Mode of weed seed dispersal

1) Wind

The agent of air disperses majority of weed seeds. Such weed seeds possess special organs to keep them float in air e.g. pappus (a parachut like modification of calyx into hairs or cotton like structure), comose (seeds are covered with hairs) and wings. Which help them to cross long distance with wind and germinate in a new habitat. Example: Ageratum conyzoides (gandhe jhar), Eclipta prostrata etc.

2) Water

Aquatic weeds largely dispersed through water. The seeds have special structure and lower weight per unit of seed with which they can float in water and carried away by the current of water. By runoff these seeds are deposited in the crop lands. Irrigation and drainage also act as the carrier of weed seeds. Example: Pistia, Monochori etc.

3) Animals

Many weed fruits and seeds are eaten by animals and birds. Depending upon the digestive mechanism and nature of the weed seeds 0.2-9.6% of the ingested weed seeds are passed in viable form with the animal excreta, which is dropped wherever the animal moves. This mechanism of weed seeds dispersal is called endozoochory. Several birds pickup weed fruits and seeds on their wings, feet and beaks and drop these during their flight. Dissemination of Lantana seeds for e.g. is chiefly through the birds like Indian Maina and Chinese Dove. Xanthium, Tribulus etc. are dispersed by animal through their hoof, skin and hairs.

4) Man

Careless operations of man (transplanting, harvesting, threshing, transportation of crop seeds), are largely responsible for the dispersal of weed seeds from the infected areas to the new habitat. Weed also dispersed through FYM or compost also because during decomposition of FYM or compost many weed seeds do not loose their viability, even if proper temperature and acidity are maintained. Example: Echinochloa colonum (sama) may get transplanted with rice and Vicia spp with seeds of wheat. Similarly farm implements are the possible agent since many weed seeds are get attached with the tools when used in the infested areas and are dispersed in the new areas cultivated by the tools as such.