AN EXOTIC fungus may help save your favourite cup of tea from a plague of green weed that is strangling India鈥檚 tea crops, from Assam to Darjeeling. Scientists are planning to introduce the rust fungus later this year to kill off the weed, although they must first check that the fungus itself won鈥檛 run amok and kill other plants.
Researchers have long been searching for a biological agent to kill the weed Mikania micrantha. 鈥淭he plant can grow at a phenomenal rate,鈥� says Sean Murphy at CABI Bioscience in Egham, UK. 鈥淚n the monsoon season it is like seeing a green tidal wave coming down from the hills.鈥�
The hardest hit tea-growing states are in the north-west of the country, and include Assam, Darjeeling, West Bengal and Megalia. Farmers lose 30 per cent of their profits controlling Mikania, dubbed the 鈥渕ile-a-minute鈥� weed, with chemicals and armies of machete-wielding workers. But this isn鈥檛 always successful, because chemicals can only be used early in the season, to avoid contaminating the crop鈥檚 leaves. In the worst cases, growers lose their entire crop, says Narender Kumar Jain, secretary of the International Society of Tea Science in New Delhi. 鈥淭hey just abandon them, they can鈥檛 pick them,鈥� he says.
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Mikania was introduced to India in the Second World War to camouflage airfields, but without any natural enemies it spread uncontrollably. In southern India, the weed is also a problem in teak and eucalyptus plantations.
Now, after a 7-year search for a suitable biocontrol agent, Murphy鈥檚 team have settled on the rust fungus Puccinia spegazzinii, which attacks the weed in its native South and Central America. The fungus has been delivered to India after testing in England to check that it doesn鈥檛 harm other Indian plants. It is now in quarantine, where it will undergo further tests before a planned release later in the year. If successful, Murphy hopes the fungus could also be deployed against Mikania in China, Indonesia and Malaysia.