Pests and Diseases
The same barrier that a greenhouse provides to keep out undesirable weather also keeps in pests and diseases. Greenhouse whiteflies (Trialeurodes vaporariorum) are primary pests that feed on sap and attack more than 250 plant types. They can be difficult to control because of their resistance to most pesticides. Before reaching maturity, whiteflies progress through seven life stages. Eggs and pupae do not succumb to insecticides, which kill nymphs and adults. Neem and horticultural oils manage immature stages and pyrethroid insecticides control adults. The humid greenhouse conditions that many plants favor also promote diseases, which is another reason for installing an adequate ventilation system.