Depending on the crop, the size of the operation, the pesticide being
used, and the equipment available, greenhouse growers apply chemical
pesticides in one or more of the following forms:
• Systemics: These may be applied as soil drenches or as foliar sprays. They remain in the plant and kill the pest when it arrives.
• Sprays: The material is mixed with water in a hydraulic sprayer and applied to the foliage of the crop. A spreader/sticker agent may be needed to provide uniform coverage of the foliage. All parts of the plant must be covered or the untouched insects will remain alive. Careless or incomplete spraying accomplishes little more than temporary population reduction.
• Dusts: Coverage must be thorough, as with sprays. A duster can cover a large area of crops quickly and often at less expense than sprays. Many greenhouse pesticides are not available in dust form, however.
• Aerosol bombs: The pesticide material is packaged in a container with a propellant liquid or gas that disperses the pesticide uniformly through the greenhouse. The grower must calculate the cubic area of the greenhouse before use to ensure that the proper amount
of pesticide is applied. Aerosols are quick and easy to apply but expensive.
• Smoke fumigants: The pesticide is packaged with a flammable, smoke-producing material. When the container is lit, the smoke carries the pesticide throughout the greenhouse and to all parts of the crop. As with aerosols, the cubic area of the greenhouse must be calculated for correct application.
• Steam line vaporizers: The pesticide is painted onto cold steam lines, then all vents of the greenhouse are closed and the steam turned on. The chemical vaporizes and fills the house. Cubic areas must be calculated.
• Foggers: The grower must mix the pesticide in an oil solvent and fill the fogger. The fogger then heats the mixture, causing it to disperse uniformly. The oil can plug the machines, so thorough cleaning is important.
• Misters: The pesticide is mixed with a solvent that evaporates quickly once out of the mister. An air blast disperses the mixture in a fine mist.
Sprays and dusts often leave a residue of pesticide on the plant leaves that may prove objectionable to consumers. Certain systemics can remain invisible, yet toxic in the soil for many weeks. Their application must be discontinued far enough in advance of their sale to ensure that the plant product is safe for release to consumers. Growers who produce vegetables must take special care that no pesticides will remain active in the plant because eventually it will be consumed by humans.
Specific recommendations for greenhouse pest control are available from state colleges of agriculture and Cooperative Extension specialists. Many states also have active florist trade associations that share common problems and solutions through newsletters and statewide meetings. It is important for growers to take part in these associations.