Invasive weed species – a threat to sustainable agriculture

There are two main threats to biodiversity in the world. One of them is the direct inadvertent destruction of habitats by people which is done basically through inappropriate resource use or pollution the other highly serious but under estimated problem is the threat to natural and semi-natural habitats by invasion of alien organisms it is the lasting threat as compared to the first one because when exploitation stops the existing aliens do not disappear but continue to spread and consolidate. Our planet is quickly being taken over by hundreds of hardy aggressive species spread either knowingly or accidentally by human hands these are considered the second most significant threat to biodiversity after habitat destruction. These weeds are causing damages worth billions of dollars world wide and Pakistan being no exception. The countries rich repository of 6,000 of vesicular plants is highly threatened by a number of alien weeds among those some are worth mentioning such as Parthenium weed (Parthenium hysterophorus), Lantana (Lantana camara), Paper mulberry (Brossonetia papyrifera), Mesquet (Prosopis juliflora), Wild tamarind (Leucaena leucocephala), Khakiweed (Alternanthera pungens) etc. These weeds especially P. hysterophorus are highly noxious plant species and threatening the natural and agriculture ecosystem of the country. Parthenium is allergenic to both humans and animals and after invading Punjab is quickly moving towards NWFP. This is primarily because of unawareness about this plant and secondly that it is being constantly used in floral bouquets. Similarly there are many more in the list developed by IUCN in the year 2000 for Pakistan. Though it is difficult to manage these aggressive alien organisms but success stories have been documented regarding biological/chemical control and other integrated approaches. More over a careful revision of legislation regarding quarantine and enforcement of the same may prove useful to mitigate the threats of these weeds