Chapter 26

Integrated Pest Management in Greenhouses

Monitoring for Crops Pests

Monitoring (also called scouting) is a basic component of integrated pest management (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 greenhouse observations. Monitoring provides many advantages. It serves as an early warning system for the presence of pests and diseases.

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 cards 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 pest species. Since all methods only estimate the number of individuals in the actual population, there is always variation from one sample to the next.

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 several different areas of the greenhouse.

Signs of Plant Damage. When scouting, look for obvious signs of plant damage, such as chlorotic, stunted, or malformed growth, cast-off skins, feeding damage, honeydew, sooty mold, and the presence of ants. Using a 10X magnifying hand lens, check the undersides of leaves from the top to the bottom of the plant to detect infestations before they cause severe plant damage.

Number of Sampling Points. In many cases there are no specific requirements for how many locations or plants to be monitored. The number of plants inspected will depend on factors such as the value of the crop, potential problems and size and type of greenhouses. The more plants or locations inspected, the more likely the sooner a problem will be detected, when management is easiest. In practice, scouting is a compromise between thoroughness (examining everything), efficiency (putting limited time to the best use), and cost (the value of improved management information).

Evaluating Biological Control Measures. Visual sampling is also a good way to record the presence of natural enemies and evaluate biological control in conservation and augmentation programs. This includes examining plants for predators such as ladybird beetle adults and larvae, syrphid fly larvae, lacewing larvae, and spiders.

Scouting Frequency. By inspecting the greenhouse on a systematic basis, pests that arise can be controlled before populations become economically intolerable. A weekly monitoring program is typically adequate for most greenhouse situations.

Scouting Pattern. Scouting must be done in a thorough manner to be successful. The number of plants, their size, and the location of the benches will all influence the time and pattern needed to monitor. Start by following a route or pattern that will cover all areas of the greenhouse. 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. Individual plants should be chosen at random, and inspection should include checking for insects, mites, or disease symptoms.

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 (Figure 26.1). 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.

Sticky Cards

Sticky cards are efficient and important monitoring tools that can alert growers to the early presence of flying insect pests (Figure 26.2). Sticky cards are used to monitor flying pests such as adult whiteflies, thrips, fungus gnats, shore flies, leaf miners, psyllids, winged aphids, and leafhoppers. The cards come in two colors, a bright yellow and a medium blue. The yellow cards attract flying aphids, fungus gnats, whiteflies, leafminers, thrips, and other insects. Blue sticky cards are used primarily to attract thrips. These brightly colored cards are covered with a sticky substance that cards 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.

Sticky Tape

Mass trapping products, such as sticky tapes, are also available for the management of thrips, whiteflies, leafminers, and fungus gnats (Figure 26.2). While sticky cards are primarily used just to alert you to insect infestations, mass trapping tools are used to reduce and manage insect infestations. Mass trapping relies on using enough surface area of the attractive sticky tapes to capture and reduce pest numbers.

Potato Disks

Potato disks are used to monitor for fungus gnat larvae. Cut a fresh potato into disks 1(2.5 cm.) in diameter and ¼–½ (0.6 to 1.2 cm) in thickness; then press the disks into the growing medium in tagged or flagged pots. For plug trays, potatoes may be cut into small “French fry” shapes or wedges and inserted into the growing medium.

Indicator Plants

It is known that some plants are more attractive to pests than others. They can be used as indicator or sentinel plants to detect pests or diseases early. Growers can use them to scout for pests quickly without having to check the whole crop. If the pest is found on an indicator plant, a grower will need to inspect nearby susceptible crop plants to determine if a management action is needed. Some examples of indicator plants are eggplants for whiteflies, marigolds for thrips, sweet peppers for aphids, and petunia for INSV/TSWV.

AI-Driven Insect Detection, Monitoring, and Population Forecasting in Greenhouses

Although conventional pest monitoring methods, such as manual counting on traps and visual inspections, are still widely practiced but are often labor-intensive, prone to human error, and may delay crucial interventions. These limitations can result in unchecked infestations, which increase the need for repeated pesticide applications and compounding costs. Recent advancements in artificial intelligence (AI) offer promising solutions through automated pest detection systems that enhance efficiency and accuracy, providing scalable alternatives for agricultural monitoring.

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