How Do Weeds Spread?

There are actually no such things as weeds. When a farmer plants certain seeds which he hopes will produce a valuable crop, he calls any other plant which grows up in his field and interferes with his crop a weed! Basically, though, weeds are plants that do harm. Some are poisonous to cattle and horses. Others injure crops by robbing them of sunlight, soil, minerals arid water. Others act as parasites, or serve as hosts to insects or plant diseases that cause harm. Weeds are spread by various means. Some are carried from place to place in fodder, in dust, in rubbish and in manure. But most weeds that cause so much trouble do not spread because of man's carelessness. They have their own devices for spreading their seeds.     

Some 'weeds, such as pimpernel, nightshade, dodder and grasses, produce their seeds in such great quantities that some of them are likely to survive practically no matter what the conditions.Other weeds have hairlike or wing like projections on their seeds and fruits. These make it possible for the seeds to be carried by the wind for considerable distances. Such weeds include dock, sorrel, thistle and dandelion. Still other weeds have little hooks or spines' on their seeds. These hooks catch in the fur of animals or in the clothing of man, and in this way the seeds are spread to new territory.

Some of the most successful weeds do not even spread by means of seeds. They have spreading underground stems which send up erect branches. If the underground stem is cut, these erect branches merely become separate plants.
Because of the harm they can do, weeds are fought and controlled by man. Today there is a whole variety of chemicals that have been developed to destroy weeds or prevent them from appearing.