The cultural control measures of pests include those regular farm operations, that do not require the use of specialized equipment or extra skills, designed to destroy pests or to prevent them from causing economic damage.

Often these are by far the best methods of control since they combine effectiveness with minimal extra labor and cost.

Most of the cultural methods do not give high levels of pest control, and in the recent past, when reliance was placed almost entirely on chemical control (using organochlorines), these methods received little attention.

However, with the recent interest in integrated pest management, there is a revival of interest in the use of cultural methods for incorporation into management programs.

Often the present-day scheme is to use several different methods in conjunction, each method achieving a certain level of control, so that in concert the desired level is achieved with minimal ecological disruption, etc.

Cultural Control Measures of Pests

1. Optimal Growing Conditions

A healthy plant growing vigorously has considerable natural tolerance to pests and diseases (as with a healthy animal), both physically and physiologically.

Good plant vigor is a result of sound genetic stock and optimal growing conditions. Obviously, the farmer attempts to provide such growing conditions so that the crop yield will be maximal.

Many diseases are more severe, and the damage by pests is more serious if the plant is suffering from water stress (drought), unfavorable temperature, imbalance of nutrients or nutrient deficiency, etc.

This predisposition to pest attack and disease can be very serious when crops are grown on marginal land. This is one main reason, together with reduced yield, why the cultivation of marginal land is generally not very successful.

This point is of particular interest at the present times, for various countries are endeavoring to increase their national agricultural yield, partly to produce more food crops to feed the ever-increasing population, and partly to increase the cash crops as a source of national revenue.

But the great majority of countries are already utilizing all their high-quality agricultural land and the only land available for agricultural development is marginal tracts with a very limited potential.

In some countries this situation is exacerbated in that land has to be taken from agriculture in order to provide sites for new towns, airports, and the general ever-increasing sprawl of urbanization; such land is almost invariably choice agricultural land and maybe the finest such land in the country (that being the main reason for the historical siting of the town in that location).

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2. Photosynthetic Efficiency

When aiming at a maximum level of sustained crop yield it is advantageous to understand the physiology of the crop plant in order that cultivation is practiced in the most effective manner.

This is also important in some countries where cultivation of marginal land is being undertaken, for only certain crops give adequate yields on poor land. Plants struggling in poor growing conditions are invariably more susceptible to damage by pests.

Some plants are now known to have more efficient photosynthetic activity than others. They are referred to as C4 plants – so named because of the chemical intermediary, the four-carbon oxaloacetic acid.

The majority of plants, which could be called the ‘normal’ plants, are referred to as C3 plants; C4 plants generally have high productivity in situations of high temperature and low humidity (and the concomitant low carbon dioxide concentration).

They have a high level of stomatal resistance, which conserves water at high temperatures, but of course, restricts carbon dioxide entry, but they are able to carry out photosynthesis very effectively under low carbon dioxide concentrations. As a group, these plants are generally the most productive agriculturally.

Examples of C4 plants include maize, sugarcane, and other tropical Gramineae as well as many weed species in the Chenopodiaceae, Euphorbiaceae, etc. The more effectively functioning plants are generally those with the highest agricultural yields, and are also often more tolerant of insect attack and less susceptible to damage.

The importance of shade has been somewhat misunderstood in the past; several crops have in the past been thought to require shade for best growth and production; in some cases, because they are naturally occurring forest understory plants and to be regarded ecologically as skiophytes (i.e. shade-tolerant).

A striking example is a tea – for some obscure reason tea was thought to need shade, and many plantations bear mute testimony to this previous practice in the large number of dead trees to be seen standing throughout the plantation.

Recent experiments in Indonesia have shown that cocoa grown as a heliophyte (i.e. fully exposed to sunlight) gives a greater yield than when grown as usual under the shade of a tree cover.

In the wild, this shrub is a skiophyte adapted for life as a rainforest story shrub, but this adaptation to a low light intensity does not necessarily imply that it prefers shaded conditions.

And the practice of growing cocoa as a forest-edge crop, under the shade of the trees, frequently exacerbates the pest situation in that many of the more serious pests live on (or in) the forest trees and continually invade the crop plants from this vast natural reservoir.

In parts of Africa, the most serious pests to ripening cocoa are the local monkeys, and in the forest, these animals are almost impossible to control economically. In Europe, it has long been realized that strawberry plants grow and yield best when fully exposed to sunlight, even though they are found wild as woodland ground flora.

To minimize pest damage to agricultural crops it might be advantageous to review cultivation methods to determine that each crop is really being grown under optimum conditions, and not just to continue cultivation practices on the grounds of historical precedent.

3. Avoidance

Empirical observations will reveal that certain areas (and fields) are constantly ‘at risk’ from particular pests and conversely others are pest-free. Clearly, if a crop can be grown in areas of the latter category it can be expected to remain free from that particular pest.

This practice is particularly effective against certain soil-borne diseases and nematodes, but less so against most insects because of their greater mobility. This is one of the advantages of shifting cultivation, so widely practiced in parts of the tropics.

Soil insects, such as root maggots (Anthomyiidae), wireworms, chafer grubs, rootworms (USA), and swift moth caterpillars, can to some extent be avoided by the planting of non-susceptible crops and the growing of vulnerable crops at some distance away.

Such practice is to be highly recommended but is sometimes difficult to achieve as there may be strong agricultural, or other, reasons for growing the crops in those areas.

Thus in the UK, the East Anglian fenlands are ideal for growing carrots, celery, and parsnip, but many of these areas have endemic Carrot Fly populations on the native hemlock and other Umbelliferae and have long been areas highly ‘at risk’ from Carrot Fly.

In this situation, it is possible to minimize the risk from this pest by using other cultural methods such as crop rotation, etc., and of course, chemical protection has to be used.

4. Time of Sowing

By sowing early (or sometimes late) it may be possible to avoid the egg-laying period of a pest, or else the vulnerable stage in plant growth may have passed by the time the insect numbers have reached pest proportions.

Early sowing is regularly practiced against Cotton Lygus (Taylorilygus vosseleri) and Sorghum Midge (Contarinia sorghicola) in Africa. In N. Thailand it has been shown that early transplanting of paddy rice reduced the level of Rice Gall Midge attack appreciably.

Another important aspect of the time of sowing is that of simultaneous sowings of the same crop over a wider area, to avoid successive plantings which often permit the build-up of very large pest populations.

In Europe, the recent trend towards autumn-sowing cereals (winter wheat, winter barley) has reduced the risk of aphid damage to seedlings to a negligible level.

At the same time, this practice does increase the risk of Wheat Bulb Flies. Autumn-sown field beans are generally not at risk at all from Black Bean Aphids, whereas the spring-sown plants may be severely damaged.

With Wheat Bulb Fly only the very early-sown spring wheat is at risk, so if spring wheat is sown later there is little risk from this pest, but if sowing is delayed too much then crop growth is impaired!

5. Deep Sowing (Planting)

Some seeds are less liable to damage and pest attack if rooted deep, but of course, if planted too deep germination will be impaired. Many root crops are also less liable to attack by pests if they are deeper in the soil.

This is true for sweet potatoes in that the deeper tubers always have fewer weevils (Cylas spp.) boring inside, and the deeper potatoes have fewer infestations of Tuber Moth larvae.

Even if no special attempts at deeper planting of root crops are made, then care should be taken to ensure that no tubers are allowed to grow too close to the soil surface; earthing-up should be done when required. Exposed root crops may be damaged by pheasants, other birds, and rodents, and rabbits grazing.

6. Time of Harvesting

Prompt harvesting of maize and beans may prevent these crops from becoming infested by Maize Weevil (Sitophilus zeamais) and Bean Bruchid (Acanthoscelides obtectus) respectively.

Both of these pests infest the field crops from neighboring stores, but are generally not able to fly more than about half a mile, so an added precaution is to always grow these crops at least half a mile away from the nearest grain store.

New varieties of crops that mature early may enable a crop to be harvested early before pest damage is serious. This is one of the qualities that many plant breeders are constantly seeking in a very wide range of different crops.

This approach requires detailed knowledge of the ecology and life history of the local serious pests so that crop development might be desynchronized in relation to pest population development.

7. Close Season

In E. Africa legislation has been passed to ensure that there is a close season for cotton growing in order to prevent population build-up of Pink Bollworm (Pectinophora gossypiella) which is oligophagous on Malvaceae.

This legislation stresses that all cotton plants should be uprooted and destroyed (or burned) by a certain date and quite clearly no seed would be planted until the following rains arrive.

However, it is clear that many farmers do not bother to destroy the old plants by the appointed date and so in some areas, there is considerable survival of diapausing Pink

For bollworm larvae, this approach to pest control tends to be more applicable to the tropics where insect development and crop production may be more or less continuous.

In temperate regions, there is already established very firmly a close season for virtually all crops, namely winter!

8. Deep Ploughing

Many Lepidoptera (particularly Noctuidae, Hepialidae, Sphingidae, and Geometridae), Coleoptera, and Diptera pupate in the soil, and a large number of their larvae live there. The bulk of the soil insect population lies in the top 20 cm of the soil (most are in the top 10 cm).

Deep plowing will bring these insects to the surface, to be exposed to hot sunlight (insolation), desiccation, and predators.

In many tropical areas, a farmer plowing a field will be followed by a flock of cattle egrets, little egrets, crows, or starlings, in a seaside locality there might be a flock of gulls; all these birds will feed on the exposed worms, slugs and insects.

In temperate regions, a plow is usually accompanied by a large flock of birds (gulls, crows, etc.), and although the birds are also eating earthworms their consumption of insect larvae and pupae (many or most of which are pests) must be prodigious, as often a hundred or more birds may follow a single tractor.

9. Follow

Allowing a field to lie fallow almost invariably reduces pest and pathogen populations, but care must be taken to ensure that there are no volunteer crop plants or important secondary host weed species.

Following may be done as bare following when the soil surface is left bare, or flood following when the field is flooded with water for a while. Sometimes, as an alternative, a cover crop of legumes is grown as green manure which is then plowed under.

10. Crop Rotation

In olden times a period of fallow was an essential part of all crop rotations, but nowadays economic pressures mean that fields can seldom be left fallow.

Instead, basic crop rotation is usually practiced for the obvious reasons that continuous cultivation of one crop depletes the minerals and trace elements in the soil quite rapidly, and also induces disease and pest build-up.

However, some agricultural crops require rather specialized growing conditions, and these, combined with the practice of large-scale cultivation, result in some areas growing crops such as sugarcane, wheat, pineapple, maize, or potato, almost continuously.

Obviously, the orchard crops (apple, plum, pear, citrus, peach, olive, etc.) are also very long-term monocultures, as are vineyards. The alternation of completely different crops in a field has very obvious advantages from the pest and disease control aspects.

But in a rotation it is necessary to remove a particular crop quite a distance away; having the same crop in an adjacent field is not really ‘rotation’ so far as active insects are concerned, although it might be adequate for soil nematodes and some soil-borne diseases.

So, for effective pest control crop rotation has to separate crops both spatially and in time (temporally).

Against monophagous and oligophagous pests crop rotation can be effective, especially with beetle larvae that may take a year or more to develop, but it is not effective against migratory pests or those with effective powers of dispersal.

The alternation of cereals with non-cereals may be an important method of curtailing Nematocerus weevils in Africa.

A common type of rotation is the alternation of a legume crop with cereals; this is effective against some pests, but others (e.g. Colaspis, Diabrotica) can utilize both host types. In Europe, a combination of potato, wheat, and rape is currently popular and successful.

11. Secondary Hosts

Most pests are not monophagous and so will live on other plants in addition to the crop. Sometimes, in point of fact, the crop itself is not the preferred host! For example, Turnip Aphid is often more abundant in Cardamine and charlock, etc., than in the Brassica plants.

In many cases, the pests build up their numbers on wild hosts and then invade the crop when the plants are at the appropriate stage of development.

Many Cicadellidae and Delphacidae that are crop pests (on rice and other cereals) feed and breed on wild grasses in the vicinity of the paddy fields so that when the young rice is planted out there is a large bug population waiting to infest the young tender shoots of the rice.

The destruction of alternative hosts (or the control of insects on them) may be an important part of an IPM program. The alternative hosts are usually native plants (but may be introduced), and maybe trees, shrubs, or herbaceous plants; they may be cultivated species, wild plants, or weeds.

Solanaceous weeds, for example, are important alternative hosts for pests of tomato, tobacco, eggplant, and potato.

In many cases the permanent pest population in an area is maintained not on crop plants but on wild plants belonging to the same family; there are many wild Cruciferae that support Brassica pests and the number of wild Leguminosae, Chenopodiaceae, Rosaceae, etc., is very large.

In temperate situations a number of pests and diseases have an alternation of generations on quite different hosts, e.g. Myzus persicae on peach and potato. The removal of the alternative host can effectively reduce such pests to insignificance, but in the case cited, of course, the alternative host is itself a crop plant.

Black Bean Aphid overwinters on spindle trees, and in some areas attempts have been made to remove these trees locally, but usually without much success. Pemphigus bursarius overwinters on poplar trees where it makes petiole galls in the spring; later generations migrate to lettuce where they encrust the roots.

With monophagous pests, it is important to remove any host plants between crops (if feasible for the species concerned). A monophagous insect would normally be confined to the species of a single genus for the host, though it would be unusual for it to be restricted to a single species of one genus.

Thus, for sugar beet pests it is not feasible to attempt to remove all wild species of Chenopodiaceae as they are too abundant. But, for the Brown Plant hopper of Rice (Nilaparvata lugens) which is restricted to rice (Oryza spp.) as a host plant, the alternative host plants are either wild rice or volunteer rice; by the destruction of wild rice weeds, volunteer plants, and crop residues, this pest can be partially controlled.

The situation with regard to secondary/alternative hosts tends to be more important in the tropics where usually there are more wild plants in the immediate neighborhood of the crop, especially where land is cultivated along the edges of tracts of native forest (‘jungle’).

12. Weeds

Most cultivation practices require the destruction of weeds because of their competition with the crop plants, and their interference with different aspects of cultivation. But weeds can also be important from the viewpoint of pests and diseases; sometimes the weeds may be alternative hosts, as already mentioned.

Weeds in a particular crop often belong to the same family as the crop plant because of the selective nature of many post-emergence herbicides.

Some pests seem to prefer weeds as oviposition sites; for example, some cutworms (Agrotis spp.) and some beetles (Scarabaeidae) lay most of their eggs on, or in the immediate vicinity of, weeds in the crop.

Weed removal at the appropriate time may result in many potential pests being destroyed. Some weeds are important as natural reservoirs (alternative hosts) of both pathogens and invertebrate pests.

13. Trap crops

The use of trap plants to reduce pest infestation of various crops is based upon the knowledge that many pests actually prefer feeding upon plants other than those on which they are the most serious pests.

This preference may be exploited in two different ways: either the pests are just lured from the crop onto the trap plants where they stay and feed, or else, because of the greater concentration of pests on the trap plants, only the trap plants need to be sprayed with pesticides.

In the latter case, since the trap plants are either grown as a peripheral band or else inter-planted at about every fifth to the tenth row, the saving of insecticide represented is considerable.

This is a technique used mostly in warmer parts of the world where insect pest breeding is more or less continuous; in the cooler temperate regions, with the cold dormant winter period, it is of less applicability.

The practice of intercropping is based upon the same premise, and this has long been a regular method of reducing levels of pest damage.

14. Intercropping

This practice obviously has various drawbacks for large-scale agriculture, but can be of particular application for small farmers, who often use little insecticide. Intercropping can certainly reduce a pest population on a crop, and without a doubt, reduces the visual and olfactory stimuli that attract insects to a particular crop species.

As a method of control, it is most effective against exogenous pests, such as locusts, which enter the crop for only part of their life cycle. Groundnuts are inter-cropped with maize, and nymphs of Locusts were induced to leave the maize (particularly on hot days) for the lower foliage of the groundnuts where they were eaten by ducks.

On smallholdings, it has long been a regular practice to intercrop, often using plants with very strong odoriferous qualities in the hope that the odors released would confuse the host-seeking female insects, which it does appear to do.

Onions and crucifers, for example, would be used to shield carrot crops. Often wild type plums are grown around the periphery of apple orchards where they act partly as a windshield and also as a diversion for a number of different insect pests.

15. Crop sanitation

This is a rather general term and usually is used to include the following different aspects of crop cultivation;

Destruction of diseased or badly damaged plants – the roguing of such plants is an important agricultural practice, but of course, requires hand labor.

For agricultural crops, this is sometimes not feasible, but some farmers do make the necessary effort; with horticultural crops such as fruit orchards, flowers, and some vegetables, destruction (preferably by burning) of infected and infested branches, etc., is an important aspect of any control program, as it is easier to remove the foci of infection than to kill the organism with pesticides.

Removal and destruction of rubbish – old crop remnants, fallen leaves, branches, dead trunks, also weeds, etc. Some pests use rubbish heaps for breeding purposes, for example, scarab larvae are to be found in rotting vegetation and soil, especially in rubbish heaps.

The tropical Oryctes beetles are good examples, as the larvae are found in rotting palm trunks and rubbish heaps.

Removal and destruction of fallen fruits – for the control of many fruit flies and boring caterpillars this is important, as the insects will continue to develop in the fallen fruit and will pupate either there or in the soil.

This is, in fact, still a successful method for reducing the numbers of Codling Moth and other fruit-boring caterpillars, as well as for many different fruit flies (Tephritidae). It is still one of the best methods of control for Coffee Berry Borer, where labor permits.

Destruction of crop residues – this is often vitally important in order to kill the resting stages (pupae, etc.) of many pests after harvest.

Many stalk borers (Pyralidae, Noctuidae) pupate in the lower parts of the cereal stems and as such will be left in the stubble even if the main parts of the stalks are removed. With some crops of maize, sorghum, and millet most of the actual stem is left.

The stems should be burnt immediately after harvest. The rotting residues of crops such as turnip, parsnip, and Brassica generally, after being plowed in attract ovipositing female Bean Seed Fly and other Muscoidea.

For diseases, crop residue destruction maybe even more important. Plowing in crop stubble may kill a small proportion of pupae but most will survive; burning is most effective.

European corn borer traditionally overwinters in maize stubble, but most farmers are now aware of this and so the stubble is destroyed. The recommended method of destruction of all weeds, crop residues, rubbish, rogued plants, fallen fruits, etc., is by collection and burning; other methods may not kill the pests.

Crop sanitation tends to be a term mostly used by plant pathologists rather than entomologists, as it aims mostly at the removal of sources (foci) of disease infection.

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