer is equipped with a powerful fan (usually an axial-flow fan) mounted behind the sprayer as shown in Figure 26.3. The fan pulls the air from behind the sprayer and discharges it at a 90-degree angle away from the fan, and in a 180-degree arc that sprays the canopies on both sides of the sprayer. The spray liquid is introduced into this powerful airstream through a set of nozzles located inside the manifold or near the fan, where the air exits the fan. The rushing air shatters the liquid into tiny droplets that are carried towards the vine canopy. Faster air blasts produce smaller droplets. An increase in the liquid flow rate or a reduction in airblast causes the formation of larger droplets, while decreasing the liquid flow or increasing the air flow produces smaller droplets. Nozzles are placed radially in the output stream of air.
Directed Air Duct Sprayers. Low-volume, low-velocity air is produced by a relatively small fan with separate ducts delivering the air past each nozzle (Figure 26.4). Each outlet incorporates a nozzle surrounded by a stream of air. The airflow is convergent, creating excellent turbulence within foliage, which provides good coverage and reduces drift. The most significant advantage of these types of sprayers is the flexibility and accuracy they provide in adjusting the spray direction towards the canopy, or even towards a specific part of the canopy that requires protection against certain insects or diseases.
Tower Sprayers. Some hydraulic or air-shear nozzles can be fitted with a hollow “grape tower” to direct the air from the fan laterally to the vine canopy (Figure 26.5). Because spray clouds from tower sprayers can be directed horizontally or inclined toward the vine canopy, deposition can be more uniform than with a conventional airblast sprayer with a single fan operated from the vineyard floor.
Multi-Head Fan Sprayers. Multi-head sprayers (Figure 26.6) utilize several shrouded, small axial fans that can be independently adjusted to direct high-volume, low-velocity converging air streams to the canopy. These fans direct an airblast through hydraulic nozzles. Hydraulic nozzles are arranged behind or around the fans, allowing spray droplets to be caught up in the airstream and transported to the canopy. The location of the fans means that the point of atomization (the point of emission of the spray-laden air) is relatively close to the target.
Controlled Droplet Applicators
Controlled droplet applicators (CDA) have a single, shielded nozzle that atomizes the spray solution. This fine mist circulates within the shield, providing effective deposition. A brush skirt or plastic cover can be fitted over the shield to further reduce drift onto young vines, which are also fitted with break-back devices. CDA technology produces spray droplets that are relatively uniform in size, allowing the applicator to control droplet size.
Sensor-Controlled Applicators
Sensor-controlled applicators utilize optical sensors to detect the location of weeds within the vineyard. These sensors, coupled with a computer controller, regulate the spray nozzles and apply herbicides only when needed. A computer-controlled sensor detects chlorophyll in plants and then sends a signal to the appropriate spray nozzle, applying the herbicide directly to the weed, thus reducing herbicide use.
Electrostatic Sprayers
Electrostatic sprayers (Figure 26.8) utilize air-shear nozzles, where the solution (chemical and water) is combined through a “shearing” action, which atomizes the particles into extremely fine water droplets (< 50 µm). Then, just before the mist exits the nozzle, it is exposed to a high-voltage, low-current charge, usually at or near the nozzle outlet, producing electrically charged (negative) spray droplets. These droplets are carried into the vine canopy in a high-speed air stream. As the negatively charged droplets enter the canopy, they are attracted to the positively charged plant surface (opposite charges attract).
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