Module 3: Tools, Methods, and Tactics of IPM

By this stage of the course you have a good idea of what IPM and have looked into some of the fundamental concepts underlying this approach to pest management. In this module we would like to introduce some of the major tools that are used in IPM. Modern agricultural science as well as indigenous farmer knowledge acquired over thousands of years provide us with a comprehensive "toolbox" of pest control methods and an agricultural professional needs to have a good understanding of what they are, how they work and the advantages and disadvantages associated with each.

While the list of such tools is quite long, all IPM methods can be classified into 3 main categories:

1. Prevention.
2. Intervention.
3. Regulation.

On the following pages we will look into each of these approaches and tools in more detail.

3.1: Prevention

Preventing the occurrence of pest problems before they can cause economic damage is by far the most preferred approach in IPM and the key to prevention is crop health. The first rule of IPM is often cited as "grow a healthy crop". Pest problems in agricultural crops are often linked to inadequate plant health and can be avoided through good farming practices. Pests prefer sick, weak, or injured plants, and good crop health is therefore related to a lower incidence of pest problems. Preventative measures in IPM often address pest problems indirectly by improving crop health.

Some preventative measures directly inhibit pest problems. They are proactive and are implemented before there are any pest problems. Some of these direct preventative measures target specific pests while others reduce the chance of pest outbreaks generally.

Many preventative measures act by reducing the carrying capacity of the agroecosystem for a particular pest. This can be achieved through increased natural enemy populations, decreased shelter or nest sites, decreased food, or fragmentation of the agroecosystem. A key and very effective preventative method is to increase the biodiversity of the agroecosystem.

3.1.1: Biodiversity

Increasing the biodiversity of the agroecosystem will increase system stability and reduce pest outbreaks. By encouraging many different species to co-exist in an agroecosystem, the farmer can reduce the risk that any one of them will become a major pest problem.

Biodiversity can be encouraged in many different ways. Increasing soil organic matter, mulching exposed soils, and reducing unnecessary cultivation can increase soil biodiversity. Plant biodiversity can be increased by encouraging hedgerows, interplanting crops, using living mulches, and planting trees. Animal biodiversity can be increased by integrating livestock into the agroecosystem, protecting natural enemy habitat, adding ponds, and increasing plant species diversity. Finally, crop genetic diversity can be increased by planting multiple cultivars of a single crop, or by using older varieties and landraces.

3.1.2: Good Agronomic Practices

Good agronomic practices can prevent pest problems because they encourage good crop health and bolster crop resistance to pests.

Crops should be grown in the appropriate climate and in the appropriate season. Crops grown out of season, outside their ideal range or planted too close together are often stressed and therefore more prone to pests. Crop rotations, pest-resistant varieties, good sanitation, removal of alternate pest hosts, and disease-free stock and seeds can all be used to break persistent pest cycles. Appropriate fertilization and irrigation results in healthy, pest-resistant crops.

Some specific preventative agronomic practices are detailed on the following pages. These are:

1. Spatial methods
2. Sequence-related methods
3. Planting materials and iinputs

3.1.3: Spatial Methods of Prevention

The way that crops are arranged on a farm can affect their susceptibility to pest outbreaks. Several methods that can prevent pest problems are listed below. You may also click on each method to view supplementary information about that method.

• Cropping Pattern. Many pests have multiple alternative hosts. By avoiding planting alternative hosts near each other, pest buildup can be avoided. Alternatively, planting a crop that attracts or encourages beneficials of neighbouring crops should be considered.

Cropping Pattern: The pattern of crop plants in an agroecosystem can increase or decrease pest problems. Many pests have multiple alternative hosts, and these should not be planted near each other. For example, the cotton stainer bug, Dysdercus, uses volunteer cotton and Malvaceous weeds as an alternate host. It is probably wise not to grow Malvaceous crops such as okra (Abelmoschus esculentus) or roselle (Hibiscus sabdariffa) near a cotton crop.

On the other hand, many natural enemies are attracted to multiple hosts and planting crops with the aim of increasing natural enemy populations should be considered. For example, cilantro (Coriandrum sativa) and buckwheat were found to attract hoverflies into neighbouring broccoli, while mustard (Brassica juncea) and buckwheat attracted parasitic wasps into the broccoli crop. (see - Enhancing Biological Control with Beneficial Insectary Plants). Traditional cropping patterns are often called "companion planting". Although little scientific research has been conducted on the exact mechanisms of companion planting, these combinations have often been developed through extensive trial and error and are worth considering. For more information on companion planting, see Companion Planting - Basic Concepts & Resources from Appropriate Technology Transfer for Rural Areas (ATTRA).

• Plant Spacing. The space between plants affects air flow and sunlight penetration, and therefore moisture and humidity levels. Wider spacing often results in reduced fungal disease, although close spacing tends to repel aphids and thrips.

Plant Spacing: The distance between plants in a field effects air circulation and light penetration below the crop canopy, potentially altering the understory microclimate. By optimizing crop spacing, pest problems can be reduced and yield increased.

Close plant spacing reduces the area of 'bare ground' exposed in a crop as well as reducing the length of time it is exposed. In some crops, canopy establishment is important for suppressing weeds, and colonization by aphids, thrips, and other passively dispersing insects is reduced. Reduced virus incidence in closely-spaced plants has also been reported. High density plantings also allow for some plant losses to pests before harvest - undamaged neighbours of damaged plants will compensate yield due to the removal of interplant competition. Crops prone to seedling pests are particularly suited to higher than optimum seeding rates. Rice is an example of a crop that can suffer extensive seedling damage yet return a good yield through compensatory tillering of surviving plants.

Wide plant spacing allows more air circulation and sunlight penetration within the crop, reducing understory moisture levels. Generally, this helps reduce fungal disease, although soil splash from 'bare ground' during rainfall and irrigation can increase soil-borne disease transmission. Wide spacing also facilitates weeding. Sowing at lower than the agronomically optimum density can result in a yield penalty, although this is justified if the value of the averted pest damage is greater than the value of sacrificed yield. For an example of wide-spacing in rice, see this article about the SRI Method.

• Intercropping. Growing two or more crops in the same, alternate, or double-rows often results in reduced pest problems. Carefully chosen intercrops can disrupt visual and odour cues that pests use to locate crop plants, physically limit dispersion, and enhance natural enemies.

Intercropping: The planting of intercrops can reduce pest problems by disrupting visual and odour cues, physically limiting dispersion, and enhancing natural enemies. Mixed intercropping occurs where crops are intermingled in a field, while row intercropping refers to mixed crops arranged in rows. Intercropping is widely used in traditional farming systems as a way to assure an adequate harvest. As a consequence, most of the food in tropical Asia is produced using some form of intercrop. In good years, intercrops can produce more food than monocrops on a given piece of land.

Intercrops must be carefully chosen to be effective, however. When similar crops with similar pests are intercropped, pest problems are just as likely to increase. Choosing crops with different growth forms and pest regimes is the best way to take advantage of intercropping's benefits. Mixes of short and tall annuals (e.g. sorghum with cowpeas, maize with beans) are commonly found intercrops in the tropics. Sometimes a third crop, such as a cucurbit, is grown as well. Intercrops can also be used to grow several varieties of a single crop. Resistant varieties of a crop can protect high-value but susceptible varieties when they are intercropped.

• Strip Cropping. Growing two or more crops in broad, alternating strips has many of the benefits of intercropping but allows a broader range of mechanized field operations.

Strip Cropping: Strip cropping is a compromise that takes advantage of the pest management benefits of intercropping, but permits field operations normally associated with monocropping. Crops are planted in broad strips, either on purpose, or because inheritance traditions have resulted in long, narrow fields.

Crops used in strip cropping systems must not be alternate hosts for each other's major pests. Also, because strip cropping effectively increases the amount of 'edge' in a crop, crops that suffer from edge-favouring pests (such as grasshoppers) should be avoided.

Strips do not have to be alternating or divided evenly between two crops. A strip of crop A in a field of crop B can act as a barrier to pests, or as a harvestable hedgerow.

3.1.4: Sequence-related Methods of Prevention

Previous crops can have an effect on pest problems in the present crop. Planting crops in a particular sequence can reduce pest problems in general and soil-borne pest problems in particular. Several sequence-related planting methods that can prevent pest problems are listed below. You may also click on each method to view supplementary information about that method.

• Crop Rotation. Shifting crops from field to field over several seasons can reduce or prevent the buildup of pests, especially non-mobile or soil-borne varieties. For mobile species however, crop rotation often serves only to reduce or delay outbreaks.

Crop Rotation: Crop rotations have long been used by farmers both as a fertility and pest management tool. Planting a succession of different crops in a field over several years prevents the buildup of pests that can occur when the same crop is grown repeatedly. Crop rotations are particularly effective at controlling soil-borne diseases, as well as soil-dwelling organisms that do not disperse well.

Crop rotations work best when the crops in the rotation have few shared pests. A common rotation in temperate areas is maize, wheat, and red clover. Of the 50 or more serious pests that attack these crops, only 3 are important pests of all three crops. Crops with few pests, such as garlic, are often grown in a rotation to break pest cycles.

Some crops directly reduce pest problems for the succeeding crop. African marigolds release an anti-nematodal compound called thiopene, which can reduce nematode loads for subsequent horticultural crops. Cucurbits or sweet potato are often included in a rotation because they tend to choke out persistent weeds.

• Multiple Cropping. Growing several consecutive crops in the same field in a single year can addresses pest problems on an annual basis. Often, the cultural requirements of the second or third crop also indirectly address pest problems.

Multiple Cropping: Multiple cropping, or multicropping, is a cropping system in which several crops are grown in succession within a season. Often the same multicropping scheme is followed year after year. Multicropping is more common where there is distinct seasonality, such as in temperate or monsoonal areas.

The crops grown in a multicropping scheme are often limited by climate or pests. In many tropical countries, wet-rice is grown during the rainy season, followed by cool-season vegetables such as cabbage. If sufficient irrigation or soil water is available, a third, drought-tolerant crop may be grown (e.g. legumes).

Many farmers grow a cereal crop immediately before higher-value crops such as tobacco, cotton, or vegetables. Multicropping a monocotyledonous crop with a dicotyledonous crop effectively disrupts soil borne pests. It also improves weed management, as the persistent monocot weeds of cereals can be easily identified in a dicot crop and vice versa.

• Overseeding and Undersowing. Planting or seeding a second crop into an established crop can reduce pest problems.

Overseeding and Undersowing: Overseeding and undersowing are farming techniques where one crop is sown into another. Other terms for this operation include relay intercropping, and interplanting.

There are many good reasons to overseed. Overseeded crops can increase yields in a season, reduce erosion and improve weed control, depending on the crops involved. However, overseeding can also increase pest management requirements if crops are chosen for criteria other than their IPM compatibility. See Two Crops in One Year for example. Overseeding with IPM principles in mind can be very successful. Brassicas are often undersown with clover to reduce cabbage root fly infestations. In Georgia, USA, farmers who planted cotton into strip-killed crimson clover reduced reduced their use of insecticides and nitrogen fertilizer (see Intercropping Principles and Practices).

Orchards and plantations are often undersown with annuals, herbs, and other plants with the aim of reducing pest problems. Flowering herbs are commonly used as cover crops in grapes and apple orchards. Traditional shade-grown coffee is interplanted with native shade trees, increasing biodiversity and reducing pest problems.

3.1.5: Planting Materials and Inputs

Both the genetic make-up and the health of planting materials can affect crop susceptibility to pest problems. Several preventative measures related to planting materials are listed below. You may also click on each method to view supplementary information about that method.

• Host-plant resistance. Crop plants that are bred to resist certain pests are an important component of IPM. Many diseases and insects have been managed effectively by breeding genetic resistance into modern varieties. The mechanisms of host-plant resistance are diverse, and varieties with resistances to multiple pests have been developed. Biotechnology - in particular the controversial approach of genetic engineering - presents many interesting possibilities for future resistant varieties as well as concerns about its safety.

Host-Plant Resistance: Crop varieties that are bred to resist certain pests are an important component of IPM. Such varieties tend to reduce pesticide use, require little change in farming practices, and are seen as the easiest way to pass high-level research results directly to farmers. Host-plant resistance is most effective when integrated with other techniques, however. Massive plantings of resistant varieties can cause pests to become 'resistant to the resistance', forcing plant breeders to breed new varieties to replace old, ineffective ones.

Crop plants can resist pests in three main ways.

• Nonpreference. The crop plants are avoided by the pest because they do not 'like' it.
• Antibiosis. Plants cause a reduction in the biological performance of the pest.
• Tolerance. Plants can tolerate the pest and still provide an adequate yield.

The mechanisms of resistance are diverse. Crops resist pests through color, palatability, hairiness, waxy coatings, gross morphology, gumminess, necrosis, hardness, phenological shifts, toxin production, nutrition, integration with biological control, and compensation. Each mechanism of resistance may be classified under one of the three main types above.

Many resistant varieties have lost their resistance through mass plantings and adaptation of pest populations. Resistance management plans are designed to reduce or prevent the development of resistance, by planting resistant varieties in a particular way. For example, many maize growers will grow a strip of an older, susceptible variety around a new resistant variety so that the pest has something preferrable to eat and will maintain its current resistance status.

• Disease-Free Plants and Seeds. Many pests are transmitted along with seeds and other planting materials. Disease-free stock and seeds can prevent many endemic pest problems, particularly in vegetatively-propagated plants.

Disease-Free Plants and Seeds: Many pest problems are borne on planting stock or seeds. Virus and disease loads on vegetatively propagated stock can reduce yields by as much as 50%. Farmers can greatly improve plant health by starting with clean planting materials.

Many countries have certification programs for seed and planting stock. Certified seed is often more expensive than locally available seed but the extra cost should be balanced against the potential risks of using uncertified seed. Vegetatively propagated crops are often grown in tissue culture to obtain disease-free strains.

Some planting materials can be sterilized by the farmer himself. INIBAP has outlined a method for preventing banana disease by using a hot water bath on planting stock. Insect pests can be removed from seed stock by dry heating in an oven. Sunlight, carbon dioxide, steam, and bleach solutions are other low-tech ways to reduce transmission of pest problems through planting stock.

• Crop genetic diversity. Crop varieties with different host-plant resistances can be intercropped in ways that augment these characters. High crop genetic diversity is a traditional way of ensuring an adequate harvest.

Crop Genetic Diversity: Historically, farmers altered the genetic makeup of crop plants by selecting propogating plants with desirable characteristics. As scientists began to understand how crop genetics worked and became more adept at manipulating the genetics of a crop, the genetic diversity of major crop varieties were reduced in order to produce uniform high yields. This trend towards reduced crop genetic diversity has continued with the advent of biotechnology techniques such as marker-aided selection and genetic engineering.

Reducing crop genetic diversity may lead to a uniform crop with desirable characteristics, but it also leaves crops vulnerable to pests and adverse environmental conditions. Often, as in the case of hybrids, the crop is restricted to a single genome. The consequences of massive plantings of single-genome hybrids can be severe, as was the case in the United States in 1970-71 when southern corn leaf blight destroyed 15% of the US corn crop due to broad plantings of a susceptible hybrid. Similarly, massive plantings of pest-resistant rice varieties in Asia have led to widely-distributed resistant pests after a few seasons, and subsequent pest problems as pests develop 'resistance to the resistance'.

There are several ways in which crop genetic diversity can be increased and genetic vulnerability decreased.

• Promotion of traditional varieties. Traditional varieties that are mass selected tend to have high degrees of genetic diversity. Although these varieties tend to be lower-yielding than modern, high-yielding varieties, they are more dependable and stable under flucutating pest regimes.
• Intercropping multiple varieties. Intercropping multiple varieties of a single crop can increase crop resistance to pests, especially when the varieties are resistant to different pests. For example, the intercropping of a blight-resistant rice cultivar with a blight-susceptible cultivar of rice allowed the blight-susceptible cultivar to be grown successfully in an infested area.

On-site selection and seed saving. By selecting and propagating crop varieties on farm, farmers can adapt a variety to their local conditions while maintaining crop genetic diversity.

• Plant Appropriate Crops and Cultivars. Most crops and cultivars are adapted or bred to perform best under particular environmental conditions. Crops grown outside of this optimum location are often subject to increased stress and reduced health, and are prone to pest problems. Growing the right crop in the right location and season is a sensible pest prevention method.

Plant Appropriate Crops and Cultivars: Most crops grow best under certain environmental conditions. When these crops are grown at the limits of their range, they often suffer from more pest problems. For example, the grape (Vitis vinifera) is a temperate to sub-tropical crop that is also cultivated in the tropics. In Thailand, commercial grape vines may be treated 2 or 3 times per week with copper and sulfur fungicides in order to control various fungal diseases. While temperate grape crops are also often heavily sprayed, this excessive requirement for fungicides can be considered the result of growing a crop well outside of its optimum range.

Wheat is another example of a crop that is limited to certain environmental conditions. While it can physiologically survive in hot, humid conditions, diseases and pests are encouraged by such conditions and effectively limit its cultivation in the tropics. Wheat consumption is increasing rapidly in many tropical countries, but breeders have been unable to develop wheat strains which are suitable for tropical conditions. Growing wheat in the tropics therefore requires heavy use of pesticides, and an IPM-oriented farmer is probably better off choosing another crop.

Tomatoes are a widely grown cash-crop throughout the world. In the tropics, they are grown mainly in the dry season, partially because tomato plants need temperatures below 30 degrees Celsius in order to set fruit, and partially because of pest pressure. Fresh tomatoes can be sold at a premium in the wet season, however, and many farmers attempt to grow them during this more difficult 'off-season'. Special cultivars have been developed for this purpose, and these should be chosen over the 'regular' varieties for wet season growing. By growing cultivars adapted to each season, an IPM farmer can effectively reduce potential pest problems. Tomatoes are a good example of a crop where different cultivars are more appropriate for different seasons in the tropics - see Suggested Cultural Practices for Tomato, a publication from the Asian Vegetable Research and Development Center (AVRDC).

Optimizing inputs to crops produces results in healthy plants that resist pests. Fertilization and irrigation are discussed here in the context of pest problem prevention.

• Fertilization. Proper plant nutrition plays an important role in IPM. Over-fertilized plants often suffer pest outbreaks due to 'soft' or watery growth, while under-fertilized plants are subject to stress-related pests. Certain micronutrients can play important roles in pest prevention, especially in the case of plant disease.

Fertilization: Fertilization and manuring indirectly reduce pest problems by contributing to healthy plants. Fertility management can also be used directly to control weeds and plant diseases.

Soils with adequate, balanced fertility result in quick-growing, healthy plants that resist pests. Fast-growing plants reduce opportunities for pests that attack certain growth stages, such as stem-borers, by shortening their period of vulnerability. Fast-growing plants can also compensate for damage that does occur. Fast-growing plants quickly form a canopy, discouraging pests that disperse aerially or seek bare ground.

Although high fertility can increase potential yields, balanced fertility that is appropriate to the intended crop is the key to pest prevention. Many diseases and insect pests are associated with too much nitrogen fertilizer in proportion to phosphorous, potassium, and other elements. Similarly, several pest problems have been managed using a disproportion of specific trace elements, such as silicon or zinc.

Building balanced soils through the addition of compost and organic matter can help reduce nutrient imbalances. Relying on non-chemical sources for at least part of a crop's fertility requirements can indirectly reduce pest problems.

• Irrigation. Overwatering and drought can stress crop plants. Water management in agroecosystems can also have large effects on pest habitat and populations. Water to ensure adequate supplies to the crop, keeping in mind the positive and/or negative effects that irrigation has on pest and beneficial population

Irrigation: Carefully managed irrigation can be an excellent way to manage pests. First, applying an optimum amount of water to a crop results in quick-growing, healthy, and pest-resistant plants. Overwatering can cause plants to become lush and prone to fungal diseases and insect such as thrips and aphids. Plants stressed from underwatering wil be less able to withstand pest attacks.

Second, water can be used directly on pests. Strong jets of water can physically knock pests off of plants, flooding a field can drown non-aquatic pests, and newly-irrigated soil particles may swell enough to crush soil-dwelling pests.

Third, water can be used indirectly to control pests. Flooded rice-paddies attract fish, frogs, and other aquatic predators to prey on pests. Raising and lowering water levels in a flooded field can augment predation of above-water pests by aquatic predators. Adjusting irrigation can speed or slow crop maturity, preventing a crop from ripening at the same time as a pest population peak.

3.2: Intervention

Unfortunately, it is not always possible to totally prevent pests from damaging a crop or reducing its economic value. This means that when pest populations do begin to approach the Economic Injury Level an intervention has to be made to protect the crop and farm profits.

Fortunately, once a decision has been made that an intervention is required, a range of intervention options are available. These include chemical, biological, cultural, physical and genetic interventions. The following pages describe the various intervention tools methods at the disposal of an IPM practitioner.

Please note that many of these intervention methods have also been listed as preventative measures in the previous lessons. While technically an intervention is reactive to a pest problem and a preventative measure is proactive, in practice the distinction between preventative measures and interventions is often blurred. For example, using a pest-resistant cultivar as a preventative measure in one season could be a reaction to a specific pest problem in previous crop.

3.2.1: Chemical Interventions

Chemical interventions introduce organic and inorganic substances into the agroecosystem to manage pest problems. They can be man-made (synthetic), collected and derived from organisms (biopesticides, pheromones, allelochemicals, insect growth regulators) or collected from other natural sources (inorganics).

Chemical interventions can be applied in a variety of ways. They may be diluted in water or oil for spraying, left dry for application as dusts or granules, or added to baits or traps. Spraying, dusting, fogging, smoking, and other techniques can be used to apply chemical interventions to crops.

For a summary of chemical intervention formulations, visit the University of Nebraska-Lincoln's Pesticide Education Resources chapter on formulations. The FAO Pesticide Management Unit and US EPA Office for Pesticide Programs have additional information and links about chemical interventions.

Categories of chemical interventions include the following. You may click on each method to view supplementary information about that method.

• Synthetic pesticides. These include some of the most notorious and also the most useful of all plant protection products.

Synthetic Pesticides: Synthetic pesticides are made from carbon-containing compounds and are widely used and available throughout most of the world. Synthetic pesticides are often classified according to their chemical makeup, their intended target pests (insecticides, fungicides, etc.), or their mode of action. For further information about different classes of synthetic pesticides, follow the links below.

As noted in Module 1, synthetic pesticides have advantages and disadvantages that must be considered before they are used in an IPM program. Synthetic pesticides can be very effective in the short term, but often cause problems such as pesticide resistance, pest resurgence, or pest replacement in the long term. In addition, social, health, economic, and political costs must always be considered.

Many IPM programs are based largely on the use of synthetic pesticides. IPM practitioners need to calculate economic injury levels and make recommendations, and using synthetic pesticides is often simpler and more predictable than other IPM interventions. However, every effort should be made to integrate other interventions into IPM programs in order to reduce potential harmful effects from synthetic pesticide use. A program which makes limited, intelligent use of synthetic pesticides is often more effective than one that relies entirely on synthetic pesticides for crop protection, or abandons synthetic pesticides suddenly and completely.

Synthetic pesticides can be used effectively to complement other IPM methods, such as biological control. Using a synthetic pesticide that selectively kills pests will increase the proportion of beneficials to pests, possibly increasing the efficiency of biological control. Understanding the biology and lifecycles of both pests and beneficials is crucial to using synthetic pesticides effectively in IPM.

For more information about synthetic pesticides, go to the following links.

Two chapters in Radcliffe's World IPM Textbook overview the chemistry of synthetic pesticides. One deals with insecticides, the other, herbicides.

CropLife Asia provides a regional perspective from the plant science industry.

The Compendium of Pesticide Common Names is useful for identifying synthetic pesticides.

The British Crop Protection Council publishes The Pesticide Manual, which is a standard reference for anyone working with synthetic pesticides.

• Botanicals. Chemicals derived or refined from plants.

Botanicals: Botanicals are pesticidal substances derived or refined from plants. While most biopesticides are produced on a small or local scale, there is an increasing demand for commercially-produced biopesticide formulations where the amount and strength of the active ingredient is known. Neem (Azadirachta indica) and pyrethrum (Chrysanthemum cinerariaefolium) are commonly used commercial botanicals. Garlic and hot peppers are used on a non-commercial basis by many farmers and gardeners.

Most botanicals are little-studied and therefore not widely accepted, especially by commercial farmers. The extraction, processing and formulation of many botanicals are known only at a local level and are produced and used mainly by small farmers. Rather than adopt a widespread botanical such as neem into an IPM program, IPM practitioners should evaluate indigenous botanicals for inclusion in an IPM program.

To see some innovative botanicals, visit the Soil Technologies Corp. Pest Control page.

• Inorganic pesticides. Chemicals such as sulphur, chemical mixtures such as Bordeaux mixture, and mineral products such as diatomaceous earth are included in this category.

Inorganic Pesticides: Inorganic pesticides are substances derived or refined from non-living natural sources. They are termed 'inorganic' because they do not contain carbon compounds. Many of them contain heavy metals which are persistent and toxic to humans. Inorganic pesticides that were used in the past but are seldom used today container arsenic, cyanide, and mercury. In general, inorganic compounds are little used in modern agriculture.

The exceptions to this rule are copper and sulphur-based compounds which are used as fungicides. Sulphur is a widely used and safe way to control fungal diseases and mites. Bordeaux mixture, a combination of sulphur, copper, and lime, is an important fungicide used in orchards.

• Semiochemicals. Chemical cues emitted by organisms that modify the behaviour of other organisms.

Semiochemicals: Semiochemicals are chemicals produced by organisms that modify the behaviour of animals. The most important types of semiochemicals for IPM are pheromones and allomones. Pheromones are emitted by members of a species to modify the behaviours of other members of that species. Allomones are like pheromones, except they are emitted by one species in order to modify the behaviour of another species.

The most commonly used pheromones in agriculture are sex attractants. These chemicals are produced by females to attract males for mating and are used by IPM practitioners to attract males into traps. Pheromone traps are often used to determine population density by sampling the numebr of males caught in a trap in a certain amount of time. Alarm pheromones can be used to repel certain species from crops. A traditional practice in Mexico takes advantage of the alarm pheromones released by burning beetles. Placing burned beetle pests in bean fields overnight effectively repels living beetle pests by the next morning.

Allomones are produced by many plants to repel herbivores and prevent them from feeding. Many secondary-products of plants, such as tannins, cyaninis, etc. - are in fact anti-herbivore allomones. Some act by repelling, others directly effecting the growth and development of the pest organism. Allomones have not been used very much as an applied intervention, but they are often the basis for companion planting and other cultural interventions.

• Hormones. Chemicals that interfere with the normal growth and development of animal pests.

Hormones: Hormones are chemicals produced in one part of a pest's body that effect the growth and behaviour of other parts of the body. The most successful hormones used in IPM are insect growth regulators. These hormones affect the development of juvenile insects, either causing death or abnormality in newly hatched insects, or preventing sexual maturity.

Insect growth regulators are usually synthetic versions of naturally-occuring hormones. They are highly selective and have extremely low toxicity to other organisms (including humans). However they are expensive, difficult to apply and use, and their extreme specificity limits their distribution and usefulness, especially in the developing world.

3.2.2: Biological Interventions

Biological interventions use organisms (other than humans) to manage pest problems. These organisms are predators, parasitoids, or pathogens of the pest species being managed. Organisms may be directly introduced into the agroecosystem, or conditions within the agroecosystem can be altered to indirectly encourage beneficial organism populations.

Biological interventions are usually highly selective, there are rarely negative side-effects (except in the case of classical biological control) and released organisms are self-perpetuating. Pest resistance is rare, because predators and parasitoids tend to co-evolve with pests, although there are cases of pests developing resistance to frequently applied pathogens. Rearing and release of biological agents is often simple and inexpensive.

Disadvantages include slow action, unpredictability, and incompatibility with pesticides. Using biological intervention effectively requires good observations and a sound understanding of the biology of pest and beneficial.

There are three types of biological control agents.

1. Predators catch and consume pest prey. Major groups of predators include the insect orders Hemiptera, Neuroptera, Diptera, Coleoptera, and Hymenoptera, the Arachnida, and vertebrates such as snakes, birds, and fish. Predators are often fairly generalist, preying on a wide range of prey according to abundance and ease of capture.
2. Parasitoids lay eggs on or in a pest host, which the resulting larvae consume and ultimately kill. Most parasitoids are far smaller than their prey, and therefore mass rearing and release of parasitoids can be relatively convenient. Parasitoids are found only in the insect order Hymenoptera and the Tachinid family of flies (Diptera). Parasitoids usually exhibit high host specificity.
3. Pathogens infect pests with fatal or debilitating diseases and include fungi, nematodes, bacteria, viruses, and other microbes. Fungi, particularly Deuteromycetes, can infect pests externally under favourable conditions, but other pathogens must be ingested to be effective as control agents. Pathogens are very specific to their hosts. Pathogens are often referred to as biopesticides because they can be applied in similar ways to chemical interventions.

Categories of biological interventions are listed below. You may click on each method to view supplementary information about that method.

• Natural biocontrol. Any method that indirectly conserves or increases the effectiveness of existing beneficials in the agroecosystem. This definition can be expanded to include any method which encourages biodiversity, but usually this category encompasses measures that encourage specific beneficials.

Natural Biocontrol: Natural biocontrol takes advantage of the beneficials already present in the agroecosystem by conserving and promoting self-sustaining populations. Birds, bats, snakes, insects, nematodes, fungi, bacteria, viruses and other groups of organisms can contribute to pest management. Well-managed natural biocontrol can handle the majority of pest problems without requiring additional interventions.

In order to promote and conserve beneficials, IPM workers need to know something about their biology. Birds and bats can be promoted by erecting bird and bat houses, respectively, but how does one go about promoting beneficial fungi? Increasing the biodiversity of the agroecosystem will increase natural biocontrol, as will devoting a larger percentage of the total area to non-crop or perennial plantings. Flowering herbs and aromatic plants tend to attract beneficial insects, while compost and organic matter will improve the soil habitat for natural biocontrol.

• Augmentation. The release of beneficials into an agroecosystem in order to help the existing beneficial population control a pest problem.

Augmentation: Increasing the size of natural beneficial populations through augmentation can be an effective way to control specific pests, especially when the beneficial is slow-growing, has had natural numbers reduced, or normally lags behind pest populations. Augmentation is often used to 'tip the balance' in favour of the beneficial population, thereby preventing a destructive peak in the pest population.

Augmentation is a short-term solution, and biocontrol agents that are released in an augmentation release will disperse quickly if the agroecosystem can not provide them with food and shelter. Conservation and creation of habitat for the released beneficial species should accompany augmentation in order to make the releases more sustainable.

• Inundative release. Releasing large numbers of beneficials into an agroecosystem in order to manage a pest problem.

Inundative Release: Inundation is the biological equivalent of a hard chemical pesticide. Large numbers of biocontrol agents are released with the intention of reducing or eliminating the pest population in a short period of time. Normally, the released agent disperses or dies soon afterwards due to lack of food or hosts.

Inundation is effective against pests that only experience a single generation per season or that occur in rare outbreaks. For example, Trichogramma (a parasitoid) is mass-released against cotton bollworm in parts of the United States where only a single generation of bollworm threatens the cotton crop.

Inundation is most often used with pathogens. Pathogens are generally small or micro-organisms, and therefore raising millions or billions of them to release at the same time is logistically feasible.

• Seasonal inoculative release. Releasing a small number of beneficials into an agroecosystem early in the season in order to give the beneficials a 'head-start' on pest populations.

Seasonal Inoculative Release: Seasonal inoculations are used to establish beneficial populations in areas where they previously existed in small numbers or did not exist at all. Usually, the environment into which they are being released has unfilled carrying capacity for the released beneficial. The release of beneficial insects into a recently-planted greenhouse is a good example of a seasonal inoculation.

Seasonal inoculations are a good way to establish a stable pest-beneficial relationship early in the season. By releasing a significant number of beneficials early in the season, pest and beneficial numbers will not fluctuate as widely, preventing pest population peaks that would require additional intervention

• Classical biological control. Introduction of a non-native organism into an agroecosystem or region in order to manage a native or introduced pest.

Classical Biological Control: This original concept of biological control was a response to the release of exotic organisms into agricultural environments. The crops that we are familiar with today in many countries are not indigenous to those countries. Rather, they have been introduced, either historically or recently, often along with their pests.

Where a pest organism is introduced into an exotic environment, the indigenous natural enemies that had controlled its population do not exist. There are many documented instances of pests that seemed innocuous in their native lands becoming huge pests in their new countries. An important example in the Asia-Pacific region is the introduction and spread of the apple snail, which has had a devastating affect on rice cultivation in several countries. In Brazil and Paraguay, where it is native, natural enemies maintain the population of apple snails at less than 1 or 2 per square meter of rice paddy. In Asian rice paddies, however, densities of 300 or 400 per square meter have been recorded.

The obvious reaction to a problem like this is to research what natural enemies exist in a pest's native region and introduce them to the new area where the pest is a problem. While this is a good idea in theory, often the factors which allow particular natural enemies of a pest to control it back home are overlooked or misunderstood. Thus classical biocontrol has seen mixed success, with some introduced enemies doing their job, some being ineffectual, and still others causing even more problems. According to a 1988 study, of 563 attempts to establish classical biocontrol against insect pests, 40% were successful. 31% of releases against weed pests (126 releases) were deemed successful by the same study (Waage, J.K and Greathead, D.J. 1988. Biological control. Phil. Trans. R. Soc. Lond. (B), 318:111-26).

Classical biocontrol is practiced mainly by governments these days, and usually as a last, carefully researched resort. Therefore, it is interesting to most IPM workers, but not particularly practical.

• Herbivores. Managing livestock, insects, and other organisms so that they consume and control weed populations.

Herbivores: IPM often focuses on the management of insect pests, neglecting other taxonomic groups such as vertebrates and plants. Undoubtedly, weeds are a major pest management problem on most farms, and techniques that specifically address weed IPM are an important part of an IPM workers repertoire.

The major natural enemies of plants are herbivores. Unlike the major natural enemies of insect pests, many herbivores have been domesticated by humans, and are much easier to 'release' than predators, parasitoids and pathogens. Cattle, ducks, geese, goats, pigs, chickens, quails, and other vertebrate herbivores are well-known as farm animals but rarely considered for weed control. Properly managed and understood, domesticated herbivores can effectively manage weeds in crops, orchards, forests, and gardens.

Ducks are often used as combined weeders and mollusk removers in rice-based farming systems. Chickens confined to a small area will not only remove weeds, but will also dig up and eat weed seeds. Cattle have selective preferences for certain forages, and can be used to manage crops in otherwise fallow periods. Sheep are used in forestry to prevent undergrowth from choking out young tree seedlings.

3.2.3 Cultural Interventions

Cultural interventions use the way a crop is grown to manage pests. These are often labour-intensive but tend to be kind to the environment. While many cultural controls are considered 'traditional' or modified versions of traditional practices, new methods have been introduced and shown to be effective in cropping systems around the world. Many cultural controls are largely preventative although all methods, whether preventative methods or interventions, are listed here.

Cultural controls can affect pest populations in three ways. First, they can make the crop plant or agroecosystem unacceptable to the pest, and the pest will avoid the crop. Second, they can displace the crop plant in time or space, causing it to be unavailable to the pest during the period when it normally feeds. Third, they can make the agroecosystem a dangerous place for the pest by increasing beneficial populations.

Cultural interventions have been part of agriculture since humans adopted it 10,000 years ago. Partly because of this long development time, and partly because of the diversity of crop husbandry practices used around the world, the following list is very long yet incomplete.

Some cultural interventions are listed below.

• Crop rotation. A crop rotation can be used to interfere with the pests of one crop by culturing another.

Crop Rotation: Crop rotations have long been used by farmers both as a fertility and pest management tool. Planting a succession of different crops in a field over several years prevents the buildup of pests that can occur when the same crop is grown repeatedly. Crop rotations are particularly effective at controlling soil-borne diseases, as well as soil-dwelling organisms that do not disperse well.

Crop rotations work best when the crops in the rotation have few shared pests. A common rotation in temperate areas is maize, wheat, and red clover. Of the 50 or more serious pests that attack these crops, only 3 are important pests of all three crops. Crops with few pests, such as garlic, are often grown in a rotation to break pest cycles.

Some crops directly reduce pest problems for the succeeding crop. African marigolds release an anti-nematodal compound called thiopene, which can reduce nematode loads for subsequent horticultural crops. Cucurbits or sweet potato are often included in a rotation because they tend to choke out persistent weeds.

• Multiple cropping. A quick clean-up crop, or a complementary crop grown in the same season can reduce pest problems.

Multiple Cropping: Multiple cropping, or multicropping, is a cropping system in which several crops are grown in succession within a season. Often the same multicropping scheme is followed year after year. Multicropping is more common where there is distinct seasonality, such as in temperate or monsoonal areas.

The crops grown in a multicropping scheme are often limited by climate or pests. In many tropical countries, wet-rice is grown during the rainy season, followed by cool-season vegetables such as cabbage. If sufficient irrigation or soil water is available, a third, drought-tolerant crop may be grown (e.g. legumes).

Many farmers grow a cereal crop immediately before higher-value crops such as tobacco, cotton, or vegetables. Multicropping a monocotyledonous crop with a dicotyledonous crop effectively disrupts soil borne pests. It also improves weed management, as the persistent monocot weeds of cereals can be easily identified in a dicot crop and vice versa.

• Overseeding/undersowing. Helpful companion crops can be sown into the main crop to control certain pests.

Overseeding and Undersowing: Overseeding and undersowing are farming techniques where one crop is sown into another. Other terms for this operation include relay intercropping, and interplanting. There are many good reasons to overseed. Overseeded crops can increase yields in a season, reduce erosion and improve weed control, depending on the crops involved. However, overseeding can also increase pest management requirements if crops are chosen for criteria other than their IPM compatibility.

Overseeding with IPM principles in mind can be very successful. Brassicas are often undersown with clover to reduce cabbage root fly infestations. In Georgia, USA, farmers who planted cotton into strip-killed crimson clover reduced reduced their use of insecticides and nitrogen fertilizer.

Orchards and plantations are often undersown with annuals, herbs, and other plants with the aim of reducing pest problems. Flowering herbs are commonly used as cover crops in grapes and apple orchards. Traditional shade-grown coffee is interplanted with native shade trees, increasing biodiversity and reducing pest problems.

• Border crops. Crops sown at the periphery of the main crop that specifically prevent pests from entering a crop field or harbour beneficials.

Border Crops: Border crops can be an effective way of controlling pests. Border crops are planted around a field of crops and can consist of a single crop species, a mixture of species, or a mixture of wild species. Border crops can prevent immigration of pests into a crop field and can also harbour beneficials.

Some cereal farmers in the United Kingdom have stopped spraying the outside edges of their fields. They do this to allow partridges to nest undisturbed in the field edges - the partridge is a valuable game bird. A side benefit of not spraying the field edge is that it is home to a high population density of beneficials. While no formal calculations have been made, it is possible that the pest control provided by this unsprayed perimeter compensates for the slightly reduced yields there. (Sotherton, N.W., Boatman, N.D. and Rands, M.R.W. (1989) The 'conservation headland' experiment in cereal ecosystems. Entomologist, 108, 135-43.)
An experiment in California found that some border crops are better than others. Lambsquarters borders were found to be effective at reducing pest problems in cauliflower while mustard and radish increased problems. The choice of a border plant seems to be an important consideration.

• Trap crops. A sacrificial crop that is more attractive than the main crop to particular pests. Often once a trap crop is infested, it is treated with a chemical intervention or physically destroyed.

Trap Crops: A trap crop is a crop that is grown specifically to lure pests away from the main crop. Once the trap crop is infested, it is often sprayed or destroyed. This protects the main crop and reduces the need for pest control measures.

Trap crops have to be more attractive than the main crop. Often, a trap crop is the same species as the main crop, but is a different cultivar or grown in a different way. For example, a small sowing of maize preceding the main crop will effectively trap aerial pests. This is because the earlier sown, taller plants are more attractive to the pests.

Trap crops of different species can be employed as well. Eggplants are more attractive to many potato pests than potatoes are, and small, sacrificial sowings can be used to protect potato crops from various insect pests. Sesame is favoured over cotton by the cotton bollworm (Heliothis spp) and has been investigated as a potential trap crop for cotton in Texas (Laster, M.L. and R.E. Furr. 1972. Heliothis populations in cotton-sesame interplantings. Journal of Economic Entomology. Vol. 65, No. 5. p. 1524-1525.)

• Disease-free plants and seeds. Seed-borne diseases and diseases that are transferred with vegetative planting materials can be eliminated or reduced by using disease-free sources.

Disease-Free Plants and Seeds: Many pest problems are borne on planting stock or seeds. Virus and disease loads on vegetatively propagated stock can reduce yields by as much as 50%. Farmers can greatly improve plant health by starting with clean planting materials. Many countries have certification programs for seed and planting stock. Certified seed is often more expensive than locally available seed but the extra cost should be balanced against the potential risks of using uncertified seed. Vegetatively propagated crops are often grown in tissue culture to obtain disease-free strains.

Some planting materials can be sterilized by the farmer himself. INIBAP has outlined a method for preventing banana disease by using a hot water bath on planting stock. Insect pests can be removed from seed stock by dry heating in an oven. Sunlight, carbon dioxide, steam, and bleach solutions are other low-tech ways to reduce transmission of pest problems through planting stock.

• Altered planting/harvest dates. Planting and harvesting out of synchrony with pest populations can reduce pest damage.

Altered Planting and Harvest Dates: If a particular pest responds to a particular environmental cue, then this pest can be avoided by adjusting sowing or harvesting dates. Sowing may be delayed until after the pest has emerged and dispersed, or the crop can be sown earlier so that it will reach a resistant growth stage by the time the pest emerges.

For example, the hessian fly is a major pest of wheat. By delaying sowing of wheat, the peak of activity of the hessian fly can be avoided and the crop protected. Early planting of sugar cane allows it to reach a size where it is not susceptible to the emergence of borers. Altering the sowing date alters the phenology of the plant, and may expose the crop to other pests at later growth stages. For example, delayed sowing of dry-season crops may expose them to fungal damage if they mature after the start of the rainy season.

• Mulches. Mulches can effectively control pests, in particular weeds and some ground-dwelling insects.

Mulches: Mulches are widely used in agriculture, especially in horticultural crops. The main usefulness of mulches for pest management is that they can effectively control weeds. Mulches also help retain soil moisture, preventing aphid and thrip problems but potentially promoting fungal pests. Mulch can also prevent soil-borne diseases from splashing onto plants during irrigation or rainfall.

Mulch provides habitat for a diversity of beneficials. For example, spiders are abundant in straw or hay mulch, and the use of such mulch in vegetables can result in significant insect pest reduction. Living mulches, such as clover or flowering herbs, are discussed on the overseeding page. These also increase biodiversity.

Plastic mulches are widely used in horticulture, mainly for weed control and to heat cold soils. They can also be used to control some soil borne diseases.

• Irrigation. The amount of water available in an agroecosystem can have a large effect on pest populations. Withholding water or flooding a field are two ways in which irrigation can be used to manage pests.

Irrigation: Carefully managed irrigation can be an excellent way to manage pests. First, applying an optimum amount of water to a crop results in quick-growing, healthy, and pest-resistant plants. Overwatering can cause plants to become lush and prone to fungal diseases and insect such as thrips and aphids. Plants stressed from underwatering wil be less able to withstand pest attacks.

Second, water can be used directly on pests. Strong jets of water can physically knock pests off of plants, flooding a field can drown non-aquatic pests, and newly-irrigated soil particles may swell enough to crush soil-dwelling pests.

Third, water can be used indirectly to control pests. Flooded rice-paddies attract fish, frogs, and other aquatic predators to prey on pests. Raising and lowering water levels in a flooded field can augment predation of above-water pests by aquatic predators. Adjusting irrigation can speed or slow crop maturity, preventing a crop from ripening at the same time as a pest population peak.

• Fertilization/manuring. Soil fertility affects the growth and composition of a crop, which in turn affects its susceptibility to various pests.

Fertilization: Fertilization and manuring indirectly reduce pest problems by contributing to healthy plants. Fertility management can also be used directly to control weeds and plant diseases.

Soils with adequate, balanced fertility result in quick-growing, healthy plants that resist pests. Fast-growing plants reduce opportunities for pests that attack certain growth stages, such as stem-borers, by shortening their period of vulnerability. Fast-growing plants can also compensate for damage that does occur. Fast-growing plants quickly form a canopy, discouraging pests that disperse aerially or seek bare ground.

Although high fertility can increase potential yields, balanced fertility that is appropriate to the intended crop is the key to pest prevention. Many diseases and insect pests are associated with too much nitrogen fertilizer in proportion to phosphorous, potassium, and other elements. Similarly, several pest problems have been managed using a disproportion of specific trace elements, such as silicon or zinc.

Building balanced soils through the addition of compost and organic matter can help reduce nutrient imbalances. Relying on non-chemical sources for at least part of a crop's fertility requirements can indirectly reduce pest problems.

• Pasturage. Grazing animals in a crop field before, during or after harvest can reduce pest problems.

Pasturage: Grazing animals can be thought of as another 'crop' in crop rotation or multicropping scheme. Domestic cattle, buffalo, pigs, ducks, poultry, and fish can drastically change the nature of a crop field through their grazing activities.

Grazers can reduce pest populations in a crop field. Poultry dig and scratch soil with their feet, overturning and consuming insects and weed seeds. Ducks consume small weeds and mollusks, and are particularly useful for controlling rice-field pests. Larger animals crop weeds, till the soil with their hooves, and leave behind manure.

• Efficient harvest and storage. An efficient harvest can break pest cycles and result in clean product. Properly managing storage pests maintains value of the stored crop and prevents it from becoming a pest vector for future crops.

Efficient Harvest and Storage: A clean, well-timed harvest can prevent pest problems in the harvested and future crops. Proper sanitation measures should be followed, and crop materials that can harbour pests until the next season should be removed. Crops should be harvested at the proper growth stage. Harvesting early or late can cause pest problems in storage.

Crops should be properly handled before storage. Drying, curing, and other primary processing activities should be planned and carried out with IPM in mind. If a crop is going to be machine dried, for example, part of the drying cycle could be at a high enough temperature to kill any potential storage pests.

Managing pests in stored crops is a challenge for most IPM practitioners. Pests can rapidly multiply and damage large portions of a stored crop but they are often hard to detect. Stored crop is often neglected until it is time to eat or sell it - this is too late to apply appropriate interventions!

Stored crop IPM follows the same procedures as field IPM. First, store the crop in a way that prevents pest problems in the first place. Second, monitor for pests, identify any found, determine whether they will cause economic damage, and intervene if necessary.

3.2.4 Physical Interventions

Physical interventions alter or exploit a physical characteristic of the environment in order to manipulate pest populations. Different temperatures, humidity levels, and even atmospheres can be used to manage pests, as can mechanical intervention such as tillage and shredding. In situations where the farmer has a large degree of control over the physical environment, such as greenhouses, physical interventions can be the most important methods of IPM. Even in field situations, physical manipulations such as compaction, flooding, or mulching can adversely affect potential pests.

There are probably hundreds of physical interventions used by the world's farmers. Six categories of physical interventions are listed here. You may click on each category to view supplementary information.

• Direct. Physical interventions that involve the direct physical removal or destruction of the pest. Examples include weeding, destruction of crop residues, pruning, and vacuuming.

Direct Physical Interventions

Traps: Traps are often used for monitoring pest populations, but trapping can also be used for control. Many kinds of traps exists. Banding with sticky bands or bands impregnated with repellent can exclude pests from tree crops. Light, colour, pheromones, fermentation, and sound can all be used to lure pests into traps. Trap crops are discussed on a different page, but plant parts from the main crop can also be used for trapping and destroying pests.

Shaking: Shaking crop plants can dislodge pests to groundsheets where they can be collected and destroyed.

Handpicking and weeding: Hand picking and destruction of pests is widely practiced wherever labour and time are available.

Pruning: Pruning to remove egg masses of pest insects can be an effective way of controlling orchard and ornamental pests.

• Tillage. Physical manipulations of the soil that help to manage pests. Compaction, soil shaping, and no-till cropping are included in this category.
• Barriers. Physical barriers, such as greenhouses, screens, or mulches, which prevent a pest from reaching a crop.

Barriers: Barriers act to physically prevent pests from feeding or laying eggs on a crop. Several types of barriers are described here.

Screens: Screens are commonly used in greenhouses to allow circulation of air but prevent entry of pests. Screenhouses are similar to greenhouses, except that their outer covering consists of screening that is appropriately sized for the target insect. Screens can also be used in fields to protect valuable plants.

Greenhouses and other structures: Built structures that can be closed off from the outside environment can very effectively exclude pest organisms. Greenhouses provide protection not only from extreme weather and temperatures, but also from dispersing pests. Many greenhouses can be sealed for fumigation, which is often required if pests establish a population inside.

Row covers and mulches: Row covers and mulches are placed on the ground around the stems of the crop plants. They are effective against soil-born pests such as cabbage maggots.

Trenching: Some insect pests are unable to escape from trenches, and lining a crop field with a trench can provide substantial protection. For example, Colorado potato beetles are trapped by a 'V'-shaped tranch with a sharp slope, resulting in substantial reductions in adults and egg deposition within potato crops.

Bags: Valuable fruits are sometimes covered with individual bags. This method is time-consuming and labour-intensive, but can lead to premium prices for the resulting unblemished fruits. Entire bunches of bananas can also be protected bby using large bags.

Packaging: Many materials have been developed that physically exclude pests from stored crop products. These include metal foils, plastics such as cellophane and polyproylene, and paper.

Fences: A well-built fence can protect crops from many pests as long as it is properly installed and maintained. In particular, mammals and low-flying insects can be excluded by good fencing. Floating row covers.

Nets: Nets placed over fruit trees or other

• Temperature. The use of heat to manage pests. Examples include soil solarization, flaming, burning, etc.
• Water. Manipulation of moisture levels to manage pests. Flooding is an example.
• Air. Manipulation of the atmosphere to manage a pest. This method is usually associated with storage of harvested product in high-nitrogen or high-carbon dioxide environments.

3.2.5 Genetic Interventions

Genetic interventions manipulate or exploit the underlying genes, chromosomes, and reproductive systems of crop, pest, and beneficial populations. The major genetic intervention used in agriculture today, breeding for host-plant resistance, has had a profound effect on IPM for most major crops. Induced sterility, although potentially widely applicable, has seen limited use since its initial success with screw-worm fly (Cochliomyia hominovorax) in the early 1950's.

Genetic interventions are attractive to IPM workers because they are perceived as being highly specific, precisely controllable, and limited only by the imagination and creativity of scientists. Genetic interventions can be packaged, propagated and delivered in a form that is readily acceptable and easy to use - seeds or other planting materials. They are self-perpetuating, do not pollute the environment through spray drift or run-off, and are affordable. The success of the Green Revolution was dependent on host-plant resistance bred into key crops, and many advocates of genetic engineering envision a second Green Revolution based on the latest molecular advances.

For these reasons, the development and application of genetic engineering and gene mapping is expected to have a major impact on IPM. Already, many crops have been bred for increased host-plant resistance using genetic material from other species. Other crops have been altered to allow other interventions, such as herbicide application, to be performed more easily. Whether some, none, or all of these genetically-engineered crops should be included in an effective IPM program is the subject of heated debate and there is not yet any kind of agreement about the safety, benefits and risks of genetic engineering in IPM. Critics of genetic interventions in IPM point out that dependence on 'silver bullets' for pest management is a reversion to the calendar spraying mentality that caused many of the pest management problems that exist today. A crop that has a systemic pesticide engineered into its genome is a clever invention, but growing it in a way that induces pest resistance (such as large-scale monocultures) is not IPM. Workers who want to include genetic interventions in an IPM program need to remember that the I stands for Integrated. They should try and complement genetic interventions such as herbicide resistance and engineered systemic pesticides with more traditional techniques such as crop rotations and biological control.

While it is beyond the scope of this course to deal with this topic in much detail, interested participants may want to read the following series of position papers to better understand the complex issues and diversity of viewpoints.

1. Ten reasons why biotechnology will not ensure food security, protect the environment and reduce poverty in the developing world. Altieri, M.A. and Rosset, P. (1999). AgBioForum, 2(3&4), 155-162.
2. Ten reasons why biotechnology will be important to the developing world. McGloughlin, M (1999). AgBioForum, 2(3&4), 163-174.
3. Strengthening the case for why biotechnology will not help the developing world: a response to McGloughlin. Altieri, M.A. and Rosset, P. (1999). AgBioForum, 2(3&4), 226-236.

Some genetic interventions are listed below.

• Host-plant resistance. A wide range of breeding programs have developed crops with resistance to one or more major pests.

Host-Plant Resistance: Crop varieties that are bred to resist certain pests are an important component of IPM. Such varieties tend to reduce pesticide use, require little change in farming practices, and are seen as the easiest way to pass high-level research results directly to farmers. Host-plant resistance is most effective when integrated with other techniques, however. Massive plantings of resistant varieties can cause pests to become 'resistant to the resistance', forcing plant breeders to breed new varieties to replace old, ineffective ones.

Crop plants can resist pests in three main ways.

• Nonpreference. The crop plants are avoided by the pest because they do not 'like' it.
• Antibiosis. Plants cause a reduction in the biological performance of the pest.
• Tolerance. Plants can tolerate the pest and still provide an adequate yield.

The mechanisms of resistance are diverse. Crops resist pests through color, palatability, hairiness, waxy coatings, gross morphology, gumminess, necrosis, hardness, phenological shifts, toxin production, nutrition, integration with biological control, and compensation. Each mechanism of resistance may be classified under one of the three main types above.

Many resistant varieties have lost their resistance through mass plantings and adaptation of pest populations. Resistance management plans are designed to reduce or prevent the development of resistance, by planting resistant varieties in a particular way. For example, many maize growers will grow a strip of an older, susceptible variety around a new resistant variety so that the pest has something preferrable to eat and will maintain its current resistance status.

• Sterilization. Releasing large numbers of sterile male insects into an agroecosystem can quickly reduce the local pest population.
• Genetic displacement. Replacement of a wild pest population with a population that has been bred to be less of a pest problem.
• Genetic improvement of beneficials. Breeding and release of improved beneficials into the agroecosystem.

3.3: Regulation

Regulatory and legislative approaches to IPM operate at an organizational level that is larger than a field or farm. They manage pests on a regional or national level. Many types of pests, such as migratory pests or those that have been accidentally introduced, can be controlled effectively through regulatory interventions. Many cropping regions enjoy comparative advantages over other regions due to successful quarantine and eradication programs against major crop pests.

Regional or national programs to manage pests rely on cooperation by (and enforcement of) individual farmers, and in many countries effective regulatory interventions are difficult or impossible to achieve. As international trade of crops and crop products increases, so does the potential that new pests will be introduced into previously pest-free areas. Sometimes, regulatory interventions have little to do with practical pest management, but are used to protect domestic producers from competition with cheaper imports.

Some regulatory interventions are listed below. You may click on each method to view supplementary information about that method.

• Quarantine. Preventing the introduction of known or unknown crop pests by excluding infected materials and vectors from a particular region.
• Eradication. Regional campaigns that aim to completely eliminate a particular pest.
• Control districts. Areas where particular plants or other organisms are prohibited due to their status as alternate hosts for major crops.
• Crop-free periods. Attempts to eliminate pests that move from old crops to younger crops by cutting off their food supply for a designated period.
• Planting time restrictions. By enforcing a planting time for a particular crop, pests that emerge on predictable environmental cues can be managed.
• Enforced growing of particular cultivars. In areas where pest problems are endemic, enforced growing of resistant cultivars can reduce populations permanently.
• Compulsory sanitation measures. Strict sanitation measures, such as burning of residues or burying diseased animals can prevent the spread of persistent pests.
• Regional diversification. By promoting and coordinating crop diversification on a regional scale, area managers can reduce the pest problems that are associated with a dominant monocrop.
• Isolation. Growing valuable crops in an area that is physically isolated from important pests can, along with quarantine, result in sustainable, efficient production.

Legislation can be a very effective tool in the promotion of IPM on a large scale. Perhaps one of the most famous IPM programs in the world, the Indonesian Rice IPM program, was based on legislation.

Large-scale implementation

Implementing IPM at a national or international level is the role of governments, larger NGOs, and IARCs. The lobbying, promotion, and reform required to change legislation, institutions, and popular perceptions related to IPM is well beyond the scope of this course! Adoption of IPM on a large-scale is infrequently achieved, although there have been some success stories, such as the implementation of rice IPM in Indonesia during the 1980's, described below.

Indonesian Rice IPM

Indonesia was at one point the world's largest importer of rice, but Green Revolution varieties led to self-sufficiency by 1984. Due to regular spraying and widespread planting of pest-resistant varieties, pest problems began to increase in severity. For example, 350 000 tons (worth US$100 million) was lost to brown planthoppers (Nilapavarta lugens) in the 1976-77 season despite heavy spraying. By 1986 the Indonesian government was subsidizing rice pesticides by US$100 million per year.

In 1986, a Presidential decree banned 57 broad-spectrum pesticides for use on rice, and subsidies for the remaining narrow-spectrum pesticides on the market were gradually reduced until 1989, when they were withdrawn. In infected areas, only brown planthopper resistant varieties were allowed to be grown, and IPM was massively implemented through intensive farmer training, reorganization of research institutes, and widespread publicity. Indonesian IPM in rice is considered by many to be the most successful implementation program ever conducted.

aglearn.net - Copyright 2004 - CropLife Asia
25F, Rasa Tower, 555 Phaholyothin Rd., Chatuchak, Bangkok, 10900. Thailand.
Telephone: +66 2 937 0487; Fax: +66 2 937 0491
Home - Responsible Pesticide Use - Introduction to IPM - Cotton IPM - Rice IPM - Vegetable IPM - Soil Fertility Management - Contact Us