On the small farm, or in the home garden, techniques suitable for the production of food might be quite different from those used in large-scale production systems. The use of machinery, for example, might be impossible or uneconomical, or special small-scale equipment might be needed. The wide variety of crops produced implies that the production schedule will be complex. Chemical treatments designed for one crop are liable to interfere with another. Furthermore, the farmer or gardener often will not have the same depth of experience as the large scale commercial farmer, and in the interest of safety may wish to avoid certain substances or machinery. In addition, small scale production may not be plagued with the problems common to large scale production or the farmers may choose to accept a certain reduction in yield or price or a decrease in attractiveness in order to avoid pesticides.
Nevertheless, the small farm or home garden is likely to experience a wide variety of problems, especially with weeds, insects, and diseases, The techniques for dealing with these problems are extremely varied. There is little hope that the small farmer can discover these only through his own experience. Therefore, in this bulletin, different techniques are discussed in order to give the small operator a background of information which can serve as a general guide. We emphasize, however, that small-scale production is an art learned by experience. Therefore, in this bulletin, different techniques are discussed in order to give the small operator a background of information which can serve as a general guide. We emphasize, however, that small-scale production is an art learned by experience. There are no final answers nor perfect recommendations.
The same conditions that favor the growth of crop plants also favor the growth of weeds. While diseases and insects are neither always present nor important in the garden or small farm, weeds invariably accompany any planting. If not controlled, these unwanted plants rob the fertility of the soil and impede normal growth of crop plants. Weeds can be considered the number one pest on the small farm. To control them will always be difficult. To leave them uncontrolled will be even more costly in the long run.
Weeds are highly competitive plants that are stimulated by the opportunities man offers through his disruptions of the environment. As a rule, when man disturbs the soil, weeds follow. Agricultural activities provide opportunities for weed growth, and. indeed, many weeds owe their survival to farming activities. The ideal situation for the farmer is not necessarily the elimination of weeds, but their control, so that they do not interfere with the growth of crops. Weeds do serve some useful purposes, including protection of disturbed land from erosion, feed for wild and domestic animals, and even food for human use. Furthermore, except in specific limited situations, complete elimination of weeds is very difficult. The control of weeds begins with an understanding of their characteristics.
Because weeds are so varied, from plants that float on water, to parasites that live only on other plants, from rapidly maturing annuals, to perennials growing in forests, the strategy of control will vary. Techniques that are suitable for one may not be for another. In the garden or small farm, understanding of weed biology proceeds the selection of the technique that can be used. Simple observation of weeds and their characteristics provide the clues to effective control.
Some possible characteristics to keep in mind are annual versus perennial nature, ability to reroot if cut and left on the ground, ability to reshoot if crowns or roots are left on the soil, rapidity of growth, and number of seeds produced, ability of seeds to remain dormant for long periods in the soil, methods of propagation and distribution, and suitability as animal feed.
When efforts are made to remove weeds in general, a reaction may be started. As one kind of weed is removed, another may take its place, and a new technique for its control might be necessary. Therefore, weed control is not simple. It is an art that each gardener or small farmer should master.
Physical removal of weeds
An old, effective, and simple technique for weed control is actual removal of the unwanted plant. This might be done by pulling up the plant by hand, root and all, and leaving it to dry out where it cannot root again. If the weed cannot be pulled out, it might be possible to dig it out or to cut it just below the level of the soil with cutlass, machete, or hoe, so that the shoot and the crown are removed. The use of a hand-pushed machine or animal, or drawn cultivator, are really only mechanical extensions of the hand hoe and may be more rapid, but frequently do an inferior job.
Physical removal of weeds is a good technique, but usually a very costly one. The removal of weeds by hand in a vegetable garden may be the biggest chore in the production system. Furthermore, the techniques for removal are not perfect. When hand pulling weeds, little weeds are invariably left behind and these soon become big weeds. The technique is very inefficient. When plantings are weeded with a hoe there is danger that crop plants will also be eliminated. Some weeds are almost always left behind very close to the crop plants, and it might be desirable to remove these by hand. Cultivation is often effective if crop plants are in straight lines. The cultivator can cut the weeds between rows and simultaneously throw a small amount of soil towards the crop plants, thus covering the young weeds with soil and smothering many of them. Physical removal of weeds by any technique can expose buried weed seeds to light and air, and thus stimulate their germination. Physical removal will continue to be a valuable weed control technique, but often better techniques will be available
Reduction of vigor of weeds
Any technique that reduces the vigor of weeds without simultaneously reducing the vigor of crop plants is a useful weed control measure.
Techniques are highly varied. A sharp cutlass is a rapid and useful instrument for reducing the height and vigor of weeds, although it will seldom kill them. This technique is most effective where weeds
are abundant and succulent. It is more difficult with tough, lignified stems of old grasses or with woody weeds. If seeds have already formed, it is advisable to remove the weeds to avoid reseeding; otherwise, cut weeds can be left on the ground and may serve as a mulch to shade out and impede further weed growth. The dead weeds sometimes can be burned, which might destroy their seeds, and can weaken or destroy parts not eliminated by cutting.
Mulching is frequently an effective technique for reducing weed growth. A variety of materials can be used to cover the ground and thus provide poor growing conditions for weeds. Materials such as plant residues, straw, sawdust, seaweeds, newspapers, plastics, gravel, industrial wastes, old planks; and even stones have been used effectively for this purpose. Mulching may reduce weeds by keeping seeds from sprouting, shading seedlings, smothering plants, or providing them with damp or adverse growing conditions. A very good time to apply mulch is after crop plants are well established, but while weeds are small.
Mulching has its disadvantages. Mulches may provide shelter for pests, including slugs, snails, insects, and even rats that emerge during the night to attack crop plants. Mulching may retain too much humidity, which provides ideal conditions for some plant diseases. Mulches of some materials, such as sawdust or straw, rich in carbon, but low in nitrogen, may compete with crop plants for nitrogen that is used by microorganisms in decomposing the mulch. Finally, some mulches such as gravel, stones, plastics, and planks might be difficult to remove when the soil is prepared for replanting.
Flooding is a specialized measure for control of weeds in some tropical crops. To flood requires flat areas and a water supply so that water can be added or removed at will. Flooding is most effective when the crop involved is either tolerant of flooding or requires high amounts of water (rice, taro, kangkong, water lotus). In some cases flooding can be combined with nitrogen fixation by blue green algae, a common feature in rice paddies, or in combination with a small fern, an introduced plant in Southeast Asia from China. Alternate flooding and drying might be useful to reduce weed seed populations in small plots. Almost all soils can be flooded, but a few soils will allow water to seep out continuously, and thus might be impossible to flood.
Flooding works best for soils with an underlying impermeable layer. This not only impedes loss of water, but also loss of nutrients by leaching. Flooding and draining might leave some soils less fertile than before, in other cases it can be used to dissolve and remove excess salts. Flooding, while reducing the growth of or killing many weeds, will stimulate the growth of a few others. Therefore, it is a very specialized technique, sometimes very useful, and sometimes not at all.
Shading of weeds is a useful weed control method. Shading is most effective when weeds are small. To accomplish adequate shading, it is desirable to promote rapid growth of crop plants so that all or almost all of the sunlight is intercepted by the crop plant (or the shade-giving shelter or device). Shading might not be effective with some vines that are stimulated to elongate and grow through the crop plants to obtain sunlight. Shading-out of weeds works better with tall crop plants than with short plants.
Cover cropping is an effective weed control measure that provides some of the features of mulching and shading, and in addition weakens the weeds by competition. A good cover crop must be vigorous but not. weedy; it should be controllable; it is very desirable that it be a soil building crop, which adds organic material and nitrogen to the soil. Some annual legumes including the velvet bean (Stizolobium deeringianum) and some vining cowpeas (Vigna unguiculata) fulfill these requirements for the tropics.
They can be grown rapidly from seed and can be easily destroyed when necessary. They produce seeds in abundance for replanting, but their seeds do not persist if left on, or buried in the soil. Velvet beans should prove extremely useful in tropical cropping systems not only for weed control, but also as a nitrogen source and a soil building material.
Fire is a controversial weed control measure. Fire is useful in removing excess quantities of wood or old lignified grasses or for killing grass seed rapidly. Fire will deposit some minerals on the soil from the vegetative material burned, although part of the mineral is lost in smoke, or might be lost later by runoff of rainwater. Fire is often an effective tool in reducing disease or insect infestations. Fire will change the nature of the plant population on a piece of land. It might be very useful for renewing pastures.
On the other hand, fire is difficult to control and can damage valuable forests, plantings, or structures. Fire can destroy material that could be useful for mulching or for soil building. Fire can kill useful insects, birds, and other small animals. It exposes the soil to the sun and can result in destructive changes, such as hardening of lateritic soils and soil erosion. Therefore, fire is a controversial weed control technique.
Interruption of life cycle
As a weed control measure the interruption of life cycle involves various techniques previously mentioned and some still to be mentioned. A common technique is the plowing of ground before planting. Plowing accomplishes many purposes; the breaking up of compacted soil to permit better penetration of water and growth of root systems, the aeration of the soil, and exposure to the sun which kills some insects and nematodes, and the burying of living weeds and dead organic material so that decomposition will occur. Plowing leads to rapid changes in weed populations, however, and rapidly growing, very seedy weeds are soon likely to predominate in plowed fields.
Plowing can promote serious soil erosion on slopes or in areas of intense rains or high winds. So called non-tillage methods, designed principally to reduce soil erosion, generally rely on chemical sprays to control weeds, and might avoid the vicious cycle of annual weed production in plowed fields.
The removal of weeds before seeding is an effective technique to reduce weed populations gradually in small gardens and to arrive at an essentially weed-free situation. To be effective, such control must be combined with techniques to reduce introduction of weeds to the area. Such techniques include barrier strips or crops, use of composted (seed-free) vegetable material, use of seedless mulches, and use of screens in irrigating systems to avoid distribution of weed seeds. On the small farm neglect of the field after harvest is a certain way to increase weed seeds for the following year. Whenever feasible, techniques to interrupt the cycle of seedings should be practiced, including plowing and grazing.
Use of animals as weeders
Animals can effectively control weeds in some situations. In a very weedy area introduction of cattle to physically beat down the foliage can be a work-saving beginning for weed control. However, a more effective technique is to graze animals on the area. Each species of animal has its advantages and disadvantages as a weed control agent, but some generalities are also useful. Grazing as a weed control method is most effective when it is severe, but even with this, some supplemental weed control might be necessary.
Grazing is most effective when weeds are young. Animals must be carefully limited by fences, or staked with ropes or chains, so that they graze only where they are wanted. Grazing may not be sufficient to fulfill the animals nutritional requirements.
Cattle are quite effective in removing weeds if they are confined to a small area. They prefer grasses but will eat a wide range of weeds, Continued use of a small piece of ground can compact the soil and make planting difficult. The use of cattle should be followed by other methods such as manual or mechanical cutting to destroy ungrazed or ungrazable species.
Goats are poor weeders unless they are confined to small areas. They will eat a broad range of seeds including seeds of some noxious weeds, but they prefer frequent changes in diet. They tend to eat the young and tender tips of many species, but often avoid the tougher parts of plants unless very hungry. On the other hand, goats will eat and destroy some favored shrubby species. Goats used for milk production should not be overly forced to eat weeds or milk production will fall, but meat producing and male goats can be forced to eat weeds.
In some instances sheep may be the most effective weeders. They have wide appetites and the ability to sever weeds very close to the ground. This should be carefully managed so they do not promote soil erosion.
Pigs are useful in small areas because of their habits of searching for edible roots. They can be used to clear the weeds from a garden patch, loosening and fertilizing the soil as well. Rotating a garden with a pig yard is a low labor technique of considerable value, and can be extended to larger plots if the pig density is sufficient to eliminate the weeds.
Chickens will destroy most weeds. The most efficient way to use them is in a mobile cage that can be lifted or pulled along the ground. If chickens run free they will eat what they please and destroy ornamental and food plants as well.
Ducks and geese are good at eliminating weeds. In a pasturing cage, however, they will dirty the entire area long before they can remove all the weeds. They can be used most efficiently in orchards where they can keep the ground free of weeds without damaging the trees. Chinese geese are the best as they will systematically clear out grass, but neglect broad-leafed plants, except for the young and tender.
An unusual weeder is the guinea pig, primarily a grass feeder that can be raised on grass alone in a pasturing cage with net bottom. Guinea pigs can be useful in the small garden for cleaning out weeds around shrubs in inaccessible places. They must be confined with a short fence (or a tall fence if dogs and cats are around). They will burrow, and must therefore be watched so that they don't escape.
While the use of animals as weeders is not a widespread practice, judicious use is advocated, for animals can perform a useful service; removal of undesired vegetation, adding of manure to the soil, and yielding milk, eggs, or meat.
Chemical control of weeds
In some cases chemical control of weeds might be the most efficient and even the least expensive method of weed control in the garden or on the small farm. Weed control chemicals are like arms in an arsenal, waiting to be used and available in different "calibers" for different purposes. Like all arms, they are potentially dangerous and must be used with foresight and knowledge. Some have residual effects, that is, they can kill crops planted later on, All can kill desirable plants as well as weeds when used improperly. Others are poisonous to mammals. Apart from these disadvantages, chemical weed killers must be purchased, as well as equipment to apply
them. The cost of looking for them, purchasing, transporting, and storing them and the maintenance of equipment must be weighed against the benefits obtained from their use.
Weed killers are of a number of types with respect to specificity and mode of action. Not all kinds will be discussed here. A contact herbicide kills only those parts of the plants touched by the substance. A sterilant is usually applied to the soil and kills all the plants that absorb it. A systemic herbicide is usually applied to the foliage (but may be applied to the soil) and is translocated to vital parts of the plant, causing its death. A selective herbicide kills some kinds of plants but does not kill others. A selective pre-emergence herbicide is applied to the soil before the crop or weeds emerge and kills the weeds as they germinate or soon thereafter, but does not damage the crop plant.
Chemical weed killers must be used with greater care in the home garden or small farm where a great variety of crops are cultivated together or in sequence. Many herbicides can severely retard growth and development of sensitive plants from six months to a year after being applied to the soil. Thus, great care in the choice of herbicide or the crop combination must be exercised, and it is suggested that other methods described in this paper may often be more appropriate except where special problems justify their use.
Table 1 lists some commonly used herbicides that might be used in the home garden or small farm. Common name with trade name is given, along with method of application, crops in which it is used, type of weeds controlled, and precautions which should be observed.
Before using herbicides advice should be obtained for the specific condition under which they will be used. Two herbicides merit special consideration here. Paraquat is a non-selective contact herbicide, killing only those green parts of the plant it makes direct contact with. Thus, it is sometimes likened to a "chemical pruning". Perennial plants and annuals with considerable development, and with growing points which are protected from direct contact with paraquat, will regrow after 10-20 days of desiccation of existing foliage. Thus, annual grasses such as Digitaria often recover from an application of paraquat if they have reached 60 to 70 cm in height.
Paraquat is widely used to kill young weeds in established crops, using a protective shield to avoid contact with the crop. This method is five to ten times faster than hand weeding in many cases, and as little as one liter/ha is adequate, thus resulting in considerable economic savings in many cases. Paraquat presents the additional advantage of being inactive in nearly all soils. Thus, it is frequently applied to standing weeds and the following day the weeds will be desiccated and planting can be done without any effect on germinating seeds. This is frequently done in no-tillage systems.
Great care should be exercised, however, when using this product. Rubber gloves, a simple respirator, and goggles should be worn as paraquat is very toxic (fatal) if relative small quantities of the concentrated product is inhaled or swallowed. Contact in the eye could cause blindness if not washed out immediately. Burning and blistering will result from direct spills on the skin if not washed off. Contaminated clothing should be removed immediately to avoid burns, blistering and absorption into the body. The skin toxicity is less when mixed in a normal spray solution, but precaution should always be used.
Glyphosate is a translocated, non-selective herbicide, killing most plants 4 to 15 days after its application. Its action is faster with warm temperatures than under cold temperatures. This product needs only contact a limited portion of green foliage to be absorbed and transported throughout the plant to bring about its death. It is particularly effective against numerous perennial grasses and can
bring about their eradication with repeated use. As paraquat, glyphosate is practically inactive in the soil. It has the further advantage of having a relatively low toxicity to mammals. One of its most common uses is in non-tillage systems, or in application to standing weeds some 510 days before planting. Its application should be followed by 67 hours without rainfall for best results.
The art of weed control
The control of weeds can never be a perfectly accomplished task. It is difficult to give exact rules because situations vary so widely. Therefore, knowledge and experience with a wide variety of techniques is desirable. From this comes judgment, the ability to choose a good technique for the weed control job necessary. Then, weed control is an art. Some people will do the job better than others. But, of course, this is true of agriculture in general. To do a good job requires knowledge and experience, as well as good judgment, timely attention, and personal dedication.
SOME COMMONLY USED HERBICIDES THAT MIGHT BE OF USE IN THE HOME GARDEN OR ON THE SMALL FARM
Method of application
Type of weeds
Naptalam (Alanap L)
Preemergence (liquid, sprayed)
Cantalope, cucumbers, peanuts, watermelon, soybeans
Many annual broadleaf and grass weeds
Dinoseb (Dinitro3, Dynamyte 5, Premerge 3)
Preemergence or post emergence (liquid, sprayed)
Beans, field corn, sweet corn, popcorn, peanuts, potatoes, onions, peas, cucumbers, pumpkins, squash, watermelons
Mustards, annual smartweed, nightshades, and many other annual hroadleaf and grass weeds
|Do not use on sandy soils. High toxicity to table for specific products. See use if temperatures will surpass 95° after application.|
Linuron (Lorox, Afalon)
Preemergence (powder, sprayed)
Carrots, celery, corn, potatoes, soybeans, sorghum
Most annual broadleaf and grass weeds
|Do not plant sensative crops within 4 months.|
Bensulfide (Prefar 4E)
Preplant incorporation, preemergence (liquid, sprayed)
Cantalope, carrots, cole crops, cucumbers, lettuce, onions, peppers, tomatoes, watermelon
Most annual grasses, some broadleaf weeds
|Incorporate into soil if irrigation or rainfall do not follow application. Very persistant. Do not plant non-labeled crops for 18 months.|
Apply to foliage of weeds
Prior to planting of most crops
Most annual and perennial weeds, especially grasses
|Will kill most crop plants, great care must be used to avoid contact with crops.|
In the small agricultural operation, there will always be problems due to insects and other pests. These are part of the environment, exist as numerous species, and stand ever ready to move onto crops in search of their own livelihood. When insects damage crops they can be thought of as an undesirable part of the environment. The problem is then to tolerate them or to control them without damaging other aspects of the environment.
It is often impractical or even impossible to eliminate insect pests. The use of chemical insecticides on a small scale is associated with many hazards: the danger of killing beneficial insects, of contaminating other plants, the short and long term poisoning of human beings, the problem of storage of poisons around the house. The damage done may outweigh the benefits realized. Therefore, we advise the use of chemical insecticides in the small planting only as a last resort.
If we were to attempt to recommend chemical controls, we would face a bewildering complexity of experimental results and recommendations. Regardless of the point of view of the farmer, concerning chemical pesticides, we recommend that they be used always with great care.
Therefore, in order to reap something from his efforts the farmer must seek other alternatives. These should be practical, simple, efficient, economical, and should not create new problems. Since such approaches have seldom been investigated by agricultural scientists, recommendations given now must necessarily be based on simple observations. Nevertheless, a considerable body of experience lies behind recommendations.
In a certain sense, small-scale agricultural production is like a war consisting of numerous battles. Some of the battles are won, and some are lost. The beginner may lose more battles than he wins. Later, as experience is gained, a progressively larger number of battles will be won. These principles are written with the hope that the farmer will begin to win battles sooner due to what he has learned here.
Pre-planting prevention and post-planting care
Control of insects begins before planting. Removal of old living and dead material from the site, and of weeds and trash from the surrounding area, eliminates places that insects and other pests can hide. Plant materials that are apparently free of insects and disease can be placed in the compost pile, but infected plant materials should be burned.
The composition of the soil will affect the pest population. Nematodes thrive in sandy soils. Clay mils make possible permanent burrows of some cutworms. A loamy, friable soil, kept in good condition by frequent addition of compost, is a better alternative. A rich, organic soil, with its many forms of living organisms, discourages the buildup or dominance of any one pest, and often is, in itself, a control measure. Cultivation of the soil is sometimes useful in pest control. Insect eggs and pupae are often disrupted and destroyed. Nematodes are reduced by exposure to air and sun. When possible, pre- planting cultivation should be repeated just before planting. After planting, cultivation should be continued for various reasons, such as pest and weed control, but should be shallow to avoid damage to roots of the plants.
A critical stage in farming is the germination of the seed and the establishment of the seedling. Pests and disease can nullify careful efforts rapidly during this stage. Therefore, certain practices are desirable. Seed should be fresh and of high percentage germination. It should be free of visible insects or disease. Large seeds may attract rats that dig and eat them. This can be reduced by soaking the seed overnight in water and planting the next morning. In small operations, as seedlings emerge they can be protected at night by placing a can or bottle over the plant, and if birds are a problem during the day, by covering the plant with an open-ended can and perhaps a screen. Seedlings are often destroyed by very small insects, but this is sometimes avoidable by not over-watering seedlings.
We recommend that when possible seedlings be established before planting in special containers filled with soil sterilized in the oven. These containers can be peat pots or homemade paper pots that disintegrate in the soil, or they can be conventional pots. Seedlings should be started in a small insect- free greenhouse protected from insects by fine screen. Seedlings should receive full sun as soon as they germinate, but of course they should not be allowed to dry out. When seedlings are 8-10 cm in height, they should be transplanted to the previously prepared bed, where further protection may then be necessary. Careful attention to the establishment of seedlings is one of the most important factors in good farming.
The use of mulches is a very controversial aspect of insect control. Mulches placed on the soil may actually provide hiding places for insect pests. Therefore, mulches should be occasionally inspected, especially if damage from cutting insects is observed. Mulches that reflect light, such as aluminum foil and some plastics confuse aphids and reduce their attacks. Orange plastic mulch discourages insects in general. Mulches can be expensive or costly in terms of labor. They do not relieve all problems, and thus should be tried with some reservation.
An important cultural practice in insect control is rotation of plantings. If the same crop is planted time after time in the same site, the opportunity is present for multiplication of pest and disease organisms in the soil. Rotation reduces the probability of such buildups, but cannot eliminate the possibility. It is well known that certain plants encourage pests while others discourage them. Since it is practically impossible to give exact instructions for the many situations found in the small planting, it perhaps is more useful to know a few general principles that can always be applied. Never plant the same crop in the same site without use of another crop first. In rotating, avoid using the crops of the same family in succession on the same soil. The principal families of vegetables are the legumes, the solanaceous vegetables (tomato, pepper, eggplant), and the cucurbits (squashes, pumpkins, cucumbers, melon).
Use of pest-resistant varieties
Perhaps the most effective solution to the problem of insects in the small planting is to use varieties that are resistant to them. Resistance depends on many factors, but species with strong odors or with very pubescent leaves are
Often insect resistant. On the other hand, the odors of the Brassica vegetables, cabbage and its relatives, seem to attract the insect pests that are especially troublesome with these crops. Thus, odor and pubescence are hints of resistance, but only practical experience over several years in one location can demonstrate truly resistant varieties.
A common form of resistance to insects and disease is rapid growth, very susceptible varieties of vegetables can be grown to maturity under ideal conditions before insects become a problem. This is particularly true of annual green leafed vegetables, especially Amaranthus. Successive plantings of these vegetables should not overlap, lest insects multiply on one generation and then attack another.
Resistance of a vegetable variety to insects and disease is often known and reported in seed catalogs. On the other hand, resistant species and varieties can often be discovered by observing what other people grow successfully. In any locality, many resistant varieties remain to be introduced and tested in order to discover their values.
Apparent resistance of vegetables to insect pests in the small planting may be only a chance phenomenon. When susceptible varieties are grown on a small scale, insect pests may not discover them on time to damage them. Thus, it is common in the small garden to experience several successful crops of a given variety followed by one or more failures. The avid farmer will learn from his mistakes, and will hopefully discover truly resistant varieties. If not, other methods of insect control can still save the crop.
Protection of one species by another
Insects and other pests use a variety of stimuli to find their way to suitable host plants. These stimuli include those affecting the vision, the sense of smell, and the taste. If insects can be confused, they often will not become a problem. We have already mentioned how mulches of various colors confuse insects. In addition, plants themselves protect one another from insect attack.
The first type of protection might be called passive. When any two plants of different types are placed side by side the odor and appearance of one will tend to distract from the odor and appearance of another. On the other hand, large numbers of plants of the same type planted together produce an effective odor and appearance that attracts readily the pests of that crop if they are near. Therefore, dispersing plantings of crops, or mixing them with other crops will reduce insect infestation.
In addition to the passive effects, plants can have general effects on insect pests, and repel indiscriminately many kinds of insects. This is generally due to the strong odors of such plants. The French marigold, Tagetas, is one of the most useful species in this respect. The best varieties are the old-fashioned ones with the strongest smells. Nasturtiums are also useful, and their leaves can be used as a cooked or salad vegetable. Garlic and onions are also effective. In the tropics, rows of bunching onions or individual plants can be interspersed with insect-sensitive vegetables. The space is not wasted, for the leaves of the bunching onions are used like those of chives. Herbs which are useful in the kitchen can be planted around or within the garden. The "Oreganos" of the tropics and basil are particularly effective. Mints of all varieties repel some insects. Peppermint is said to repel rats. Study is needed in the tropics to identify the best species of plants to use as general repellants, and the best way of utilizing them in the garden. But in the meanwhile, use can be made of those already available. We recommend, that whenever possible, plants that are selected as repellents be also plants that are edible in one form or another, thus economizing space while affecting control.
There is still a third form of protection of one plant by another that is frequently called "companion planting". The terms might be objectionable, for plants can hardly be companions to each other in the same sense that persons are companions. Nevertheless, it is true that two species of plants can be very effective planted together due to many different kinds of effects, such as light shading of one by the other, or fixation of nitrogen by one that is then used by the other. Although many cases are known of combinations of plants that grow better together than separated, the reasons for such success are frequently not known. In a few cases it is known that one species has the specific effect of repelling a pest of another. This specific effect is not the same as the general effect due to the strong odor of one species repelling insects in general.
Specific combinations of plants that mutually aid one another have seldom been studied seriously in the tropics, especially with respect to vegetables and small gardens. Thus, exact rules cannot be supplied to gardeners, but the following principles are appropriate: Plant vegetables in combinations and observe the effects. Develop a body of experience based on such observations. Plant harmonious
combinations where vegetable yields are high and pests are at a minimum. Thus, the gardener himself will develop a body of useful experience.
A few suggestions taken from experience in the temperate zones are given here below. These have not been tried experimentally in the tropics.
Combination of plants that are mutually beneficial:
- Asparagus tomatoes
- Beans carrots, corn, potatoes
- Beets bush beans, cabbage, lettuce, onions Cabbage (and relatives), beets, herbs, tomatoes Carrots chives, leaf lettuce, leeks, radishes Corn potatoes, beans, cucurbits, pumpkins Cucumbers cabbage, radish, sunflower Eggplant beans
- Lettuce beets, cabbage, strawberry Potatoes beans, cabbage, corn Pumpkins corn .
- Squash nasturtium Tomatoes asparagus, parsley
In addition, a few general suggestions of plants that are suspected of being useful to repel specific insects are given below:
|Insect or pest||Plant that protects from it|
|Aphid||Garlic, mint, nasturtium|
|Cabbage butterfly||Herbs, Mint|
|Colorado potato beetle||Bean, eggplant|
|Flea beetle||Mint, herbs, tomatoes|
|Mexican bean beetle||Nasturtium|
|Squash vine borer||Strong herbs|
The interrelationships of living organisms are very complex, and it is common to find one kind of organism living on another. To describe the situation when harmful insects and pests are destroyed by harmless or beneficial organisms the term biological control has bean used. Biological controls are natural processes adapted to the service of the farmer or gardener. They are often inexpensive and are usually appropriate and preferred to chemical controls. They are seldom one hundred percent effective, but neither are chemical controls.
One of the simplest controls in the small tropical planting is the presence of lizards and toads. These are often common or abundant. Their presence in the planting is a constant assurance that help is available. The lizards are active during the day, and the toads during the night. Lizards and toads can be encouraged by providing them with places to hide. For the lizards, cracks and crevices are important. Toads like damp places under stones or boards where they can hide during the day. A few concrete blocks or boards left at random through the planting can provide shelter. If lizards and toads are not already available, they can be caught and released in the planting. Some lizards will also eat seedlings and flowers of vegetables, so caution is needed.
Some birds are useful in the control of insects, and can be attracted by water, food, and nesting areas so that they are always nearby and alert for insect pests. Since the tropics is so varied with respect to bird species, local knowledge of the useful birds is necessary, together with careful observations to see that birds attracted to the garden eat insects and nothing else.
Other biological controls include the use of the bacterium, Bacillus thuringiensis, a disease effective against the larva of many kinds of moths and butterflies. It comes as a commercial powder and can be used as a dust or spray. When caterpillars are particularly prevalent, living and dead ones can be ground with water in a household blender and sprayed on affected plants. Apparently bacteria or fungi, always present, multiply and are effective in killing previously healthy caterpillars.
For the small planting, most biological control is passive, however, and consists of not destroying insects with chemical sprays. Insect infestations tend to run their course. A particular infestation will build up until natural predators become aware of it and begin to deal with it. Sometimes disastrous damage is done; sometimes new growth is rapid and insect free.
Where it is possible to buy lady beetles, these are very useful in the control of aphids and other soft- bodied insects.
Useful insects that should not be destroyed include dragonflies and damselflies, aphid lions, doodlebugs, mantids, and walking sticks. Spiders are also useful in the planting, and most are not harmful. Wasps of several types are useful. The mud daubers that live in protected locations of the house kill spiders and insects. Sometimes they do more harm than good. Some relatively small insects are powerful allies in the planting, tiny wasps, for example, the syrphid flies, and several kinds of egg parasites. Most of the beneficial insects are destroyed indiscriminately by poison dusts and sprays.
Much study of useful insects is necessary in the tropics, and, unfortunately, generalizations are not always helpful, for insect and pest problems vary with location and from place to place in the tropics. There are no final answers in this complex field.
Insects and other pests can often be removed from the small garden by a variety of techniques. Removal of individual insects by hand is seldom feasible except in the case of spot infections of a few, such as large caterpillars. Large insects can be removed when seen during harvest, but few will be caught in most cases, and control is laborious and imperfect.
Simple sprays of water may be useful in dislodging insects from the plants. A strong spray will wash away aphids and small worms. Once on the ground, insects might have a difficult time finding their way to the plant once more, or may become victims of exposition to water or to predators. Thus, the garden hose can be a useful insect control tool.
Sometimes insect pests can be removed by shaking the plants. If a bucket of water containing detergent is placed under the plant, it is sometimes possible to shake insects into it, and most will then drown.
An unusual way of removing insects is to plant a species around the garden in which the insects are highly interested. The "catch" plants often attract an undesirable pest, which can then be eliminated with another technique. This technique must be used with caution to avoid multiplication of the insect on the "catch" plant itself, followed by its spreading to other plants.
Pests can often be removed by trapping. Perhaps the use of a "catch" plant can be thought of as a trap, but usually the word is restricted to use of an apparatus to catch the insect alive or lure him to his death. The best traps are the simple ones that cost little or nothing, that require very little effort, but that are highly effective.
A simple trap for slugs and snails, for example, can be nothing more than a few planks left on the soil surface. Slugs and snails hide under these and can easily be collected by lifting the boards, scraping the pests off, and feeding them to the chickens. Squash bugs will also hide under such boards, and can be smashed each morning.
Kerosene is an old favorite to kill insects that are lured to a light. However, water with detergent is almost as good. A light, preferably blue, is suspended over a container, and insects attracted to it fall into the liquid below. Cans or jars with funnel-like entrances, easy to enter, but difficult to leave, may be baited with a number of different compounds. Rotted fruits capture flies; stale beer attracts cockroaches; linseed oil attracts melon flies; sugary water attracts some fruit flies.
More sophisticated traps include electric grids that attract and electrocute insects, and suction-type traps using electric fans. Traps are now used in which the sexual attractant of the male or female is used to lure insects to poisoned bate or to their death. Such sophistication is generally not necessary for the small planting.
Insects and other pests are often destroyed by dusts and sprays, The techniques and substances vary with the pest. Some are very effective, others are of questionable value, and still others lose their effectiveness as the pests acquire resistance to them. In the small planting good sprays are those that are inexpensive, efficient, and that do not leave poisonous residues.
Some of the nontoxic materials effective against many insects are the following: Flour dusted on the surface of wet leaves by shaking a cloth bag of flour over them which becomes a sticky mess for many kinds of caterpillars. As the flour dries the insects are impeded and even killed. Fine clay sifted and suspended in water sprayed to the underside of leaves also traps or hinders insects. Kieselguhr or diatomaceous earth is even better. Skim milk powder, mixed into water and applied as a spray is also very effective.
Emulsions made from plant materials are very effective. The technique is to grind the foliage of a strongly smelling plant with water in a blender, to filter, and to spray with this. Some of the materials that are effective are hot pepper, onions and garlic, aromatic herbs and foul-smelling plants in general, marigolds, and tobacco. Dead and rotting insects made into spray are sometimes effective repellents. In any particular area a search for insect-free weeds will reveal plants to be tested as homemade sprays. The reasons they work may not be known, but effectiveness cannot be doubted.
There are a few commercial insecticides prepared from plants themselves. Most contain the natural insecticides, rotenone or pyrethium. These come in several commercial formulations under different trade names. These are very low in mammalian toxicity and can be used cautiously.
A few general-purpose insecticides are frequently recommended for small scale planting. Malathion is used for aphids, bean fly, caterpillars; leafhoppers and mealy bugs. Diazinon is used for aphids, bean fly, leaf hoppers, rose beetles, and white fly. Sulfur dust is used for mites of all kinds, including red spiders.
It must be remembered that all insecticides have potential short and long-term effects on the health of humans. They must be used according to law, and following manufacturer's instructions.
The extreme sensitivity to insect damage shown by the supermarkets is not the appropriate attitude towards homegrown fruits and vegetables. Strong measures taken to eliminate pests may leave hazardous residues. It is probably safer to tolerate a certain amount of damage, at least in the small planting. Careful washing and cutting away of damaged parts is desirable before use. Leaves with holes may not be attractive, but are just as edible as entire leaves.
Experience and experimentation
The ideas presented here for pest control are very old ones, in some cases used for generations before chemical controls were developed. Nevertheless, useful techniques for insect control in the tropics have never been organized into a compact body of information. Not all of the experience of the tropics can be mentioned here, for much is folklore., hearsay, or not even published. Therefore, experimentation in the small planting is appropriate. Observations should be recorded, perhaps in a notebook, and these can serve as guides for future treatments. Scientific experimentation is desirable, but may be a long way off. Therefore, farmers are advised to become "experts" through their own efforts and observations.
Diseases are usually not as important in the small planting as are weeds and insects. However, at times diseases can rapidly eliminate entire plantings or can make the food that is produced unattractive or inedible. It is impossible to eliminate all plant diseases, even when careful protection is given, such as sterilization of soil or production within a sealed greenhouse; plants can become diseased. The controls for serious diseases are extremely varied. In addition, they are often highly specific. Once a disease occurs it may be impossible to control it except for very specific methods that the small farmer may not know. It is our purpose here to provide a battery of general suggestions which will help disease problems in .many situations.
Pre-planting prevention and post-planting care
As in the case of insect control, disease control begins before planting. Removal of infected residues of previous crops and of weeds and trash from surrounding areas sometimes reduces subsequent disease problems. Since residues of previous crops and weeds may have beneficial effects as a mulch or even in repelling or destroying insects, it is not always obvious which technique
is the most advantageous. Nevertheless, when the previous crop was highly diseased, its residues should not be preserved, but should be destroyed by burning, by plowing under or by high-temperature composting.
Soils may become infested with serious specific diseases that attack the roots or the lower parts of the plant, and these disease organisms frequently survive for many years in the soil, even when susceptible crops are not present.
When root and stem disease are found in the same area for two consecutive years, there is good reason to suspect a permanent fungus or bacterium. A solution in some crops is planting a variety resistant to the disease. Purchased seed packets often describe the diseases to which a given variety is resistant. The farmer can not expect much success from experimenting with plantings of unknown resistance in the hope of finding an appropriate variety. Usually the resistant varieties are more rare than the susceptible.
Another possible solution is to plant the susceptible variety in another area or in several areas until a disease free area is located, it must be remembered, however, that a disease free area can easily be contaminated by transfer of infected plant materials, soil, farming implements, and even by walking from an infested to a disease free area. Or, the disease organisms can be reduced in a given area, but seldom eliminated, by expensive soil fumigation or by growing other crops resistant to the disease. Relatively long rotations in which the susceptible crop is grown in an infested soil only one year out of 46 years are not uncommon where soil-borne diseases limit production.
On the small scale of the greenhouse, it is possible to eliminate soil-borne diseases by sterilization with chemicals, heat or steam of all soil and of implements or containers that have come in contact with infested soil.
Elimination of diseased plants in a field infested with a soil-borne disease is seldom effective in reducing the spread of the disease in the field. However, this technique is useful in the case of some other diseases spread by insects, wind, or rain. It can be effective in the reduction of symptoms of insect-spread viruses. On removing diseased plants from a field they should be burned or buried to prevent contamination of other plants. Hands should be washed and the clothing changed before reentering a planting where diseased plants have been removed. A special case of preventative pre and post-planting care is the avoidance of tobacco smokers in the care of solanacaous vegetables, especially tomatoes and peppers. Such crops, unless they are resistant varieties, are inevitably infected by tobacco mosaic virus from the hands of smokers.
Use of disease-resistant varieties
The use of such varieties has been mentioned in the previous section. The small farmer can save himself many problems, by finding out about the disease that his crops are likely to experience, and by obtaining seed of resistant varieties when available. During some seasons, when a particular disease is not present, such seed may not yield any better than that of susceptible varieties. On the other hand, when severe attacks of disease do occur, planting disease resistant varieties will often make the difference between a successful crop and a crop failure.
Protection of one species by another
The possible influence of one species on the infection by disease of another has seldom been documented. Nevertheless, there is reason to believe that it does occur. One species may create a mechanical barrier to the spread of disease to another, or may confuse disease-bearing insects. Diversity among crops planted is advisable in the small planting. On the other hand, planting several closely related crops as tomato, pepper, and eggplant, or squashes, pumpkins, and cucumbers is likely to increase the spread of disease from one crop to another.
Small quantities of diseased tissue on an edible plant organ may have little effect on the edibility of the remaining portion. Therefore, some disease can often be tolerated or eliminated by cutting away diseased tissue. If harvested plant parts are not eaten promptly the disease can spread and destroy other parts of the edible organ.
Post harvest care
When the crop is harvested, the farmer may believe that the job is done. Not so. Bruised or cut organs are likely to deteriorate or rot more rapidly than uninjured tissues, They should be separated and marketed or eaten first. Damaged tissues can be healed by several days of moist heat in the case of sweet potato roots, but the same treatment increases deteriorization of tubers of the true yam. Isolation of diseased organs from the non-diseased is useful to reduce spread of rot. In the case of seeds, careful drying is very desirable, and if the moisture content of the air is too high, as in the humid tropics, it might be necessary to dry grains in artificial dryers. Once dried, seeds should then be stored in sealed containers. Seeds damaged by fungi may contain aflotoxins, poisons that reduce the value of seed for food or feed.
The small farmer is not likely to find controls for serious diseases by his own experience or experimentation. When all remedies tried fail, it is then time to grow a different crop.
Cite this article as:
Martin, F.W. 1985. Control of Weeds, Insects and Diseases. ECHO Technical Note no. 11.