Chapter 21

Integrated Pest Management for Greenhouse Crops

Monitoring for Crops Pests

Monitoring (scouting) is a basic component of IPM programs. Monitoring is the regular inspection of greenhouse crops and growing areas for pests, including insects, pathogens, nematodes, and weeds. Monitoring includes the following: 1) making accurate identifications of pests and related crop injury present in the field, 2) determining the abundance of the pest populations, 3) recording crop stage and management practices, and 4) carefully recording all field observations. Monitoring provides many advantages. It serves as an early warning system for the presence of pests and diseases. This allows for the implementation of appropriate pest control strategies before pest populations and diseases escalate. Furthermore, regular monitoring allows for the evaluation of pest management control actions, including the use of natural enemies.

Scouting Frequency

A weekly monitoring program is typically adequate for most greenhouse situations. More frequent monitoring may be deemed necessary for high value crops or for pest-prone or pest-infested areas. Plugs should be inspected every 3 to 4 days. The scout should have thorough knowledge of the pest complex for the specific crop varieties of the greenhouse and have some basic education in plant and pest biology.

Scouting Pattern

Scouts should establish a pattern that will cover all areas of the greenhouse and follow the same pattern every time. Scouting should start from a major doorway. This is often the location where disease and pest problems begin. Special attention should be paid to plants around any openings in the greenhouse, especially those plants on the outside rows of benches. Scouts should walk every aisle and move from bench to bench in a snake-like or zig-zag pattern. At least three plants on every bench should be inspected, from the edge, the middle and as far into the bench as can be reached.

Pest Monitoring Techniques

Various pest monitoring techniques are used to monitor pests in the greenhouse. The type of technique selected will largely depend on the potential pest complex of the plants to be protected. Some pests are somewhat universal and can be monitored using conventional methods such as sticky traps or visual observation of plant parts. Other pests require unique monitoring methods such as the use of a pheromone that is typically very selective for a particular pest species.

Visual Observation

Visual observation can be useful to determine the presence of pests. The most common way to determine if pests are present is to search for the presence of pests on leaves, stems, or other plant parts. This strategy is best for aphids, spider mites, some psyllids, and other arthropods that do not fly readily when the plant part (or sampling unit) is counted or removed. This method can also be used for immature stages of pests, such as immature whiteflies. Visual observation can be very subjective, so it’s important that the same person monitors the crop throughout the season.  That means regularly checking plants in a number of different areas of the greenhouse. One good way to do this is to follow a zigzag pattern each time you do a visual inspection. Randomly choose plants to inspect along the way.

Sticky Traps

Sticky traps are efficient and important monitoring tools that can alert growers to the early presence of pests, indicate hot spots and insect migration patterns, and provide other information that can be used in control strategies (See Figure 21.1). Sticky traps are used to monitor flying pests such as adult whiteflies, thrips, fungus gnats, shore flies, leaf miners, psyllids, winged aphids, and leafhoppers. The traps come in two colors, a bright yellow and a medium blue. The yellow traps attract flying aphids, fungus gnats, whiteflies, leafminers, thrips, and other insects. Blue sticky traps are used primarily to attract thrips. Most greenhouses use the yellow traps which attract flying aphids, fungus gnats, whiteflies, leafminers, thrips, and others. Blue sticky traps are used to attract mainly thrips. These brightly colored cards are covered with a sticky substance that traps the insects. Insect and mite pests not captured on sticky cards include: non-winged aphids; mites including two-spotted spider mite; broad mite and cyclamen mite; mealybug immatures and adult females; scale immatures and adult females; and egg, larva/nymph and pupa stages of many greenhouse insect and mite pests.

Pheromone Traps

Insects secrete pheromones to alert other insects about information such as the sex of the insect, trail location, alarm, and grouping. Synthetically produced pheromones mimic the chemicals produced by insects and are used to lure specific insect species to specially-designed traps (See Figure 21.2). Pheromone traps can be used to: 1) detect early pest infestations, such as the first occurrence of migratory pests, 2) define areas of pest infestations, 3) track the buildup of a pest population, and 4) help in decision making for insect pest management. Since pheromone traps are relatively easy to use and inexpensive, species specific, and environmentally benign, they make ideal tools for IPM programs.

Indicator Plants

Indicator plants are highly susceptible host plants (Table 21.1). They are often grown purposely, either among the commercial crop or at the edge of the crop/benches in the greenhouse. Since these indicator plants are the first plants to become infested/infected, the scout knows that the adjacent main crop may be attacked soon. Indicator plants therefore aid in predicting pest problems. For example, peppers and eggplants are prone to aphid and thrips infestations.

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