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EAP Publication - 58

Pest Control-Cultural Control of Insects

CULTURAL METHODS OF PEST, PRIMARILY INSECT, CONTROL

Dr. Stuart B. Hill
Macdonald College of McGill University
Ste-Anne de Bellevue, QC, Canada H9X 3V9

INTRODUCTION

Cultural controls are the oldest methods that have been used to manage pest populations. However, with the development of synthetic pesticides these controls were rapidly abandoned or de-emphasized and research on them was largely discontinued. Because cultural controls are preventative rather than curative they are dependent on long-range planning. Also, because they are dependent on detailed knowledge of the bio-ecology of the crop-pests-natural controls-environment relationships, most of which, in the past, were poorly understood, the results were very variable, and it was often difficult to evaluate their effectiveness. It is understandable that most farmers were eventually won over to the, at first, more reliable and less knowledge- and skill- dependent toxic chemical solutions to pest problems.

Today the situation is very differnt from those early days of pest control. We have a much better understanding of the bio-ecological relationships within crop systems; predictive computer models are available for some pests; and the social climate is demanding reduced dependence on toxic chemicals to solve problems. Such concerns have developed as a result of numerous pesticide accidents, detection of residues in recreational environments, drinking water, foods and human tissues, the increase in the incidence of pesticide-related allergy and petrochemical sensitivity, the growing interest in the relationships between food quality and human health (and the associated expanding organic food market), the decreasing effectiveness of many pesticides as more and more pests become resistant to them, and their increasing costs.

Pest control scientists have responded to this situation by promoting a philosophy of pest management and integrated pest control (IPM). At first these approaches, encouraged by the chemical companies, emphasized the efficient use of pesticides, claiming that problems associated with these poisons could usually be traced to their misuse. However, there is ample evidence that problems often arise even when pesticides are used as recommended. This is not surprising as pesticides are largely non-selective and are as lethal to the 99.9% of insect species that are beneficial or neutral with respect to humans, as to the 0.1% that are pests; and most correctly applied pesticide still misses its target. Because of these and other problems associated with pesticides it seems reasonable to expect that we will eventually have to restrict their use to socially important emergencies (for example, in the future, control of a tobacco pest may not be regarded as a socially important emergency.)

The next strategy in the development of IPM was to search for more benign substitutes for pesticides: hormones, sex attractants, traps, biological control agents, including bio-engineered pathogens, release of sterile males, etc. Such approaches, although useful as less intrusive curative methods, still avoid confronting the causes of the problem. They keep the farmer dependent on experts and suppliers of products, and they perpetuate the image of pests as enemies to be eliminated.

We are now on the threshold of a third phase in the development of IPM systems that recognizes pests not as enemies, but as indicators of problems in the design and management of systems. It is also becoming clear that ecological knowledge holds most of the keys to appropriate environmental designs and methods of management capable of keeping pest numbers below unacceptable levels. In this approach, potential pests are prevented from becoming problems by means of the integration of a range of cultural and bio-ecological controls. The more familiar intrusive controls, including certain pesticides, are then reserved for emergencies.

Further advances in this approach are are dependent on identifying and responding to the barriers to the development and implementation of cultural methods of pest control (and their integration with other agricultural goals and practices). Foremost among these are the lack of appropriate research, training, services, equipment, and crop species and cultivars. In addition to responding to these deficiencies, changes in human values and attitudes will also be required: a shift in emphasis from cosmetic to nutritional quality; and from pest elimination to management below thresholds related to our values.

In their present forms, cultural controls do not offer a panacea for pest prevention and control. These approaches range from the environmentally supportive, knowledge- and skill-intensive techniques, such as the optimal design and management of agroecosystems in time and space (e.g., the design of integrated polycultures, management of adjacent environments, use of companion crops, rotations, timing of seeding, harvesting and field operations, etc.), to the more heavy-handed interventions that can result in soil erosion and environmental degration (e.g., excessive cultivation, summer fallowing, burning of crop residues, flooding, destruction of uncultivated areas containing alternative hosts of pests, etc.). In the following survey I have endeavored to emphasize the former group of approaches.

Cultural controls employ practices that make the environment less attractive to pests and less favorable for their survival, dispersal, growth and reproduction, and that promote the pest's natural controls. The objective is to acheive reduction in pest numbers, either below economic injury levels, or sufficiently to allow natural or biological controls to take effect.

STRATEGIES ON WHICH CULTURAL PRACTICES ARE BASED:

i) Make the crop or habitat unacceptable to pests by interfering with their oviposition preferences, host plant discrimination or location by both adults and immatures.

ii) Make the crop unavailable to the pest in space and time by utilizing knowledge of the pest's life history, especially its dispersal and overwintering habits.

iii) Reduce pest survival on the crop by enhancing its natural enemies, or by altering the crop's susceptibility to the pest.

To design and implement cultural controls, it is necessary to have accurate knowledge of crop and pest biology, ecology and phenology, and of the weak links in pest-crop interactions.

ADVANTAGES:

Cultural controls are generally the cheapest of all control measures because they usually only require modifications to normal production practices. Sometimes they do not even require extra labour, only careful planning. Often they are the only control measures that are profitable for high acreage of low value crops.

Cultural controls are dependable, and are usually specific. Of major importance is the fact that they do not possess some of the detrimental side effects of pesticides, namely the creation of resistance to pesticides, undesirable residues in food, feed crops and the environment, and the killing of non-target organisms.

DISADVANTAGES:

Cultural controls require long-term planning for greatest effectiveness and they need careful timing. They are often based on the substitution of knowledge and skills for purchased inputs and, as such, are more demanding on the farmer's competence. They may be effective for one pest but may be ineffective against a closely related species.

Effectiveness of cultural controls is difficult to assess and they do not always provide complete economic control of pests.

Some cultural controls have adverse effects on fish and wildlife and may also cause erosion problems.

CULTURAL CONTROLS INCLUDE:

SELECTION OF SITE:

PLANTING DESIGN AND MANAGEMENT:

MAINTENANCE OF SITE:

clean field borders

weed control

HARVESTING PROCEDURES:

DESCRIPTION OF THE METHODS

SELECTION OF SITE:

-Sometimes a pest can be avoided by selecting a planting site that is ideal for the crop and the natural enemies of the pest, but unfavorable for the pest itself. Factors to consider include the history of the site (e.g., whether the pest has occured in this location in the past), its proximity to potential overwintering sites (woodlots, hedges, field borders, etc.) or sites with abundant natural controls (hedges, field borders and bodies of water), climate, microclimate, topography, elevation, slope, aspect, soil conditions, weed species, etc. One key is to avoid stressing the crop. When plants are grown in stressed conditions, they tend to emit signals that attract certain pests.

PLANTING DESIGN AND MANAGEMENT:

- crop isolation: the location of crops with respect to one another and their degree of isolation can affect their likelihood of being invaded by pests. Isolation from old crops of the same type, and from closely related indigenous host-plants that act as sources of pests, is one way of reducing the probability of attack. The chance of invasion occurring will, however, increase with time. Hence, this practice is most appropriate for annual crops, especially when climatic conditions are not ideal. Separation of sequentially planted crops in time to disrupt host-plant continuity and prevent easy pest dispersal may be useful, e.g., for carrot fly control.

Note: crop isolation can be made more difficult by the proximity, in the surrounding fields or in nearby uncultivated areas, of wild plants that act as reservoirs both for pests and for pathogens transmitted by them. This method of cultural control requires cooperation of from neighboring producers.

- planting density and spacing: the primary objective of this cultural method is to maximize yield per unit area without reducing crop quality, so that yield advantages overide pest incidence reduction. It can also be used to reduce pest numbers and damage. Spacing may affect the relative rate of growth of the plant and its pest population per unit of time, and the behavior of the insect pest in searching for food or for an oviposition site. It is based on the following observations:

i) close spacing may add to the effectiveness of natural enemies and result in greater control of a pest population;

ii) some insect pests are attracted by low density planting because they are silhouetted against bare ground, e.g., at low density brassicas attract more aphids;

iii) some populations of pests can increase on high density crops. Because of the variety of existing responses to crop spacing, a detailed knowledge of the pest's biology is of extreme importance.

Plant spacing is also used to promote vigorous and strong plants, which in itself can be a good cultural control measure, e.g., a good protection for corn against corn stalkborer.

Plant spacing that encourages rapid crop maturation could also provide a means of encouraging early fruiting and harvesting of crops of indeterminate flowering plants. This has been used in the south against bollweevils and pink bollworms.

- mixed cropping: in this approach, more than one crop is grown on the same piece of land. This reduces phytophagous insect pests by encouraging increases in natural enemies due to:

i) greater temporal and spatial distribution of nectar and pollen sources;

ii) increased ground cover, particularly important for diurnal enemies;

iii) increased prey, offering alternative food sources when the pest species are scarce or at an appropriate time in the predator's life cycle. It also affects the pest's ability to find host plants by conferring associational resistance, by the non-host plant masking the odors of the host plant.

- timing of seeding and planting: this is used largely to:

i) avoid invasion by migrants, or the oviposition period of particular pests, and the introduction of disease in the crop by insect vectors;

ii) to synchronize the pest attack with its natural enemies, with weather conditions that are adverse for the pest or with the abundance of an alternative host;

iii) to make it possible to destroy the crop before the pest enters diapause.

Timing can be used to allow young plants to establish to a tolerant stage before attack occurs, to reduce the susceptible period of attack, to mature the crop before a pest becomes abundant, to allow it to compensate for damage and to fill gaps where plants have been damaged or killed, and to avoid the egg-laying period of a particular pest.

- crop rotation: an effective rotation is one in which a crop of one plant family is followed by one from a different family that is not a host crop of the pest to be controlled. Most common rotations include grasses, legumes and root crops. Rotations are effective against pests that have a limited host-plant range and dispersiveness and/or that cannot survive for more than one or two seasons without suitable host crops. Pests most subject to this type of control are poorly mobile, soil-inhabiting species with a restricted host range and a life cycle of 1 year or longer.

- destruction of volunteer plants: such plants are very attractive to many insects and serve as the focal point for future infestations. Unless they are destroyed they can help perpetuate a pest problem by furnishing a food source to long life-cycled pests of preceeding crops.

- management of alternate hosts: many insects reproduce on weeds or other alternate hosts and then attack the main crops. It is therefore usually desirable to destroy brambles or other weeds on uncultivated land to assist in the control of insects such as aphids, beet leafhopper and raspberry caneborer. Care must be taken, however, not to destroy nursery sites for the pest's natural enemies.

- management of trap crops: trap crops (often small plantings, often made earlier than the main plantings) are used to divert insect attack away from the crop at risk by using more attractive food sources. The trap crop must usually be destroyed before the insects reproduce.

This method involves the planting of a crop upon infested land so that the pest is stimulated to attack, but the crop is either removed before the pest can complete its life cycle or it will not provide all the requirements necessary for the completion of the pest's life cycle. Alternatively the trap crop may be preferentially attacked in the presence of the crop one needs to protect.

Note: the pest must have a narrow host range and the trap crop species selected need not be different from the main crop.

- management of nursery crops: like trap crops, these are plants that are more attractive to the pest than the commercial crop, but in this case the aim is to provide a site where both pests and their natural controls can build up, the latter dispersing to the crop and providing effective control.

- management of surrounding environments (field borders, hedges, adjacent woodlots and bodies of water): these habitats can be designed and managed to provide ideal conditions for the natural enemies of pests. Often this involves providing suitable flowering plants for predators and parasites of pests and making such sites unsuitable for overwintering pests, e.g., coniferous litter around an orchard makes the woodlot unattractive to overwintering plum curculio, thereby forcing them to overwinter in the orchard where they suffer higher mortality than in a suitable woodlot.

MAINTENANCE OF SITE:

- cultivation, tillage: this approach can help in the control of soil inhabiting forms of field crop pests by:

i) bringing larvae and pupae onto the soil surface, thereby exposing them to desiccation and predation, freezing and thawing;

ii) damaging the pest in its soil inhabiting phase, e.g., wireworms;

iii) destroying crop residues, which might harbour pests that could invade new crops;

iv) burying residues so deep that emergence from eggs or pupae is made impossible.

Note: minimum tillage and direct drilling may, depending on habitat conditions, increase or decrease pest presence, so knowledge of the bioecology of the particular pests that are present is essential.

- fertilization, liming and manuring:

i) plant nutrition can influence the feeding, longevity and fecundity of phytophagous pests; the common fertilizer elements (nitrogen, phosphorous and potassium) can have direct and indirect effects on pest supression. In general, nitrogen in high concentrations has the reputation of increasing pest incidence, particularly of sucking pests such as mites and aphids. On the other hand, phosphorous and potassium additions are known to reduce the incidence of certain pests, e.g., in low phosphorous soils wireworm populations often tend to increase;

ii) fertilization promotes rapid growth and shortens the susceptible stages. It gives better tolerance to, and opportunity to compensate for, pest damage. Trace mineral and plant hormones sprays (e.g., from seaweed extracts) have been found to reduce damage by certain pests, particularly sucking pests such as some aphids and mites.

- timing of tillage and fertilization operations: this may affect pests favorably or unfavorably. Efforts should be made to avoid damage and stress to plants, and also overfertilization, thereby avoiding making the crop particularly attractive and susceptible to pests.

- pruning, defoliation and topping: during the dormant phase, removal and destruction of dead, diseased, or infested wood can greatly reduce overwintering stages of pest populations and thus their spread the next year, e.g., mite eggs, aphids, scale and fire blight infested terminals. In apples and other fruit trees, pruning water sprouts, sucker growth or foliage that is prefered by aphids, helps control these pests. Pruning that is excessive, (e.g., in relation to fertilization practices), can increase the population of certain pests such as mites, aphids, and leafhoppers.

- irrigation, drainage: moisture is an important limiting factor that affects the survival of some pests. Where sufficient water is available, flooding is sometimes used for insect and nematode control, e.g., flooding of infested soils in the northwestern part of the United States has been used to eliminate certain species of wireworm within three days. Certain other wireworm species are unable to withstand desiccation. Where these wireworms occur, drying out the soil is an effective control measure.

- sanitation and crop residue destruction: this method is used to reduce pest infestation through the removal of breeding and hibernating sites. Sanitation has broad applicability; to be most effective, it requires knowledge of the habits of the pest species and careful timing. It involves:

i) eradication of harmful weed hosts or alternate hosts;

ii) timely destruction of crop residues;

iii) cleaning of field borders of alternate hosts, and removal of scrub or shelter in which pests might hide; e.g., in orchards, destruction of cull or dropped fruits and pupation sites for codling moth, apple maggot , and plum curculio may be achieved by means of livestock, and suction or cultivation equipment.

Note: if total crop residue destruction is required, problems with wind erosion, water runoff and soil moisture loss can occur.

- mulches: natural or synthetic soil coverings may encourage or discourage pests. Plastic mulches may exclude soil pests, and organic mulches may permit their control by providing a suitable habitat for their natural enemies. Crop residue mulches around fruit trees can help control a number of pests of fruit, but the trees will need extra protection from mice, which also tend to become more abundant.

HARVESTING PROCEDURES:

-timing of harvesting: early harvesting can be used to disrupt survival of the pest in its habitat. Also, clipping or early harvesting can be helpful in destroying immature insects that are in the foliage.

- strip harvesting: in this system, crops are harvested in alternate strips, so that two different aged growths occur simultaniously in a field. When one series of strips is cut, the alternate strips are about half grown and the field becomes a rather stable environment. This is used in alfalfa, where Lygus bugs are a problem. They move into the younger hay strips as the older ones are harvested, instead of flying to other crops as they do if the entire field is cut at one time. Since natural enemies of the Lygus bug also move from strip to strip, there is no increase in the Lygus population. When the Lygus adults move into the uncut strip, they deposit eggs in the half-grown hay, but, since the hay is cut in about 15 days, many of the eggs and newly hatched nymphs are removed or destroyed at harvest.

IMPLEMENTATION OF CULTURAL CONTROLS

For the above cultural controls to achieve their potential, the following initiatives will need to be taken.

1. Policy

Governments will need to establish a clear food and agriculture policy that recognizes that the primary function of the food system is to nourish all members of the population in a sustainable way, and without infringing on the earth's capacity to meet the other basic needs of present and future generations. Such a policy would necessarily have to identify appropriate strategies for the management of agriculture pests. As a first step towards this, a committee could be established (with representation from the appropriate departments, together with representation from the appropriate private and public sectors) to draw up such a policy for public discussion and subsequent implementation.

2. Legislation

Legislation should be established to permit the appropriate government departments to, if necessary, develop regulations that would require farmers to cooperate in the application of certain cultural control programs, e.g., collection and destruction of June drop and fallen apples in orchards; destruction of certain types of prunings and crop residues, synchronized planting and seeding of certain crops; destruction of alternative hosts of certain pests, etc. Such regulations already exist in several European countries and in Australia.

Legislation is also needed to ensure that users of Class 1 and 2 pesticides have not only achieved competence in the "safe" use of pesticides, but are also competent in the use of safe alternatives, including the relevant cultural controls.

Governments should also evaluate how their curent programs, policies and regulations encourage farmers to use pesticides, e.g., programs that inadvertently encourage the use of pesticides to meet top grading standards based on cosmetic appearance.

3. Research

Governments must designate appropriate amounts of money to support the establishment of research related to sustainable systems of food production, including the use of cultural methods of pest control.

A list of priorities should be established, with emphasis on long-term participatory (on-farm), multidisciplinary team research. With the trend to fund research through matching grants with industry, it is imperative that areas such as cultural controls, which tend to be based on processes rather than products and therefore of little interest to most industries, be designated as priority areas for support by government.

To stimulate interest in this area among researchers, governments should provide funds to hold conferences on cultural and other alternative methods of pest control and to invite keynote speakers from around the world.

Research in this area should be done both in-house and through the awarding of grants to researchers in universities, the private sector, and also to farm organizations and innovative farmers.

There is already a feeling in many government circles that funds for pesticide research, especially testing and evaluation, should be phased out in favor of research into alternative control strategies; and that monies for pesticide research be provided by the pesticide industry.

4. Services

At the present time a widely reported complaint by farmers wishing to avoid the use of pesticides is that most extension agents or agronomes are unable to help them solve their pest problems. To correct this situation short courses should be provided for these agents to enable them to become familiar with alternative strategies, including cultural methods, for controlling pests. Supports should also be provided to individuals seeking to establish themselves as companies selling services and supplies relating to safe alternative controls, including cultural controls.

5. Training and Education

The success of most of the above recommendations are dependent on widespread access to comprehensive educational programs covering the design and use of cultural controls. Options include support for a university "chair" in this area, for the establishment of courses in cultural controls, and for the preparation of appropriate teaching materials and demonstration plots.

6. Public Education

Although public awareness is shifting, much work still needs to be done to help the public to realize that most insects are beneficial and that cosmetic quality of food is not a reliable indicator of nutritional quality. A greater appreciation of the essential role of the farmer in society is called for, and an expanded responsibility for considering our actions in relation to the needs of future generations. A creative and intensive public education campaign should be mounted to get these messages across.

CONCLUSIONS

In this brief summary, cultural methods of pest controls have been described under the headings of selection of site, planting design and management, maintenance of site, and harvesting procedures. Implementation of these controls are discussed in relation to policy, legislation, research, services, training and education, and public education.

Copyright 1989 Ecological Agriculture Projects


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