Worldwide complexity of weeds

Abstract

No more than 3% of the total plant species on the Earth account for weeds, but they cause significant problems to humankind by intruding in food security and safety, health, environment, economic stability, and welfare. The problem of weeds as a worldwide problem increases, as human activities and their interference with the environment are increasing. Weeds owing to their forceful and flexible nature, cause considerable losses in agriculture, forestry, aquaculture, water supply and a variety of other human enterprises. Overall, weed-crop competition is the most important cause reducing sustainable crop production. They decrease production due to competition, allelopathy, and by providing environment for pathogens, serving as alternate hosts for numerous insects and fungi, thus causing an increase in harvesting expenditures. Weeds are prominent yield reducers, often economically more significant than insects, pathogens or other biotic constrains altogether. Worldwide damages generated by weeds are responsible for a loss of 13.2% of crop yields, but the probable losses in agricultural production without weed control are predicted at 20-90% globally.