(a) The methods of weed dispersal are:- (i) Dispersal by Animals: Weed seeds such as desmodium possess adhesive substances which make them stick to passing people or animals and hence are carried to some distance by the people or animals they stick to. Some also have hooks, while rodents and birds carry edible fruits of weeds from one place to another (ii) Dispersal by wind: Some weeds have fruits or seeds with structures which adapt them to wind dispersal. They are light, e.g. Tridax, Aspillia africana. (iii) Dispersal through Explosive Mechanisms: Some weeds possess pods which, when dry, explode and scatter. e.g. Calapogonium, centrasema, pureria etc. (iv) Dispersal by water: Weed seeds like coconut are carried to long distances in water. Seeds dispersed by this method have light, hollow fruits which enhances their buoyancy.
(b) The mechanical methods of controlling weeds are: (i) Hand pulling/hand picking:- This Involves uprooting weeds from the soil by hand. It is mostly used by peasant farmers and it is most effective for the control of annual and biennial weeds of raw crops. (ii) Hoeing: This involves uprooting weeds with hoes before or after planting. Roots of uprooted weeds are exposed to sunlight and killed. Hoes may be used to bury the weeds. (iii) Slashing: Through this method, the aerial part of the weeds are removed with cutlasses, leaving behind the roots in the soil. This can also be done using mowers mounted on tractor. (iv) Rotary cultivation: This involves using hand drawn implements to undertake the ploughing and burying of weeds.
(c) The cultural methods of weed control are: (i) Flooding:- Flooding is one of the best ways of cultural weed control. Under this method, the farmland is surrounded by dikes and water is led into it, up to a height of 15-30 cm for about 6 weeks. The method is effective for controlling weeds with underground perennial organs.
(ii) Burning: Burning as a cultural method of weed control involves setting the vegetation on fire, usually when preparing the land for planting. This method is effective for controlling weeds propagated by seeds and aerial portions.
(iii) Mulching:- Mulching involves the placement of dead inactive materials e.g. grass or straw around planted crops. It also prevents weeds from sprouting and smothers those that have sprung up.
(iv) Cover cropping:- This involves the planting of fast growing crops especially legumes such as mucuna and calopogonium on land to act as cover and to smother weeds. This method is effective in controlling weeds on plantation farms.
(v) Crop rotation:- Crop rotation is an effective way of Controlling weeds associated with specific crop. The crops grown on the land are rotated to exclude the preferred crops and the weed is starved to death.