Chapter 11

Insect Pest Management for Organic Crops

Monitoring for Insect Pests and Beneficials

Monitoring for insect pests is an essential part of successful integrated pest management programs. Correct identification of immature and adult stages of both pests and beneficials, and accurate assessment of their presence in the field at various crop stages will ensure appropriate and timely management decisions. Monitoring involves systematically checking crop fields for insect pests and beneficials, at regular intervals and at critical times, to gather information about the crop, insect pests, and natural enemies. If conducted consistently over multiple years, insect monitoring can indicate critical changes in population dynamics and behavior of key insect pests. More frequent checks may be necessary during periods of rapid increase for pests such as spider mites. Some symptoms of insect damage to plants are discoloration or distortion of leaves, blossoms, or twigs; chewing damage; cracked bark; and dieback of plant parts. The appearance of the damage sometimes is enough to identify the insect group that caused it even if the actual insects are not seen. Symptoms of some plant diseases are spots or dead areas on leaves or stems, abnormal growth or coloration, and sudden wilting.

Economic Threshold Level for Insect Control

A decision to use an insecticide should be made only when an insect population has reached or exceeded an economic threshold level (ETL or ET), a fundamental concept in integrated pest management. The ETL of a pest population is the level at which control is needed to prevent economic loss (i.e., the projected cost of damage is greater than the cost of control). The amount of pest presence or damage that can be tolerated is determined by many factors, including the type of pest and damage, crop species and cultivar, stage of plant development, time until harvest or sale, and market conditions.

Insect Pest Monitoring Methods

Monitoring for insects is an essential part of successful integrated pest management programs. Correct identification of immature and adult stages of both pests and beneficials, and accurate assessment of their presence in the field at various crop stages will ensure appropriate and timely management decisions. Good monitoring procedure involves not just a knowledge of and the ability to identify the insects present, but also good sampling and recording techniques.

Filed Observation

Field observation can be useful to determine pests and beneficial insect populations. Plant diseases, environmental disorders, and improper cultural practices can also be observed visually. Field observations should be done by the same person throughout the season. That means regularly checking plants in a number of different areas of your farm.

Sweep Nets

In most agricultural situations, an insect sweep net is useful to estimate pest and beneficial populations. In using a sweep net, develop a uniform sampling technique. This 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.

Trapping

Pheromone Traps. Traps baited with sex pheromones, the chemicals usually emitted by female insects to attract males of the same species for mating, have become a valuable tool for monitoring pest populations in survey and integrated pest management (IPM) programs. 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. Sticky traps are glue-based traps frequently used in insect pest control to catch and monitor insects and other pests. 

Sweep Nets. Small insects are best monitored with a sweep net, particularly if there is a large area to cover. From a practical standpoint, sweep net sampling works best on low-growing crops like carrots, peas, and leafy greens.

Recordkeeping

Good recordkeeping is important in insect pest management because it helps growers remember if particular conditions, practices, crops, or crop varieties were prone to damage by insects, mites, or another pest species. Good records can also help growers know what pest and beneficial organisms they can expect on particular crops on the farm at different times of the year.

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