Aquatic Weeds: Occurrence and Distribution
The unwanted plants that grow in the wetland are termed as aquatic weeds. They generally grow in the fields and compete with crops for water, soil nutrients, light and space, and crop yields are reduced. They also harbour insect pests and microorganisms. Weeds belong to the class Angiospermae (flowering plants) which have two subclasses: Monocotyledoneae (monocots) and Dicotyledoneae (dicots). On the basis of the habitats, they are divided into terrestrial and aquatic categories, and on the basis of the duration of life, they are divided into annuals, biennials and perennials. A number of chemicals are used for controlling some submerged aquatic weeds by dissolving or emulsifying them in water in canals, ditches, ponds and lakes. Some chemicals in use are aqualin, aromatic solvents, chlorinated benzenes, copper sulphate, endothall, Fenac, sodium arsenite and 2,4-D. Unwanted aquatic plants are the number one pond maintenance problem. With the arrival of warm temperatures, they annoy pond owners and create problems throughout the summer and fall. Depending on the species and abundance of these weeds, it is often necessary to control them. Aside from the aesthetic value of a well-kept pond, an over abundance of weeds can create a hazard for aquatic life, offensive odours, breeding grounds for mosquitoes and a hindrance to water sports. There are three basic ways of controlling aquatic weeds. Mechanical, biological and chemical aquatic weeds are those unabated plants which grow and complete their life cycle in water and cause harm to aquatic environment directly and to related eco-environment relatively. Water is one of most important natural resource and in fact basis of all life forms on this planet. Therefore, appropriate management of water from source to its utilisation is necessary to sustain the normal function of life. It is one important part of natural resource management. Quarantines are legislative tools that may be used to mitigate the effect of weeds. Quarantine is defined as the restriction imposed by duly constituted authorities, whereby the production, movement or existence of plants, plant products, animals, animal products, any other article or material or the normal activity of persons are brought under regulation in order that introduction or spread of a pest may be prevented or restricted. If a pest has already been introduced and established in a small area, a quarantine is necessary so that it may be controlled or eradicated or dissemination stopped in newer areas, thereby reducing the losses that would otherwise occur through damage done by pest.