Integrated Pest Management on Organic Farms
Monitoring for Crops Pests
Monitoring (scouting) is a basic component of integrated pest management (IPM) programs. Monitoring is the regular inspection of field crops 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.
The frequency that fields are monitored depends on the type of crop grown, crop stage, and pest(s) present or expected. Field scouting must be scheduled such that increases in pest populations are detected as soon as economic thresholds are reached.
Before a scout enters a field an appropriate route must be planned. For efficiency sake, an M-shaped walking pattern is best used on square or rectangular shaped fields. In irregularly shaped fields scouts must keep in mind that they must cover a representative area of the field. For example, you cannot scout one edge of the field and expect pest populations to be the same in other areas. Do not sample the edge of a field unless it is specifically recommended since pest populations found on the field edge do not indicate what is present in the rest of the field.
Pest Monitoring Techniques
Various pest monitoring techniques are used to monitor pests in the field. 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. 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 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. One good way to do this is adopting a scouting pattern as previously discussed each time you do a visual inspection. Randomly choose plants to inspect along the way. Begin inspection at the bottom of the plant and proceed upwards, from older leaves to younger leaves to new growth. Special attention should be paid to buds, blooms, and any fruit that may be present.
An insect sweep net is useful to estimate pest and beneficial populations (See Figure 11.1). In using a sweep net, develop a uniform sampling technique, which permits comparisons among samples on different dates. Each sweep sample may cover an arc of 180 degree or 90 degree (straight sweep), with the net striking the upper 6 to 8 inches (15 to 20 cm) of the plant. Samples are taken at numerous locations within the field.
A sampling tray is held horizontally just beneath plant foliage, and the foliage above is struck sharply a standard number of times (2 to 5) with a short stick or the other hand. Arthropods falling to the tray are immediately counted and then shaken off. This process is repeated several times around the periphery of the plant.
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 11.2). Pheromone traps are used primarily to lure lepidopteran (moth). 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.
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 11.3). 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.
Black Light Traps
Black light traps also may be useful for trapping insects. The black light trap use ultraviolet light to lure insects into the center of the trap where they drop into a canister. Blacklight traps are often used to determine when nocturnal moths are flying as well as their relative abundance. This information allows pest managers to determine the timing of peak periods of activity and subsequently, pest management activities.
Phenology Calendars and Degree-Day Models
Phenology calendars and degree-day models are knowledge based tools that IPM practitioners can use for monitoring pest development and properly timing control tactics. Both of these tools help account for the annual variability in pest development, which can vary two to three weeks from year to year depending on emergent weather conditions. The life cycle and development of many landscape pests (particularly insects and mites) are highly dependent on the temperature of the surrounding environment. These organisms develop rapidly at warm temperatures and slowly at cool temperatures. As a result, the calendar timing of their development can vary substantially from year to year, making preventive pest control difficult.
A simple method for tracking the seasonal development of pests is a phenology calendar. Phenology is the study of relationships between periodic biological events and seasonal climate changes. Annual natural events such as pest behavior and plant development are often better correlated with seasonal, climate changes than specific calendar dates.
Growing Degree-Day Tracking
This method, referred to as growing degree day (GDD) tracking, involves measuring daily temperatures. For insects, mites, and plants, development is triggered when daily average temperatures rise above a certain base temperature. This base temperature, or developmental threshold, differs depending on the species. As the ambient (air) temperature increases above the threshold, development occurs. The higher the temperature, the faster the rate of development. The most common developmental threshold is 50 degrees F (10°C). This is the temperature at which dormancy is broken in most plants and when many insects become active. But there are a number of insects, particularly those that are active early in the spring, that have a lower threshold (38°F or 43°F, 3°C or 6°C). The base temperature is often noted as a subscript number following the abbreviation for degree day: DD50. Many cool-season vegetables, such as cole crops and peas, have a base temperature of 40 degrees F (4°C).
Unmanned Aerial Vehicles for Pest Monitoring
Unmanned Aerial Vehicles (UAVs) also known as drones are defined as powered aerial vehicles that can fly autonomously or be piloted remotely (See Figure 11.4). Many people refer to UAVs as Unmanned Aerial Systems (UAS), which reflects the complexity of systems onboard these vehicles. UAS include stability and navigation systems, communication and control systems and, if needed, data collection and analysis systems. UAS have either fixed or rotary wings. Rotary wings can be multi-rotor or single rotor (like helicopters).
Geo-referencing and Image Processing
Cameras are the most common sensors to capture plant reflectance for precision agriculture. These payloads can be mounted in a UAS to capture the visual signatures of plant leaves, canopy temperatures and plant reflectance at different spectrums. Geo-referencing cameras play a significant role in processing images taken from UAS, but images taken in flight often require post-processing while tagging a specific photo to the coordinates of precise physical locations.
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