As noted in Chapter 6, the most current approach to pest control in greenhouses is integrated pest management. IPM is a step back from total reliance on pesticides to play the lead role in profitable control. As the number of approved pesticides diminishes and the resistance of insects and pathogens increases, the chemical control of pests is declining in its effectiveness. Also, as concern for the natural environment grows, pesticides are no longer blindly accepted by everyone. Many growers share the concern of nonhorticulturists about the excessive, indiscriminate use of pesticides in the past.
Integrated pest management in greenhouses uses temperature and humidity control, resistant varieties, screens and other entry barriers, monitoring devices, predatory insects, and pesticides to keep pest problems below an economic damage level. Pesticides are applied only when the pest is most vulnerable and then only where needed. They are not necessarily broadcast through the entire greenhouse.
IPM is costly in terms of the time required to monitor insect and disease development within a crop, as well as the expense of the predatory inoculum. Both costs are ongoing. Greenhouse crops may require careful, methodical inspection twice each week. That can include looking under leaves and/or lifting the pots of sampled plants to find insects in their hiding places. Yellow sticky cards, placed at regular intervals throughout the crop, can help the grower survey the type of insects present in the greenhouse and their stages of development (Figure 20-17). The cards are changed weekly. All data concerning the type and number of insects are recorded, along with observations of disease symptoms and the areas where the pests are located within the crop. Such data permit the grower to select the best and most cost-effective means of control while targeting the area(s) of the crop where it should be applied.
figure 20-17. Checking the yellow sticky card regularly helps a grower monitor insect numbers and stages of development. (Delmar/Cengage Learning. Photo by Steven Newman.)
To incorporate fully a program of IPM in a greenhouse necessitates the following:
• elimination of weeds throughout the greenhouse
• a program of sanitation throughout the structure to include bench and/or container pasteurization
• thorough inspection of all plant materials before bringing them into the greenhouse
• screening of all vents, doors, and other openings to the outdoors
• regular, ongoing scouting to identify, quantify, and record the presence and location of pests within the crop
• control of the greenhouse environment to favor the crop rather than the pests
• application of the principles of control to include biological control methods that can reduce the amount and frequency of chemical pesticide application
Integrated pest management requires a heavy commitment of time in monitoring the crop and the recurring expense of purchasing and releasing beneficial predators into the greenhouse environment. However, the savings in pesticide costs and the reduced occurrence of pesticide resistance and chemical injury to crops can offset that expense.
