Chapter 11

Insect Pest Management for Organic Crops

Cultural Control of Insect Pests

Cultural control practices are usually multipurpose technical procedures that create environments that either avoid high-risk situations for infestations or develop unfavorable conditions for insect pests. Cultural practices are often the foundation of preventive control strategies in integrated pest management (IPM) programs. Cultural controls are not usually intended to suppress insect outbreaks, but are designed to discourage the introduction, establishment and development of insect pest populations. When using cultural control techniques, it is important to be aware of the environmental context of the field. Production efficiency, yields, soil conservation, natural enemy habitat need to be taken into account for each crop/pest complex, climate, and surrounding environment. This is because cultural control techniques that maximize insect control may at times be impractical in particular contexts. For instance, the practice of tilling to disrupt an underground life stage of an insect pest may not be practical for a no-till farmer trying to reduce erosion in the field. Cultural control practices are most effective when the target insect pests have few suitable host plants, do not disperse far or frequently, and/or have complex nutritional or environmental requirements during their life cycle.

Host Plant Resistance to Insect Pests

One of the mainstays of integrated pest management is the use of crop varieties that are resistant or tolerant to insect pests. A resistant variety may be less preferred by the insect pest, adversely affect its normal development and survival, or the plant may tolerate the damage without an economic loss in yield or quality.

Effects of Tillage on Insect Pest Management

Tillage can disturb insect pests by killing them, by destroying the residue that the insects rely on for shelter and food, or by physically disturbing the soil habitat. Tillage typically disturbs insects at their most vulnerable stage, exposing grubs and adults to the harsh environment of the atmosphere where they may freeze, overheat, or desiccate or be eaten by birds.

Adjust Crop Planting to Disrupt Pest Habitat

Crop planting can be adjusted both in space and time to reduce the development of large pest populations.

Planting Dates

Planting during optimum growing conditions ensures rapid seedling emergence and subsequent growth. This reduces the amount of time that plants are susceptible to injury from seedling insect pests. For some insect pests, planting a crop early so that it reaches a less susceptible physiological stage can be a practical solution in minimizing the impact of harmful insect pests. to a pest problem. For example, corn earworm causes fewer problems in early-planted sweet corn than late-season corn planting.

Harvest Dates

In the Southeastern United States, spring plantings of watermelon that are harvested by early July often escape the period of time that certain insect pests pose their greatest economic threat. Harvest date can be an important factor in managing the alfalfa weevil too.

Spacing and Seeding Rates for Controlling Insect Pests

Crop row spacing can have a definite impact on insect problems. For example, it has long been realized that soybean fields, which do not reach canopy closure by bloom are more susceptible to damage by the corn earworm.

Managing Soil Fertility to Minimize Insect Pests

Proponents of organic farming have long promoted the view that the likelihood of pest outbreaks is reduced with organic farming practices, including establishment and maintenance of “healthy” soil.

Effects of Too Much Nitrogen

Healthy, vigorous plants that grow quickly are better able to withstand insect pest damage. However, over-fertilizing crops can actually increase insect pest problems. Research has shown that increasing soluble nitrogen levels in plants can decrease their resistance to pests, resulting in higher pest density and crop damage. For example, increased nitrogen fertilizer rates have been associated with large increases in numbers of aphids and mites.

Managing Irrigation to Control Insect Pests

Poor water management (especially too little water) can predispose plants to certain pests such as spider mites. Because irrigation methods vary considerably (whether drip, overhead sprinkler, or flood irrigation), the impact of irrigation on insects can vary. Pest insect populations can increase if irrigated plants are lusher and more attractive than surrounding plants. Likewise, plants stressed by drought can be more attractive to insect pests or less tolerant to their feeding.

Sanitation in Controlling Insect Pests

Sanitation prevents or reduces insect pest infestations through removal of breeding or hibernating sites. For example, newly hatched grape cane borer larvae can be controlled by keeping plants healthy and by removing any dead or dying portions. Prunings should be collected and burned before bud-break in the spring in order to eliminate overwintering larvae before they pupate. Collecting dropped fruit from beneath an apple tree reduces the next season's population of apple maggots (Rhagoletis pomonella), codling moths (Cydia pomonella), and plum curculio (Conotrachelus nenuphar).

Managing Insect Pests through Farm Biodiversity

Biodiversity offers great potential for managing insect pests. Diverse plantings often decrease insect pest populations. Insect pests are more likely to find and remain on pure crop stands where food sources are concentrated. Fields containing a variety of crops are often rich in above- and below-ground beneficial organisms that naturally control insects, inhibit growth of disease organisms, boost a crop’s natural defenses and suppress some weeds. The use of crop diversity, crop rotations, scattered fields, adjacent uncultivated land and a perennial crop component are methods that can be used to reduce pest pressure.

Management of Insect Pests with Crop Rotations

Crop rotation, as described in section § 205.205 of the National Organic Standards, is fundamental to good organic management and serves several functions in addition to providing insect pest management including maintenance or improvement of soil organic matter content, management of plant nutrients, and erosion control. The effectiveness of crop rotation as a tool for insect pest management depends on the life cycle of the target insect.

Management of Insect Pests with Intercropping

Intercropping is the planting of more than one crop in close proximity as part of the same farming system. The design of intercropping system can vary dramatically depending on the purpose of the intercrop for the farming operation. Intercropping produces the benefits of on-farm diversity, increased productivity, resource distribution balance, farm risk reduction, and weed and insect pest control.

Management of Insect Pests with Cover Cropping

Cover crops not only are important in slowing erosion, improving soil structure, and providing soil fertility but play an increasingly important role in managing insect pests. Ecologists tell us that stable natural systems are typically diverse, containing many different types of plants, insects, mammals, birds, and microorganisms. Growing cover crops adds diversity to a cropping system. Cover crops may harbor insect pests that could be harmful to the cash crop. Before planting a cover crop, be sure to investigate specific pest/crop interactions that may become a problem. Understanding these interactions and the conditions that favor them helps make good management decisions.

Management of Insect Pests with Genotypic Diversity

While growing crop varieties that are resistant or tolerant to insect pests can be a valuable tool as a cultural control measure, genotypic diversity within a crop species can provide similar value. Most row crop fields in the United States are planted with a single crop variety, but planting different crop genotypes within the same field can have pest management and agronomic value. For example, it is common in Europe and Asia for farmers to mix together seeds of five or so varieties (e.g., especially wheat, barley, and rice) and plant this “cultivar mixture” in their fields

Insectary Plantings for Management of Insect Pests

Insectary plantings are plants that provide resources such as nectar and pollen to beneficial insects. Growers incorporate insectary plantings into fields with the aim of enhancing the insect pest suppression activity of natural enemies. To the extent that these food resources lead to more beneficial insects around farms, insectary plantings may result in greater biological insect pest control. Insectary plantings that contain a variety of plants with different flowering periods providing a year-round food supply for beneficial insects. Insectary plantings that contain species that flower at different times extends the potential time the floral resources are available.

Insectary Plants

There are many plant species, which attract beneficial insects. They include but are not limited to the following families, Apiaceae (formerly known as Umbelliferae), Asteraceae (Compositae), Lamiaceae, Fabaceae, and Brassicaceae, which are discussed in more detail below.

Selecting Insectary Plants

When selecting species to plant, keep in mind that the main aim is to produce an abundance of different blooms for as much of the growing season as possible. Ideally, the species selected should be cheap, readily available, easy to grow, and quick to bloom.

Timing of Insectary Plantings

Timing is as important with insectary plantings because many beneficial insects are active only as adults and only for discrete periods during the growing season and need pollen and nectar during those active times. Buckwheat (Fagopayum esculentum) and mustard are early blooming plants, but their flowering period is short.

Types of Insectary Plantings

Many approaches to integrate cover cropping with cash crop production have already been practiced. These include planting cover crops as 1) insectary plantings within the current crop field or orchard; 2) insectary plantings outside of the crop field or orchard; 3) insectary plantings in cover crops; and 4) insectary planting in selectively managed weed patches.

Management of Insect Pests with Trap Crops

Trap crops are grown as a control measure to lure insect pests away from the cash crop to protect it from attack by providing insect pests an alternative site for feeding and oviposition. Insect pests are either prevented from reaching the crop or concentrated in certain parts of the field away from the main crop. The principle of trap cropping relies on pest preference for certain plant species, cultivars, or a certain stage of crop development. Plants produce chemicals, or volatiles, that attract insects for pollination and repel insect pests.

Design and Arrangment of Trap Crops

Trap crops can be arranged in various spatial patterns and the choice of design will depend on target pest, pest pressures, and farm size. Extremely mobile insects such as cucumber beetles are more difficult to manage with trap cropping than the slow moving insects, e.g., Colorado potato beetle. Some of the spatial arrangements include: perimeter trap cropping, row trap cropping, and strip trap cropping. Perimeter trap cropping is most popular trap cropping arrangement used by farmers. Perimeter trap crops can be planted on all four sides of the main crop in sufficient density (e.g., usually at least two rows) in order to provide a physical barrier to mobile insects.

Management Strategies for Trap Crops

Insect pests in the trap crop must be managed so they don’t eventually disperse into the fields and damage the cash crop. Conventional growers can use insecticide sprays on the trap crops but that’s not an option for organic growers.

Examples of Trap Cropping

Perimeter trap cropping has been shown to be effective at controlling diamondback moth larvae on cabbage, using collards as the trap crop; pepper maggots on bell peppers or eggplant, using hot cherry peppers as the trap crop; and cucumber beetles on summer squash, winter squash, cucumbers, melons, and sometimes pumpkins, using Blue Hubbard squash or another variety as the trap crop.

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