Application of pesticides is almost essential if one is to stay in the greenhouse profession. Eliminating weeds inside and outside the greenhouse reduces alternate hosts for ornamental plant pests. Screen doors and vents make it harder for moths and beetles to fly in and lay eggs or feed. But, careful as the grower may be, sooner or later an insect or mite will come in on the clothes of workers, on cuttings, in pots, or in soil. Despite these precautions, however, insects or other pests may become established.
Some growers treat whenever they discover pests.
Pesticides are applied in greenhouses in almost every conceivable manner. Since most pesticides are sensitive to ultraviolet rays, treatments made later in the evening will be more effective. After the waiting period specified on the label has passed, the structure must be well ventilated before workers can safely enter. Fogs, smokes, and aerosols are generally applied on a cubic-foot basis. For houses with flat, sloping roofs, add the height at the eave to the height at the highest part, divide by 2, and multiply by the area of the floor.