Weeds - its causes and management through biological means

Weeds affect human affairs in most of the areas of the earth. The major characteristics of weeds are their unwanted occurrence, undesirable features and ability to adapt to a disturbed environment. Weeds compete with crop species, lower yields, increase labour requirements and ultimately, increase food costs for the consumer. Biological control as a general term refers to the introduction of organisms into an ecosystem with the intention of controlling one or more undesirable species. Biological control includes the classical (inoculative), bioherbicides (inundative) approaches and herbivore management. Insects, mites, nematodes, plant pathogens, animals, fish, birds and their toxic products are major weed control biotic agents. Biological agents, mainly insects provide excellent biological control of prickly pear (Opuntia elatior and O. vulgaris by D. ceylonicus and D. opuntiae), water fern (Salvinia molesta by weevil, Cyrtobagous salviniae), water hyacinth (Eichhornia crassipes by weevils Neochetina bruchi and N. eichhorniae and galumnid mite Orthogalumna terebrantis) and Parthenium hysterophorus by chrysomelid beetle Zygogramma bicolorata. Some introduced bioagents were not a big success but provided partial control like in case of Lantana by agromyzid seedfly, Ophiomyia Lantanae, tingid lace bug, Teleonemia scrupulosa, Diastema tigris, Uroplata girardi, Octotoma scabripennis and Epinotia lantanae. Nevertheless, India has now caught up with the rest of the pioneers in the field by recently introducing a host-specific plant pathogen, Puccinia spegazzinii against mikania weed (Mikania micrantha) and thereby became the eighth country in the world to practise CBC (Classical Biological Control) of weeds with plant pathogens. As this technology moves forward, their use will become even more probable for growers searching to diversify their weed management system. It will usually require a long period of research and a high initial investment of capital and human resources.