Organic weed management

Y Sanatombi Devi / M Sumarjit Singh / Priyaka Irungbam / Y Bebila Chanu *

Weed are no strangers to man. They have been there ever since man started to cultivate crops about 10,000 BC and undoubtedly recognized as a problem, from the beginning. In India, the manual method of weed control is quite popular and effective. Of late, labour has become non-available and costly, due to intensification, diversification of agriculture and urbanization.

The use of herbicides in India and elsewhere in the world is increasing due to possible benefits to farmers. At the same time, the continuous use of the same group of herbicides over a period of time on a same piece of land leads to ecological imbalance in terms of weed shift, herbicides resistance in weeds and environmental pollutions.

Application of herbicides for controlling aquatic weeds in a pond also reduces dissolved oxygen and pH and increase biological oxygen demand. The complexity of these situations has resulted in a need to develop a holistic sustainable eco-friendly weed management programme throughout the farming period.

Sustainable development is the management and conservation of the natural resource base and the orientation of technological and institutional change in such a manner as to ensure the attainment and continued satisfaction of human needs for present and future generations. There are three different approaches are involved in sustainable weed management are as follows:

o Cultural method
o Mechanical method
o Biological method

Cultural methods:

Cultural practices of weed control exploit the crop’s competitive behaviour, growing environment and crop management practices towards smothering of wees. Cultural practices including crop rotation, intercropping, mulching, soil solarization, sowing crop (seed rate) etc. are important tools in farming system.

These practices can also have secondary benefits for soil fertility, disease and pest management. These practices if used properly help in controlling weeds. Cultural practices alone cannot control weeds, but help in reducing weed population.

Crop rotation: Crop rotations should be designed that make it difficult for weeds to grow and reproduce. It is way to avoid use of herbicides. Certain crops can suppress weeds by out-competing them for water and nutrients, or by shading them so they cannot receive adequate sunshine. Choice of crop rotation strongly affects the abundance and diversity of weed flora.

Rotation crop with different life cycles can disrupt the development of weed crop associations through different planting and harvest dates preventing weed establishment and therefore weed seed production. Weed densities were lower when a crop was grown in rotation.

Intercropping: In organic or other system where herbicides are not used, intercropping can reduce the yield loss potential and provide stability in the system. Intercropping system and enhance the utilization of resources such as light, heat and water. These practices can also help to suppress weeds and increase the likelihood of being able to reduce herbicide use in the cropping system.

Weed suppression, the reduction of weed growth by crop interference, has been referred as one determinant of yield advantage of intercropping, being a viable alternative to reduce the reliance of weed management on herbicide use.

Soil solarization: The basic principle behind soil solarization is that light received from the sun is in the form of electromagnetic short waves, which easily pass through the transparent colourless polythene films and reach the soils. As a result soil is heated upend emits long wave terrestrial radiation which, however can’t pass through transparent polythene film and result in build-up or trapping of heat.

Weed seeds and young seedlings are killed by the heat and moisture and through direct contact with the plastic, which causes scorching. Thinner transparent sheet (0.05 mm) were better in controlling weeds than thicker one (0.1 mm) due to low cost and has high strength.

Guidelines for using soil solarization:

o Soil must be finely tilled, and plastic trap must fit tightly over the soil.
o The recommended soil temperatures for solarization are 1400F at a depth 2 inches and 1020F at a depth of 18 inches.

Mulching: The mulch provides a physical barrier on the soil surface and must block nearly all light reaching the surfaces so that the weeds which emerge beneath the mulch do not have sufficient light to survive.

Mulching reduces the deterioration of soil by way of preventing the runoff and soil loss, minimizes the weed infestation and reduces water evaporation. Mulches of organic material, such as straw, stubble, crop residue left on the surface can also effectively block sunlight and are more commonly used in organic row crop production systems.

Certain cover crops also may be used as living mulches. Living mulches can be established before planting, or they can be seeded with or after the main crop has been planted. Living mulch suppress the weeds by shading and cooling the soil.

Stale seed Bed:

A stale seedbed is one where initial one or two flushes of wees are destroyed before planting of a crop. This is achieved by soaking a well-prepared field with either irrigation rain and allowing the weeds to germinate. At this stage a shallow tillage may be used to destroy the dense flush of young weed seedlings. This technique allows the crop to germinate in almost wee-free environment.

Crop Sowing

Seed rate : Lowest seed rate recorded significantly, higher weed density and dry matter accumulation than higher seed rate. Higher seed rate significantly influence weed population and their dry weight by securing an optimum plant population which shows excellent smothering effects on weeds and improving productivity and profitability of the crop.

Mechanical method

Hand weeding: It is done by physical removal or pulling out weeds by hand. It is probably the oldest method of controlling wees and it is still a practical and efficient method of eliminating weeds in cropped area.

It is very effective against annuals, biennials and controls only upper portions of perennials. This method is useful for small-scale infestation. It is best to hand pulling wees after rain, when soil is moist.

Hand hoeing: It is a post-planting intercultural operation which stirs the soil and makes it more loosened and digging up to deeper layers so as to remove underground storage organs. It is very helpful in the case of perennial weeds and it is done with the help of pick axes.

Tillage: The objectives of tillage to provide a good seed bed and a root bed for smooth germination and better root growth and subsequent rapid seedling establishment and to reduce/control initial flushes of weeds by means of exhausting weed seed bank remain unchanged.

Tillage brings about alternations in the physical chemical and biological properties of soil and thus, it favours crop growth and influences competition behaviour. Tillage breaks cuts or tears off weeds and exposes them to desiccation by sun. It reduces population of perennial weeds by exhausting food reserves of the vegetative structures.

Flooding: Flooding is successful against weed species sensitive to longer periods of submergence in water. Flooding kills weed by reducing oxygen availability for weed growth. The success of flooding depends upon complete sub- mergence of weeds for longer periods. Flooding constitutes an important mechanism/aspect of weed management in rice.

Mowing: Mowing may also play a critical role in managing weed in forage crops or non-crops area. Repeated mowing reduces weed competitive ability, depletes carbohydrates reserves in the roots, and prevents seed production. Mowing can killed or suppress perennials and biennial weeds. It can also suppress perennials and help restrict their spread thus, decreases the long term development of the weed population.

A single mowing will not satisfactory for weed control, however mowing 3 or 4 times per year over several years can greatly reduce the occasionally eliminate certain weeds. Regular mowing help prevent weeds from establishing, spreading and competing with desirable forage crop.

Biological method

It involved the use of bio agent that affect the health of the weed or reduce weed population. An important aspect of biological weed control is that at a time, it is applicable to the control of only one major weed species that has spread widely.

With perennial weeds the main objective of bio-control is the destruction of the existing vegetation, in the case of annual weeds prevention of their seed production is generally more important.

Allelopathy: Allelopathy is defined as any direct or indirect harm induced in one plant through toxic chemicals released into the environment. Such weed control will neither harm the environment nor increase and management costs. Allelopathy weed control may be applied as a single strategy in certain cropping systems, such as organic farming.

Small seeded and slow germinating crop are more likely to be adversely affected by allelopathic cover crops than large seeded rapidly germinating crop. Under allelopathic weed management, the allelopathic potential of crop is manipulated in such a way that the allelochemical from these crops reduce weed competition.

Allelochemicals can be found in different concentrations in several parts of plants (leaves, stems, roots, rhizomes, flower and even pollen). Such chemical are release from plant parts by leaching, volatilization, residue decomposition, root exudation.

Bioagent: Pests that attack part of weed can reduce the number of weed present, which in turn can reduce the size of future weed populations. This lowers the effort needed to control the remaining emerging weeds.

Bioherbicide: Herbicide listed by the Organic Materials Review Institute (OMRI) for use in organic production as of May 2004. All product listed are classified as listed

Corn gluten meal: Corn gluten meal is a by-product of corn processing. The use of corn gluten meal as herbicide was patented in 1991. It can be use as an organic herbicide. CGM displayed pre-emergence herbicide effects during a series of turfgrass and also affected the small seeded annual and perennial weed.

Corn gluten meal works by inhibiting the root formation of germinating plants. It should be applied before germination of weeds. If it does not rain in 5 days of application, water it in with approximately 0.25 inches of water. Then leave a drying period after germination.

Herbicidal soap: Made from ammoniated soap of fatty acid, it is a non-selective weed killer that can be used within vegetable and flower garden, landscape areas and may be used in cultivated area. It kills moss, algae and weed. Best results are obtained with young, actively growing weeds, less than 5 inches in size. Larger weed may require second application.

Vinegar: Vinegar has proven itself an effective weed killer. It is a non-selective bioherbicide. Unlike commercial weed killers, vinegar is eco-friendly and won’t harm people, pets or the environment.

Steps for preparation:

1. Pour 1 gallon of white vinegar into a bucket.
2. Add 1 cup of table salt. Stir the solution with a long-handled spoon until all the salt dissolves.
3. Stir in 1 tablespoon of liquid dishwashing soap. This will act as a surfactant and make the vinegar and salt solution adhere to the weeds more efficiently. Blend thoroughly.
4. Funnel the weed killer into a plastic spray bottle
5. Drench the weeds with the solution on a dry, sunny day.
6. Any plants soaked with this solution will die within several days. They won’t be back and nothing else with ever grow there.

Conclusion:

Increase in chemical residue in harvested produce of crop if such type of food eaten by human being it causes harmful effect due to disturbance of food chain. To eliminate the harmful effects of chemical methods of weed control there is one option that is eco-friendly weed management for sustaining ever growing population.

Maintaining appropriate crop rotation with legume and non-legume crops, and growing of cover crop helps to suppress weeds by smothering and allelopathic effects. Growing competitive cultivars, modifying in sowing and planting techniques and mulching with organic residues, and the adoption of tillage operation makes an inappropriate environment for weed seed germinations and their growth.