Chapter 25

Pesticide Application and Equipment in Greenhouses

Methods of Pesticide Application

The three primary types of sprayers used in greenhouses are: 1) hydraulic or high-volume hydraulic sprayers, 2) targeted low-volume sprayers, and 3) fog or ultra low volume sprayers. Each sprayer has a purpose; a greenhouse operation will require two or more types of sprayers for various tasks. Primary differences among sprayers are the quantity of water used, the operating pressure, and the size of droplets produced.

Hydraulic Sprayers

A hydraulic or 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. Typical hydraulic sprayers usually operate at pressures between 100 to 300 psi, output between 2 and 4 gallons per minute and have average particle sizes between 200 and 400 microns. Insecticides and fungicides are applied at higher pressures— more than 60 psi—to achieve droplets of 100 microns or less in diameter.

Types of Hydraulic Sprayers

  • Compressed air sprayer
  • Backpack sprayer
  • Skid-mounted sprayer
  • Irrigation boom sprayer
  • Central pesticide application system

Targeted Low-Volume Sprayers

The most common way of applying pesticides in greenhouses is with high-pressure, high-volume hydraulic systems. Despite the well-documented evidence that less than one percent of the active ingredient applied through wet spraying actually reaches the target pest, the ease and familiarity of this application method makes it routine among growers. Likewise, pesticide labels consistently reinforce this application technique and have contributed to the continued dominance of dilute sprays in the greenhouse. However, the low-volume systems are gaining favor with an increasing number of growers who see the potential to increase spray deposition, improve efficacy, and reduce application rates and times. A low-volume sprayer uses less water to apply chemicals and fertilizers. 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.

Types of Targeted Low-Volume Sprayers

  • Backpack mist blower
  • Air-assisted low-volume sprayers
  • Electrostatic sprayers
  • Rotary disk sprayer

Fog or Ultra-Low Volume Sprayers

These are the machines most commonly called foggers. Ultra low-volume (ULV) systems generally use very small quantities of water (0.5 gal, 2 L per 10,000 square feet) and generate spray droplets smaller than 25 microns in diameter. This is a true fog, often resulting in a slight haze in the greenhouse. Because of the small particle size, ULV sprayers need to be used in an enclosed space to contain the spray solution. For best results with this method, proper air circulation is necessary.

Types of Fog or Ultra Low-Volume Sprayers

  • Mechanical foggers
  • Thermal foggers
  • Total release aerosol canisters

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