Alternanthera philoxeroides (Alligator weed), a South American weed of the family Amaranthaceae, has been found in the lakes and water pools in the eastern parts of India, namely, West Bengal and Bihar. It is a noxious invasive weed. This species was introduced long ago in the tropics of the Old World, but its introduction into India has taken place during late years. This weed has recently also been found in Northern India.
As other American weeds, some fertile seeds of Alligator weed may have arrived in India with packing material during the Second World War. This weed species was first found in Kolkata. It reproduces vegetatively using Subterranean Shoots and under favorable temperature and moisture, it spreads rapidly and grows in masses.
Alligator weed was recorded during the vegetation survey of Wular Lake, Kashmir. Wular Lake, the largest freshwater lake in India, is located 34 km northwest of Srinagar at an altitude of 1580m. It is a shallow lake with a maximum depth of 5m and water temperature range from 2°C to 29.5°C during the year. It also provides important habitats to the migratory water birds. Because of the importance of the wetland to biodiversity, it was described as a Wetland of International Importance under Ramsar Convention.
The flowering of Alligator weed takes place in June-October in Kashmir. During the survey of the lake, the weed was found in six areas. The invasive shrub forms floating Islands on the lake. It forms dense and large masses, thus creates problems for the aquatic environment by obstructing light to enter and not allowing gaseous exchange. It also creates a probable ground for breeding of mosquitoes.
This noxious weed can be managed and controlled by chemical, mechanical and biological methods. The use of Flea Beetle in biological methods is quite effective in eradication of weeds. Mechanical or manual control involves local eradication of the weed at a few locations. Using 1% glyphosate for free floating alligator weed is effective. Inspection and proper survey should be done on a regular basis to check on the spread of the weed.
It is the time to develop and implement a management plan for alligator weed before it grows into uncontrollable rate and proportions.