4.1 Application Equipment Types & Operation

4.1 Application Equipment Types & Operation

Selecting, operating, and maintaining proper pesticide application equipment is fundamental to effective pest management, environmental protection, and regulatory compliance. Pesticide application equipment ranges from small hand-operated backpack sprayers to massive self-propelled agricultural boom sprayers, commercial chemigation systems, space-treating thermal foggers, and specialized soil injection rigs. Applicators must thoroughly understand the mechanical components, operating principles, and safety requirements of their equipment to deliver target chemical dosages accurately while preventing equipment failure, chemical spills, and off-target contamination.

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Overview of Application Equipment Types

Different pest management scenarios demand specialized delivery systems engineered for specific chemical formulations and target site characteristics:

1. Hydraulic Sprayers

Hydraulic sprayers use liquid pressure created by a pump to force spray mixture through nozzle orifices, breaking the liquid stream into droplets. They are the most versatile and widely used application devices in agriculture, forestry, turf, and rights-of-way:

• Boom Sprayers: Feature a horizontal pipe or truss (boom) fitted with multiple evenly spaced nozzles. They are designed for broadcast applications over broad areas, such as field crops, pastures, and turf grass. Booms can span from 15 feet on small utility vehicles to over 120 feet on commercial agricultural rigs.
• Boomless Sprayers: Utilize a specialized central cluster nozzle or cluster of nozzles to throw a wide swath of spray without a physical boom arm. They are ideal for rough terrain, orchard understories, and brushy rights-of-way where physical booms would strike trees or fence posts. However, boomless sprayers are highly susceptible to wind drift and yield less uniform spray patterns than boom sprayers.
• Backpack & Small Manually Pressurized Sprayers: Consist of a 1- to 5-gallon tank, a hand-operated lever pump or compressed air cylinder, a short hose, and a hand wand with a single nozzle. Used primarily for spot treatments, structural perimeter barriers, small gardens, and localized weed patches.

2. Air-Assisted Sprayers, Misters & Thermal Foggers

• Air-Assisted (Air-Blast) Sprayers: Use a hydraulic pump to deliver liquid to nozzles positioned in front of a powerful fan. The high-velocity airstream atomizes liquid into fine droplets and carries them deep into dense fruit tree canopies or vineyard vines. Because droplets are fine and propelled by air, drift potential is exceptionally high.
• Misters & ULV (Ultra-Low Volume) Foggers: Generate extremely small droplets (10 to 50 microns) for space treatments, public health mosquito control, and greenhouse pest management. Thermal foggers use heated engine exhaust or pulse-jet tubes to vaporize chemical solutions into dense fogs.

3. Granular Spreaders & Soil Injection Units

• Granular Drop Spreaders: Release dry granules through adjustable metering orifices along the bottom of a hopper. Granules drop straight down by gravity directly between the wheels, providing precise swath boundaries with zero wind drift.
• Granular Rotary (Centrifugal) Spreaders: Drop granules onto a spinning horizontal disk that throws granules outward in a wide semi-circular arc. Rotary spreaders cover large areas rapidly but require overlapping passes to maintain uniform distribution across the swath.
• Soil Injection & Termiticide Rigs: Utilize high-pressure positive-displacement pumps connected to soil injection rods or sub-slab injectors to treat subterranean soil zones around foundations or trees.

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Chemigation Systems & Nevada Safety Mandates

Chemigation is the practice of applying agricultural chemicals (pesticides or fertilizers) directly through an irrigation system (such as center-pivot, lateral-move, drip, or solid-set sprinkler systems). While chemigation offers high operational efficiency, it poses an extreme point-source contamination risk to groundwater wells and surface streams if chemical back-siphoning occurs.

Under Nevada Revised Statutes (NRS 555) and Nevada Department of Agriculture regulations, any irrigation system connected to a groundwater well or surface water source used for chemigation must be equipped with a mandatory anti-siphon/backflow safety assembly:

1. In-Line Main Check Valve: A heavy-duty, spring-loaded check valve located in the main irrigation pipeline downstream from the water pump to prevent water-pesticide mixture from flowing backward into the water source.
2. Vacuum Relief Valve: Installed on top of the main pipeline between the water pump and the main check valve. It automatically opens to admit air into the pipe whenever pump pressure drops, breaking any suction vacuum that could pull chemicals back into the well.
3. Automatic Low-Pressure Drain: Located on the bottom of the main pipeline upstream of the check valve. If the main check valve leaks while the pump is shut down, chemical solution drains harmlessly onto the ground rather than leaking past the valve into the wellhead.
4. Chemical Injection Line Check Valve: A positive displacement, spring-loaded check valve (minimum 10 psi opening pressure) in the chemical injection line to prevent irrigation water from flowing backward into the pesticide supply tank, and to prevent gravity flow of pesticide into the irrigation pipe when the injector stops.
5. Interlocking Power System: The chemical injection pump must be electrically or mechanically interlocked with the main irrigation water pump so that if the water pump stops, the chemical injection pump automatically shuts off immediately.

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Sprayer Components: Pumps, Agitation & Filtration

A hydraulic sprayer represents a closed mechanical circuit. Understanding component function is vital for troubleshooting and maintenance:

1. Pump Selection & Operating Characteristics

The pump is the heart of the hydraulic sprayer, moving liquid from the supply tank to the nozzles under pressure. Pumps are classified into positive displacement and non-positive displacement designs:

• Roller Pumps: Positive displacement pumps utilizing flexible rollers rotating inside an eccentric housing. Compact and low cost; operate at pressures up to 300 psi with flow rates of 10-30 GPM. However, abrasive wettable powder (WP) suspensions rapidly wear out the rollers and housing.
• Centrifugal Pumps: Non-positive displacement pumps utilizing a high-speed rotating impeller. Deliver extremely high flow rates (up to 120 GPM) at lower operating pressures (typically 20-70 psi). They handle abrasive suspensions effortlessly and require simple maintenance, but are not self-priming and cannot generate high pressures.
• Diaphragm Pumps: Positive displacement pumps where flexible diaphragms seal fluid chambers. Produce moderate-to-high pressures (50-850 psi) and moderate flow rates (5-60 GPM). Synthetic diaphragms isolate moving mechanical parts from spray chemicals, making them highly resistant to corrosive and abrasive formulations.
• Piston Pumps: Positive displacement pumps utilizing reciprocating pistons. Deliver high operating pressures (up to 1,000 psi) at lower flow rates (2-25 GPM). Highly durable and self-priming; ideal for high-pressure handgun spraying and orchard tree applications.

2. Agitation Systems

Pesticide formulations (especially wettable powders, dry flowables, and liquid suspensions) require continuous agitation inside the spray tank to prevent chemical settling:

• Hydraulic Jet Agitation: Uses bypass fluid returned from the pressure regulator. Liquid is forced through jet agitator nozzles mounted at the bottom of the tank. Requires high pump capacity—typically 20% of total pump output must be dedicated to hydraulic agitation.
• Mechanical Paddle Agitation: Utilizes a revolving horizontal shaft fitted with paddles or propellers running through the tank bottom. Mechanical agitation provides violent physical mixing required for heavy wettable powder suspensions and large tanks (> 500 gallons).

3. Filtration & Strainer Mesh Sizes

System strainers prevent abrasive debris and undissolved chemical clumps from damaging pump components or clogging nozzle tips. Mesh size refers to the number of openings per linear inch; higher mesh numbers indicate finer filtration:

• Suction / Intake Strainer (50-mesh): Installed on the suction line between tank and pump intake to protect internal pump gears from coarse sand and rust scale.
• Main Line Strainer (50-mesh): Installed downstream of the pump and pressure regulator to capture fine debris before liquid reaches the boom manifold.
• Nozzle Strainers (50 to 100-mesh): Individual slotted or mesh strainers placed directly behind each nozzle tip. Fine flat-fan nozzles (< 0.2 GPM output) require 100-mesh strainers to prevent tip clogging.