Proliferation of thorny weed in State a cause of concern

Aana Thottavadi (Mimoa diplotricha), an invasive weed, has infested the landscape of Kerala acusing considerable economic and biodiversity loss. The plant "scrambles vigorously over other plants, forming dense tangled thickets. It smothers and kills indigenous flora. The sharp and re-curved thorns of the weed deter animals form grazing on it, according to scientific publications.The weed has infested all districts of the State and reached the fringe areas of forest lands. It can grow on waste lands, pastures, disturbed forests, plantations, agricultural systems and along roadsides and railway tracks and even in high altitudes, said K.V.Sankaran, coordinator of the Asia-pacific Forest Invasive Species network (APFISN).The thorn-less variety of the plant was introduced as nitrogen-fixing cover crop. However, the seed of the thorny variety got mixed with others resulting in its accidental introduction, said Dr.Sankaran who is also the director of the Kerala Forest Research Institute (KFRI), Peechi.The variety poses threat to forest ecosystems, agricultural land and pastures. It causes heavy damage to sugarcane, coconut, rubber tea, pineapple and upland rice. There have been instances in Kerala where the plant had spiralled up the coconut trees.The thick growth mimosa prevents the regeneration, reproduction and growth of indigenous species in infested areas. A toxin produced by the plant can cause vascular endothelial damage, necroses of the heart and liver and anaemia in cattle, Dr.Sankaran said.Agricultural land infested with Mimosa is difficult to harvest. Increased cultivation cost, reduced yield, loss of crops and soil degradation are the main economic impacts of mimosa. KFRI is planning to study the extent of spread of the weed and its impacts, including economic and biodiversity losses. 'Communist Pacha', 'Congress  grass', 'Lantana' and 'Mikanium' are the other invasive weeds reported from Kerala. However, the loss caused by these weeds are yet to be assessed, he said.The seeds of mimosa, which can remain dormant up to half a century, get dispersed through water and are carried in animal fur, clothing, vehicles, agricultural implements and machinery, according to the latest bulletin of APFISN.Uprooting and burning, grubbing and slashing are the most common methods for control. Biological control measures have also been tried in some countries, according to experts.

The Hindu, 16th March 2009