5.1 Agricultural Application Equipment Types

5.1 Agricultural Application Equipment Types

Choosing the right application equipment is fundamental to ensuring that pesticides are delivered safely, efficiently, and effectively to the intended target. The choice of equipment depends significantly on the formulation of the pesticide (e.g., liquid, granular), the target pest or crop, the size of the area to be treated, and environmental considerations. Application equipment can range from simple handheld devices for spot treatments to complex, tractor-mounted machinery designed for large-scale agricultural production. Understanding the mechanics, advantages, and limitations of each type is a core competency for any certified applicator.

Hydraulic Sprayers

Hydraulic sprayers are the most common type of liquid application equipment used in agriculture. They rely on liquid under pressure to atomize the spray mixture into droplets and force them out through a nozzle. The pressure is typically generated by a pump driven by a tractor's power take-off (PTO), a separate engine, or an electric motor. The primary components of a hydraulic sprayer include a tank, pump, agitator, strainers (filters), pressure gauge, pressure regulator, control valves, hoses, and nozzles.

Boom Sprayers

Boom sprayers are hydraulic sprayers equipped with a horizontal boom that supports multiple nozzles spaced evenly along its length. They are primarily used for applications on large areas of flat land, such as row crops, pastures, and turf. The boom allows for the rapid treatment of wide swaths in a single pass. Boom sprayers can be configured for several types of applications:

• Broadcast Application: The goal of a broadcast application is to apply a uniform coating of pesticide across the entire surface of a field. The nozzles on the boom are positioned and spaced to provide overlapping spray patterns, ensuring even coverage. This method is frequently used for applying pre-emergent herbicides or broadcasting fertilizers and soil amendments.
• Band Application: In a band application, the pesticide is applied in narrow strips (bands) directly over or alongside the crop rows, rather than covering the entire field surface. This technique is often used to control weeds specifically within the crop row while leaving the space between rows untreated (which might be managed mechanically). Banding significantly reduces the total amount of pesticide used per acre, lowering costs and environmental impact.
• Directed Application: Directed applications target the pesticide specifically at the pest or a precise portion of the crop, avoiding other areas. For example, herbicides can be directed at the base of a woody plant or below the crop canopy to avoid injuring the crop leaves. This requires specialized nozzles, drop tubes, and careful calibration of boom height.

Backpack and Handheld Sprayers

Backpack (knapsack) and handheld sprayers are small, portable hydraulic sprayers ideal for small-scale applications, spot treatments, and working in areas inaccessible to larger machinery.

A typical backpack sprayer consists of a 3- to 5-gallon tank, a hand-operated pump, a pressure chamber, a hose, a wand, and a single nozzle or a small boom. The applicator pressurizes the system by manually pumping a lever. While versatile and inexpensive, they require significant physical effort and are not suitable for large acreages. Constant attention to walking speed and pumping rhythm is necessary to maintain a uniform application rate. They are frequently used for applying herbicides along fence lines, treating individual invasive plants, or managing pests in small greenhouses.

Airblast Sprayers (Orchard/Vineyard)

Airblast sprayers, also known as air-carrier sprayers, are the standard equipment for applying pesticides in orchards, vineyards, and dense foliage crops where canopy penetration is critical.

Instead of relying solely on liquid pressure to carry droplets to the target, airblast sprayers use a powerful fan to generate a high-velocity stream of air. The liquid pesticide is delivered at relatively low pressure to nozzles located in or near the air stream. The air stream shears the liquid into very fine droplets and transports them deep into the plant canopy.

The turbulence created by the air stream causes leaves to flutter, exposing both the upper and lower surfaces to the pesticide, which is crucial for controlling many insects and diseases. However, the fine droplets and strong air currents make airblast applications highly susceptible to spray drift. Operators must carefully manage fan speed, travel speed, and nozzle orientation based on wind conditions and canopy density. In modern orchard management, tower sprayers or directed airblast designs are often used to better target the air stream and reduce off-target drift.

Granular Applicators

Granular applicators are designed to distribute dry, solid pesticide formulations (granules) uniformly over a target area. Granules are often used for soil-applied insecticides, nematicides, and pre-emergent herbicides. Because the pesticide is bound to a dry carrier, water is not required for application, which simplifies the equipment.

Drop Spreaders

Drop spreaders consist of a hopper (tank) with a row of adjustable openings across the bottom. A rotating agitator inside the hopper ensures a steady flow of granules, which drop straight down by gravity onto the soil surface.

• Advantages: Drop spreaders provide an extremely precise application pattern with distinct, sharp edges. They are minimally affected by wind, making them ideal for applying herbicides near sensitive borders or ornamentals.
• Disadvantages: The swath width is limited strictly to the physical width of the spreader hopper. Applying granules over a large area with a drop spreader requires many passes and is time-consuming.

Rotary (Centrifugal) Spreaders

Rotary spreaders, also known as broadcast spreaders, drop granules from the hopper onto a spinning horizontal disc (impeller). The centrifugal force flings the granules outward in a wide, semi-circular pattern.

• Advantages: Rotary spreaders can cover a much wider swath than their physical width, allowing for rapid application over large areas (e.g., broadcasting fertilizer or granular herbicides over a large pasture or turf area).
• Disadvantages: The application pattern is less precise, with the distribution being heaviest in the center and tapering off toward the edges. To achieve uniform coverage, the operator must overlap swaths carefully. The flying granules are also more susceptible to wind displacement compared to drop spreaders.

Chemigation and Fertigation Systems

Chemigation is the process of applying pesticides (including insecticides, herbicides, and fungicides) through an irrigation system. Fertigation is the application of fertilizers through the same method. This technique integrates pest management with routine crop watering, saving time, labor, and fuel.

Common irrigation systems used for chemigation include center pivots, linear move systems, micro-sprinklers, and drip irrigation networks. The pesticide is typically injected into the main irrigation line using a specialized chemical injection pump.

Backflow Preventer Requirements

The most critical environmental and safety concern associated with chemigation is the potential for the pesticide mixture to flow backward (siphon) into the water source (e.g., a well, stream, or municipal water supply) if the irrigation pump unexpectedly shuts down or if there is a sudden loss of water pressure.

To prevent this catastrophic contamination, stringent regulations mandate the installation of specialized anti-siphon devices on all chemigation systems. A complete backflow prevention assembly typically includes:

1. Check Valve: A primary mechanical valve in the main water line that closes automatically when water flow stops, preventing backward movement.
2. Low-Pressure Drain: Located upstream of the check valve, this drain opens automatically when the water pressure drops, allowing any fluid that leaks past the check valve to drain safely onto the ground rather than into the water source.
3. Vacuum Relief Valve: Located between the pump and the check valve, this valve allows air into the pipe when the pump shuts off, breaking the siphon effect that could otherwise pull chemicals back into the water supply.
4. Interlocking Controls: Electrical systems must interlock the chemical injection pump and the irrigation water pump so that if the water pump fails, the chemical pump immediately stops injecting pesticide.

Understanding these distinct types of application equipment is essential not only for achieving effective pest control but also for mitigating environmental risks and ensuring operator safety.