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In most pest management programs on greenhouse crops, growers can benefit from using insecticides, which can prevent the manifestation of large pest numbers and reduce pest populations. Even if the plants don’t die, pests can still damage plants and decrease their salability to prospective customers.

Common insecticides for greenhouse use include:

Contact insecticides

Contact insecticides can be used directly on pests or on surfaces that will affect pests when they meet the surface.

Stomach poison insecticides

When pests feed on a leaf or other surface that has been treated with an insecticide, the pests absorb the residues of that insecticide through the stomach lining. Pests usually die within two to four days.

Translaminar insecticides

Translaminar insecticides treat pests that foliar-feed on leaves by building up a reservoir of active ingredient inside the leaf.

Systemic insecticides

Systemic insecticides are applied to the growing medium as a drench or granule, and the plant takes up the active ingredient through its root system. These insecticides prevent phloem-feeding insects from developing large populations.

General insecticide tips

Many insecticides that are used on insects are either broad-spectrum or narrow-spectrum/selective. Broad-spectrum insecticides treat multiple types of insects, while narrow-spectrum insecticides are designed to treat specific insects.

When treating insect pests with insecticides, applicators should thoroughly treat all above-ground plant parts, including both the leaf tops and undersides, the latter of which where many insects reside.

Growers and applicators should routinely set up water-sensitive paper or spray cards to determine spray coverage.

Growers should also time insecticide applications for when insect pest populations are low. Most pests are active in the early morning or late afternoon, when most insects are active.

Most insecticides do not kill the eggs or pupae stages of insects, so applicators should perform repeat applications to kill those insects when they are in later stages of growth. When there are large insect populations, growers may need to make two or three applications.

Seasonal factors also determine insecticide application best practices. Under cool temperatures, the insect life cycle is longer than under warm temperatures. Applicators may not need to make as many insecticide applications as in cool seasons, but the time that passes between spray applications in those seasons is often too long to be effective.

Source: “Don’t let pests prevail,” by Raymond Cloyd, Greenhouse Management, February 2016