Cultural weed management system includes all aspects of good crop husbandry used to minimize weed interference with crop. These consist of the following: Hand weeding, Mechanical weeding, Tillage, Mulching, Burning, Flooding, and Crop rotation.
Cultural Weed Management Systems
1. Hand weeding
Hand weeding is one of the oldest methods of weed control and consists of hand pulling, hand slashing and hoeing and mowing of weeds. Most of the drudgery associated with subsistence farming in the tropics centres around the peasant farmer and his manual weeding effort.
Problems associated with hand weeding include the following;
A lot of drudgery and time consuming.
Limited agricultural productivity because there is a limit to the amount of land area that can be weeded manually.
Organizational and other logistics and supervisory problems associated with human labour make its use cumbersome.
2. Hand pulling
Hand pulling is a major weed control method used in crop production in many parts of the tropics. It is particularly used in controlling weeds in cereal crops such as rice that are traditionally broadcast seeded.
Advantages of hand pulling
It requires no additional tool.
It is best for controlling weeds in broadcast-seeded crop where chemical weeding is not practiced.
It is useful in removing weeds that have escaped other weed control measures.
It is laborious and full of drudgery.
It is expensive when cheap labour is in short supply.
Not suitable for controlling perennial weeds.
Weeds cannot always be completely pulled out of the soil.
3. Hand hoeing
This is by far the most widely used method of weed control in the tropics. It is a faster method of weed control than hand pulling and can be used in range of cropping systems.
This method of weed control is used after the weeds have emerged but before they get too tall to interfere with hoeing operations. Hoe weeding is applicable to both annual and perennial weeds. Weeding hoes can be broadly grouped into light and heavy hoes.
Generally, the short handled hoes are used in the humid part of the tropics while the long-handled heavy hoes are used mainly in the tropical savanna for seed bed preparations.
Advantages of hand hoeing
Both annuals and perennial weeds are controlled.
It is an effective weed control measure for crops in rows.
It provides a clean seed bed and loosens the soil.
It is suitable for small farm size.
Weeds are usually well established in crops before farmers start weeding.
Is labour intensive and could be expensive where cheap labour is in short supply.
It is unsuitable for larger farms.
Predisposes the soil to erosion as a result of clean weeding and loosening up of the soil.
The propagule of perennial weeds may be buried at depth beyond the reach of hand hoes, thus making the control of such weeds difficult.
Hand hoeing has a high risk of crop damage in many root and tuber crops.
This is another manual method of weed control used mainly in right of way, non-crop areas, bush clearing and in plantation crops. Hand-slashing is used in food crops for control of over grown annual weeds. The most widely used tool for manual slashing is the cutlass or machete and a sickle.
Advantages of slashing
It minimizes erosion.
It is more labour efficient than hand hoeing.
Disadvantages of slashing
Rapid regeneration of weeds is a major setback of slashing.
Crop reduction as a result of accidental damage during slashing.
High labour requirement.
Is not suitable method of weed control in field crops that are under water stress because the basal portions of the weeds continue to deprive the crop of the limited water?
5. Mechanical weeding
In mechanical weeding, a farmer channels energy produced by machines or animals into weeding operations. He gets more work done with the use of this type of energy than in hand weeding, when he not only produces the energy but also directs its use.
The plough and harrows are most often used to control weeds before the crop is planted and between the rows of growing crop. During ploughing, weed seeds that have remained buried in the soil are brought to the surface.
They then begin to germinate and if shallow tillage is done shortly afterwards the weed seedlings are destroyed. This is a particularly good method for controlling annual weeds.
For perennials, repeated tillage at relatively short intervals may be necessary. Each tillage operation destroys the top growth, and forces the weed plant to produce new growth at the expense of underground reserves. Eventually these reserves are exhausted and the plant dies.
Tillage should be aim at destroying the weed plant before they reach the stage of setting seeds. For this reason, even fallow or uncropped fields should be subjected to occasional tillage as a method of controlling weeds.
The point here is that if the weeds are permitted to produce seeds on fallow fields such seeds can easily be dispersed to the cropped fields.
Those that are not dispersed may remain viable for several years and pose a problem when that particular field is eventually cropped.
Advantages of mechanical weeding
Increase economic returns, consequently improving the farmers’ welfare.
Increases timeliness and precision in operations.
More areas of land could be cultivated.
Managing animals or machines is less problematic than managing human labour.
Disadvantages of mechanical weeding
The initial cost of machines is high beyond the reach of most farmers around the world.
It requires highly trained experts to maintain the machines.
Availability and cost of fuel may affect the cost of running the machines.
6. Animal drawn weeders
The use of animal-drawn weeders in the tropics is limited due to presence of tsetse fly which transmits the parasite trypanosome spp. to cattle in many humid and sub humid tropics. They are widely used throughout the arid and semi-arid savanna tropics.
Advantages of using animal drawn weeders
Low capital investment on source of power.
Low cost of maintenance as draft animals are fed on forages available to other animals.
Droppings from the animal serve as rich source of soil organic matter.
No specialized training is required to operate the tool and guide the animal.
Weeding implements is within the technological competence of most tropical farmers.
Animal-drawn cultivators and weeders fit into the cropping patterns and farming systems of most farmers in many grassland region of the tropics.
These implements can be used in both small and large farms.
Disadvantages of animal-drawn weeders
Productivity of the system and work output of the animals depends on the state of their health and expertise of the handler.
Precise cultivation and planting cannot always be obtained because of difficulty in controlling the animals.
The presence of tsetse fly and animal diseases makes it impossible to use animals in some parts of the tropics.
Religious beliefs and local customs of some parts of the tropics may make farming with animal difficult to practice.
7. Machine-powered weeders
Machine-powered weeding refers to all weeding operations where the power used for removing weeds is derived from machines which in turn are using fossil fuel as source of energy.
Advantages of machine-powered weeders
Weeding can be done more timely, reliably and cheaply than in manual or animal-drawn implements.
Weeding can be done in less time and large farm land can be weeded.
The same engine power can be used for other farm related activities such as tillage, planting, harvesting and transportation of farm produce.
The use of machines eliminates drudgery and reduces risk of labour uncertainties.
Disadvantages of machine-powered weeders
It is unsuitable where crops are not grown in rows.
Heavy capital investment is required to buy and maintain the machines and equipment.
Service maintenance and availability of spare parts are chronic problems facing machine-powered agricultural operations throughout the tropics.
Cropland has for centuries been cultivated primarily to provide a good seed bed for seed germination and seedling growth.
Other reasons for tillage include weed control. In addition to routine tillage, farmers usually carry out two distinct types of tillage for weed control purposes.
Types of tillage for weed control
These are delayed tillage and blind tillage:
Delayed tillage involves preparing the seed bed and waiting until the weeds emerge before lightly cultivating the soil again and planting the seeds.
The purpose of delayed tillage is therefore to destroy the first flush of weeds so that the subsequently planted crop can grow at a reduced weed pressure.
Blind tillage is when crop seeds are planted after the usual land preparation and lightly cultivated after weeds have emerged but before crop emergence. This type of tillage works well if weeds germinate ahead of the crop.
Pre-planting land cultivation
This has the objectives of burying weed seeds and incorporation of organic matter in to the soil and cut off weeds as close to soil surface as possible.
Use of tillage as a weed control method involving animal-drawn implements is often handicapped by the inability of animal-drawn cultivators to accomplish deep tillage satisfactorily even on light soil.
Mounds are more desirable in controlling weeds because in giant mounds the weed seeds are buried deep in the mounds, thereby reducing weed pressure.
Fire is used as a weed control device in practically all parts of the world, it is used mostly to remove plant growth and plant material prior to cropping and also destroy weed seeds lying close to the surface. Most of burning is done before crops are planted.
There are three types of pre-plant field burning that are carried out in agricultural land worldwide: the uncontrolled, controlled burning, and the direct burner-assisted burning.
9a. Uncontrolled burning refers to both the accidental forest (bush) fires and the type of burning deliberately started in the dry season of the savanna for hunting purposes.
Uncontrolled burning damages the landscape, destroys wild life, destroys homes and property, destroys vegetation, exposes soil to erosion and may destroy economic trees.
9b. Controlled burning refers to agricultural fires set by farmers for the purpose of creating a favorable environment for crop production and getting rid of unwanted vegetation.
Controlled burning is used extensively in forestry to reduce the accumulation of litter and reduce the risk of wild fires that could destroy forests and property. This type of burning is done when environmental conditions are favourable and winds optimum.
Hard-to kill weeds such as Imperata cylindrical, Andropogon spp. and Hyparrhenia spp. are often burned by peasant farmers during the dry season to stimulate new growth, which can then be fed to livestock before the cropping season begins or hoe weeded after the crop is established.
Advantages of controlled burning
It is a cheap way of getting rid of excess vegetation.
It adds nutrients such as P and K to the soil.
It reduces soil acidity.
It destroys animal pests and pathogens that use the fallow vegetation as alternative hosts.
Destroys weed seeds and soil borne pathogens.
It stimulates re-growth in perennial grasses and may be used to rejuvenate grass pastures.
It is a cheap and effective way to kill woody perennials.
Disadvantage of controlled burning
It results in rapid loss of soil organic matter.
Loss of non-metal elements, e.g. sulphur and nitrogen as gases.
Soil temperature, generated during burning is often not high enough and of long enough duration to ensure complete destruction of partially buried weed seeds and nematodes.
9c. Direct burning: This is a type of controlled burning where special burners (mobile field incinerators, propane flamers) equipped with propane gas are used for burning plant residues.
Advantages of Direct Burning
A good chance for complete and environmentally friendlier burning because there is practically no smoke.
The speed of the operation can be controlled.
Disadvantages of direct burning
It is expensive to buy special burners.
Is slower than controlled burning.
Reduces farmer net profit due to additional cost on fuel and machinery.
This is also an effective method of weed control, although its use is mostly limited to paddy rice and taro. Flooding kills the weeds by depriving them of oxygen.
Since many weeds can survive flooding if they are not completely submerged, it is important the water level is maintained high enough so that no parts of the weeds are exposed.
Generally, several weeks of water logging are necessary to destroy the unwanted vegetation.
Advantages of flooding
Helps to kill some soil-borne fungi and nematodes.
Anaerobic condition in flooded fields suffocates roots of dry-land plants and kills weed seeds.
Disadvantages of flood in gas method of weed control
It is not effective on well-established aquatic weeds that cannot be submerged.
It requires a terrain that is level or can be leveled.
Could only be used in areas where water is available and can be impounded.
Mulch is a layer of non-living material placed over the surface of the soil to smother the weeds and cut them off from direct sunlight.
Mulching, in addition to this favorable effect on soil organic matter, is useful in managing the fragile tropical soil and:
Mulching can help to conserve soil moisture;
Protect the soil from erosion;
Reduce soil surface temperature;
Increase water infiltration;
Maintain soil structure;
Provide favorable environment for biological activities in the soil.
Limitation of mulching
It is a labor-intensive activity particularly if the mulch has to be transported.
Most crops do not generate enough crop residues to provide effective ground cover.
To be effective, the mulching materials must cover the soil surface and smother weeds.
Covering the soil completely by the mulching material may interfere with other farming operations.
Mulching materials placed before seedling emergence may interfere with seed germination or the growth of seedlings.
Mulching material may serve as a trap for animal pest of crop, including promoting termite activity.
12. Crop rotation
Crop rotation is a valuable tool in weed control because many weeds are associated with certain crops:
Rotation play a long term role in weed control by preventing particular weed species from adapting to the growth cycle of specific crops
Rotating cereals with legumes and other trap crops is recommended for reducing Strigainfestations in small holder farms
Crop rotation also helps the farmer to rotate his herbicides, thus ensuring that weeds resistant to a particular herbicide do not take over in a field.