Pesticide Application and Equipment in Greenhouses
Methods of Pesticide Application
When applying pesticides, coverage is everything. Even the most effective new pesticide or fungicide is useless unless it comes in contact with the insect or disease it has been formulated to control. There are numerous methods of chemical applications available to greenhouse growers. The three primary types of sprayers used in greenhouses are: (1) high-volume sprayers, (2) low-volume sprayers, and (3) ultra-low volume sprayers. Each of these machines has their place in greenhouse chemical application. They all have advantages and disadvantages. Primary differences among sprayers are the quantity of water used, the operating pressure, and the size of droplets produced.
High Volume Sprayers
High-volume sprayer uses a high flow rate of water to wet the foliage to the point of runoff. A pump supplies energy that carries spray material to the target (plant foliage). This sprayer uses standard rates of chemicals and large volumes of water. The quantity of water to use depends on the specific sprayer and nozzle, the spraying technique of the operator, and the size of the crop. Calibrating the sprayer according to the operator and the crop is essential for mixing the correct amount of spray mix. The hydraulic sprayer can do a good job of covering foliage.
Backpack Sprayer
The tank in this sprayer holds about 4 gallons of material (Figure 30.9). A hand-operated pump pressurizes the spray material as the operator walks along, and the wand with nozzle directs the spray to the target.
Skid-Mounted Sprayer
With a tank size up to 200 gallons (757 L), these sprayers will fit onto an all-terrain vehicle (ATV) or electric cart.
Irrigation Boom Sprayer
With increasing production in plug and cell trays, the use of the boom sprayer has become an important tool for getting uniform watering. By installing three-way turrets with nozzles for irrigation, misting and pesticide application, one piece of equipment serves multi-purposes.
Central Pesticide Application System
In gutter-connected ranges, it is possible to install a piping system that will deliver pesticides to any part of the greenhouse. Pesticide preparation and filtration are done in a mixing area. A single pump and piping that will handle the pressure developed are required.
Low-Volume Sprayers
A low-volume sprayer uses less water or carrier to apply insecticides, fungicides, disinfectants and even fertilizers to greenhouse crops. Targeted low-volume sprayers create droplets with an average diameter of between 40 to 70 microns utilizing high pressures between 1,000 and 3,000 psi. These high pressures create fine droplets with high velocity. This velocity is easily diffused once the spray cloud hits the target, creating a swirling spray cloud with a tremendous amount of turbulence in reaching the internal foliage.
Air-Assisted Sprayers
Low-volume sprayers, particularly air-assisted sprayer, are well-suited for greenhouse applications. The fine droplets and increased airflow help reach the innermost parts of the canopy, ensuring thorough coverage and effective pest and disease control. Air-assist (air-shear) technology uses high velocity airflow to improve the atomization, transportation, penetration, and deposition of spray products. The fan’s powerful, high-volume air flow efficiently transports the droplets to the target canopy while also creating a turbulent environment in the canopy. This results in uniform coverage of the upper and undersides of the target leaves while penetrating both horizontal and vertical directions in the canopy.
Air-Assisted Electrostatic Sprayers
The heart of the air-assisted electrostatic sprayer is the patented “air-atomizing induction-charging” nozzle, which was invented and refined at the University of Georgia (Figure 30.10). Air and liquid enter the rear of the nozzle separately. The air moves through the nozzle at a high speed and intersects the liquid at the nozzle tip, causing the formation of spray droplets that are 30 to 60 microns in diameter. The air pressure required is 15 to 60 psi, and the liquid pressure is below 30 psi. In comparison, a hydraulic sprayer would require nearly 3,000 psi to achieve equivalent atomization. As the spray is atomized, the droplets pass an electrode that induces a negative charge on each one. The force of the turbulent air stream then propels the charged droplets deep into the plant cover.
Controlled Droplet Applicators
Controlled droplet application (CDA) is a term used to describe a new method of applying pesticides (Figure 30.11). The efficiency of CDA enables the use of low and ultra-low volumes of spray liquid. Controlled droplet application technology uses centrifugal force instead of hydraulic pressure to produce with a narrow range of droplets of the same size. Conventional spray nozzles produce droplets that vary widely from small droplets that may drift or evaporate before reaching the target, to large droplets that concentrate too much of the pesticide in one spot.
Ultra-Low Volume Sprayers
Ultra-low volume (ULV) sprayers include high-pressure cold foggers and thermal foggers. Both use very low volumes of spray, delivering small spray droplets that can penetrate crop foliage. These are the machines most commonly called sprayers. Ultra-low-volume systems generally use very small quantities of water and generate spray droplets smaller than 25 microns in diameter. This is a true fog, often resulting in a slight haze in the greenhouse. Ultra-low volume applications will not raise greenhouse humidity and are a good choice when days are short and nights are long.
Total Release Aerosol Canisters
Total release aerosol canisters can be set into a greenhouse, actuated, and allowed to fill the greenhouse (Figure 30.12). Once a canister is activated, this propellant force the spray solution through the nozzle atomizing solution into a cloud. The pesticide is delivered in small droplets, which drift throughout the greenhouse and finally settle on the plants and target pests. Because these systems have no lateral movement created by the canister, they must rely heavily on HAF fans to provide even coverage on all plant surfaces.
Cold Foggers
Cold foggers use turbulence in the fogging nozzle to shear liquid into small droplets (Figure 30.13). The typical air source is a high velocity fan, usually integrated with the fogging nozzle. The high air pressure produced by the motor helps to spray the fogging liquid through the nozzle separating it into tiny particles. The liquid solution gets sprayed out of the nozzle in form of a fog or a fine mist. There is no need for liquid pressure. In most cases, the atomization nozzle doesn't have any small orifices, so nozzle plugging is not a problem. These applicators produce a droplet size between 5 and 20 microns.
Thermal Foggers
A thermal fogger uses a system like that used in jet engines (Figure 30.14). The pesticide is injected into the extremely hot, fast moving air stream, where it is vaporized into fog-sized particles. Foggers generate very small drops, usually less than 0.05 to 20 microns in diameter, that can move long distances from the applicator. This means the spray can penetrate far into the structure rather than settling near the spray unit. The rate of application depends on the size of the metering orifice. Thermal foggers that are designed to treat larger areas have large tanks and require more time to dispense the greater volume of pesticide mixture. The defining characteristic of thermal foggers is their spe
Mechanical Aerosol Generators
These sprayers use air-atomizing nozzles with air supplied by an air compressor to disperse the spray liquid into small drops. Air also is the main method of moving the spray around the greenhouse and onto the foliage. Much of the spray movement is accomplished by the greenhouse air movement system, e.g., horizontal air flow (HAF) fans.
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