July 2003. An article from the New Scientists was put out on PestNet about a CABI biological control programme for Mikania micrantha Mile-a-minute. And this caused heated discussion with members expressing differing views. (see also Mikania – CABI research).
Here is the original articles under the title: Fungus in your tea, sir?
Tea estates in India, from Assam to Darjeeling, are said to be under attack from Mikania micrantha, a native weed of South and Central America. Farmers lose 30 per cent of their profits controlling it, either by slashing with machetes or with chemicals, but neither method is totally effective or practical. The weed is also a problem in south India, in teak and eucalyptus plantations.
There are now plans by CABI to attack the weed using the rust fungus, Puccinia spegazzinii. Tests have been done in England over a number of years, and now the fungus is in quarantine in India where further tests will be made. There are hopes that, if successful, the fungus will be used in China, Indonesia and Malaysia.
One member thought it was ridiculous! Mile a minute is the easiest weed to control, paraquat at low concentration is effective. Hand weeding is commonly practiced in small plots, but, in large scale blocks, chemicals, mostly paraquat and Sting, are commonly used by farmers. It was thought that only if the weed becomes resistant to herbicides should biocontrol be considered.
By contrast, Palau is working to eradicate Mikania micrantha from Palau. It was first seen there 10 years ago, and is now found in about 30 small infestations. Attempts began last year using a combination of cutting and herbicide. Frequent mowing will kill Mikania, but this is not always practical. I wonder if tea farmers could mow between the rows of tea plants every week or two. If the Mikania has not seeded, this will get rid of it in a few months. Garlon 4 (triclopyr) is the herbicide of choice. It is translocated, so it can kill the entire plant with basal application or by spraying only a few leaves. Sting is glyphosate, which is also translocated. These should be more effective than paraquat. Triclopyr is registered by the USEPA for forest work, but maybe not for farms.
The herbicide is applied by the “drizzle” method, developed in Hawai’i. It applies a thin stream of large droplets which effectively hit the target plant without affecting others. We have It should not be applied when it is hot, however, becauses it volatilizes and may damage nearby broadleaf plants even when there is no drift. Triclopyr does not kill grasses, which helps in Mikania control. One other good thing about glyphosate and triclopyr is that they have relatively low toxicity to humans, while paraquat is highly toxic and very dangerous to the applicator and anyone nearby.
Support was also received for the biocontrol programme from SPC, Secretariat of the Pacific Community, Mile-a-minute (Mikania micrantha) is the number one most important weed in many Pacific Islands countries and is still extending its range on many islands. It is of South American origin and is very invasive. It affects subsistence and commercial agricultural areas, fallow areas, and many disturbed natural habitats.
On a small scale (such as the confines of a farm or plantation) Mile-a-minute can be controlled fairly effectively using herbicides. However, in most cases this is not the case. Herbicides use and high levels of labour input will continue year after year on a given plantation/farm, and this would become uneconomical. This is because reinvasion of plantations by Mile-a-minute weed will occur from natural areas.
Biological control is the most promising option for controlling Mile-a-minute, both in agricultural and natural areas. CABI Bioscience have been conducting research on biological control of Mile-a-minute, so let’s wait for them to explain the safety of Puccinii spegazzinii.
A good biological control agent will not kill off its host plant (the weed in this case) but reduce the weed infestation to economically and ecologically acceptable levels. There should be still enough Mile-a-minute weed around for those wishing to utilise it for medicinal purposes. The negative impacts of Mile-a-minute certainly far outweigh the benefits such as herbal medicines. Maybe if everyone in India started harvesting Mile-a-minute it may be possible to suppress the weed, but this is unlikely to happen and is not possible for many other areas. If the fungi proves effective in controlling Mile-a-minute in India, it is likely that other countries will want to introduce it as well.
At low levels of weed infestation brought about by a good biological control agent and a combination of human labour and a herbicide, there should be low or no fungi in you cup of tea!