Manual cultivation

Hand pulling is the oldest and one of the most effective mechanical methods, as human energy is directly utilised. It is of minor value to the control of established perennials as underground parts are usually not disturbed. Hoeing is a widely used technique in the tropics. It is a highly effective method of weed control, however it is labour intensive.

Machine tillage (cultivation)

This can involve any implement powered by animals or machines and the method is often less effective than manual methods. It is generally effective against annuals and shallow rooted biennials but may not kill deep rooted biennials. It may be applied before (cultivation) or after (tillage) a crop emerges and the mode-of-action is to bury small weeds, pull up others by loosening the soil around the roots and kill the plant by desiccation. Tillage is used to prepare the land for furrow irrigation but tends to create favourable conditions for weed seed germination. Deep rooted perennials are controlled only by depletion of food reserves through continuous destruction of top growth.

Mowing and cutting

Sickles, scythe, axes, and mowers have only a limited value as a means of weed control. Their primary aim is to restrict unsightly weed growth. They are commonly used along road sides and in waste places. These methods may help control weeds when applied at or before the bud stage because they prevent seed production. They also deplete food reserves, especially in perennials. Generally, mowing is ineffective against prostrate or short weeds growing close to the ground.

Flooding, dredging, draining, and chaining

Flooding deprives weeds of air and the ability to carry out photosynthesis. It is only effective when the roots and shoots are covered and when the situation prevails for a sufficiently long period of time. Its success is confined to terrestrial plants. Dredging, draining, and chaining are techniques that can be used on aquatic weeds.

Heat

Fire is often used to burn accumulated debris that is a health hazard or is unsightly especially on railroads, canal banks, drainage ditches and road sides. Flaming kills young plants if their cambium reaches 50^oC. To use this technique the crop plant must be larger than the weeds, have woody stems, be resistant to intense heat and the flame should be directed towards the ground. The technique is used in cotton, sugarcane and soybean crops.

Smothering with non-living materials

Hay, manure, grass clippings, straw, sawdust, wood chips, rice hulls, paper, and plastic film can be used to completely exclude light from the growing weed. This prevents photosynthesis and further growth. Cost of materials and residues make this an expensive option.

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