Chapter 26

Integrated Pest Management in Greenhouses

Cultural Pest Control in Greenhouses

Cultural pest control involves activities or practices that either enhance crop growth or alter a pest’s (e.g., insects, diseases, weeds) habitat—in this case, the crop production environment in the greenhouse—so that it is less favorable to a pest. Most of the time, cultural control is used as a preventative measure. By anticipating pest problems before they occur, the control techniques avoid or minimize the pest’s impact on the crop. Cultural control techniques are most effective when the target pests have few suitable host plants, do not disperse far or frequently, and/or have complex nutritional or environmental requirements during their life cycle. Pests may be thwarted by managing the greenhouse environment, adjusting planting schedules, rotating crops, fallow periods, or discarding infested plants. Some of these techniques are further explained below.

Managing the Greenhouse Environment

Environmental factors such as light, air temperature, plant temperature, relative humidity, air circulation, media composition, pH and electrical conductivity, as well as the nutritional status of the crop, impact both the health of the plants and the pests that attack them. The use of environmental controls to manage diseases is complex because of the simultaneous effect on crop production. It is important to understand the cultural and environmental requirements of the crops being produced. Chronically stressing plants, for example, by growing them under conditions that are too dry or too wet can make them more susceptible to attack by disease pathogens. Spider mites, in particular, favor dry environments.

Separate Growing Facilities

Use separate greenhouses for vegetable plants and ornamental plants to protect vegetable plants from tospoviruses; protect cucurbit seedlings from powdery mildew and to make it easier to treat vegetable plants if pesticides are needed. Viruses in the genus Tospovirus cause significant worldwide crop losses. The genus name is derived from the name of its first member, Tomato spotted wilt virus (TSWV).

Weed Control

The goal of weed control is to eliminate all possible sources of pest contamination in and around the greenhouse. Weeds inside and near the outside of the greenhouse can harbor pests. A weed-free fabric groundcover or concrete floor under greenhouse benches can also be instrumental in preventing problems. In contrast, having bare soil under plants can allow soil pathogens to splash or blow onto nursery plants and can be a favorable environment for weeds. Weeds near or under benches may provide cover for insect pests including thrips, aphids, whiteflies, and weevils.

Fallow Periods

If growers keep their greenhouses full year-round, they will have pests in them continuously. However, scheduling a one- or two-week break between crops in their greenhouses can greatly help to reduce pest populations. An empty greenhouse provides no food for any pests still remaining (assuming, of course, that there are no weeds present).

Pruning and Rouging

Discarding infested or diseased plants sometimes is more cost effective than using a chemical control. An effective way to manage some pests on plants is pruning. For example, removing the lower leaves of poinsettias, after a healthy upper canopy develops, often reduces whitefly numbers. Rouging is also a very good method to use if you find diseased or pest infested plants because you can just simply pull them out and dispose of them properly.

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