Controlling the mile-a-minute weed

Overview

Results

The team

Related information

So what's the problem?

Mikania micrantha (mile-a-minute weed or South American Climber) is a major invasive alien weed in many of the tropical moist forest regions of Asia, and is still invading new areas, such as Northern Australia. This neotropical vine is able to smother plants in agricultural and agroforesty ecosystems, and native habitats. Crops particularly affected include banana (Figure 1), coconut, coffee, cocoa, cassava, oil palm, pineapple, ginger, and teak. In Assam, the main impact is on tea production (Figure 2.) and herbicide residues in tea have resulted in some exports being rejected by the European Community (EU). In native ecosystems, the weed significantly reduces biodiversity, by swamping vegetation and out-competing native plants. Also, in the moist deciduous forests of India, the infestation by M. micrantha makes harvesting by tribal people of reeds, bamboo and other forest products difficult.

Conventional control methods of manual removal (slashing) or herbicide application, are expensive, ineffective, not sustainable, and can be environmentally damaging. Biological control offers a safe, environmentally benign and effective method for the control of invasive alien weeds; and has a proven track record. M. micrantha is an ideal candidate for biological control using introduced natural enemies, since it is rarely a weed in its native range in the Americas, where natural enemies are seen to exert a significant pressure on the occurrence and abundance of the species.

What is this project doing?

A project was commissioned by NR International under the Department for International Development (DFID)-funded Crop Protection Programme (CPP). The aim of the project was to investigate the environmental and socio-economic impact of the M. micrantha invasion in the Western Ghats (in Kerala and Karnataka states), in India, to map the distribution of the weed and develop a sustainable control strategy, based on biological control. The first phase of this project established base-line data in India, on the extent of the invasion with technical advice and information from CABI through consultancy. Socio-economic impact in home garden (small scale) production systems was also evaluated. Permanent sampling plots were established by Kerala Forest Research Institute (KFRI) throughout Kerala to monitor changes in the abundance of M. micrantha. Control options were also investigated, including the potential of native pathogens, as mycoherbicides by KFRI, and classical biological control, using exotic fungal pathogens from the native range of the weed in the neotropics, were assessed by CABI.

No suitable pathogens were found in India, but a coevolved neotropical rust pathogen, Puccinia spegazzinii, was selected as the natural enemy most suitable as a classical biological control agent for the weed. It is a very damaging pathogen; infecting all aerial parts of the plant (leaf, petiole and stem), leading to cankering and whole plant death. Isolates collected from Argentina, Brazil, Costa Rica, Ecuador, Peru and Trinidad and Tobago were evaluated in the CABI Europe - UK's quarantine facilities. The pathogen was found to demonstrate intraspecies specificity; each pathotype only infecting a selected number of genotypes of its host. The best pathotype(s) for introduction into each region in the invasive range of the weed thus need to be selected. The isolate from Trinidad was selected for the India populations of the weed and during comprehensive screening, and evaluation, was found only to attack a limited number of species within the genus Mikania and had a broad environmental tolerance. Following the submission of a dossier on the rust to the Indian Ministry of Agriculture (MoA), permission was granted to import the rust into quarantine at the National Bureaux of Plant Genetic Resources (NBPGR), New Delhi, in September 2002.

The second phase of the project was to implement the biological control strategy in Kerala (by KFRI) and Assam (by Assam Agricultural University [AAU]), after final screening and assessment of the rust under Indian quarantine, lead by the Project Directorate of Biological Control (PDBC). Permission to release the rust in the field was granted by the MoA in June 2005, and the release procedure was subsequently executed in 2006. The final part of the implementation phase was a training and information campaign, involving workshops to inform extension workers, tea growers and the forestry department about biological control and how to encourage the rust to establish in their weed infestations; and a media campaign to raise awareness in the general public to about the rust. The role of CABI in the phase of the project was very much one of facilitator, information provider and support.

Following the implementation of this project in India, funding was approved by the Department for International Development (Defra), Darwin Initiative (DI) to implement a similar project in China. This project focused on training of Chinese nationals in the techniques involved in the use of plant pathogens as classical biological control agents. An isolate of P. spegazzinii was imported into China from CABI for final assessment before full field release on mainland China.

Similarly, CABI was commissioned to supply an isolate of the rust to Fiji and Papua New Guinea (PNG) under a Department of Primary Industries and Fisheries (DPIF) project, funded by Australian Centre for International Agricualtural Research (ACIAR); and to Taiwan by the National Taiwan University (NTU), funded by the Forestry Bureau (FB). The rust was subsequently released in Taiwan and PNG.

Results so far

Puccinia spegazzinii, a potential classical biological control agent for Mikania micrantha (mikania) was released in Papua New Guinea (PNG) in early 2009. The fungus was identified and screened by staff at CABI's European centre in the UK, who discovered that although it was very damaging to species of mikania, it was unable to attack any plants outside this genus. The release project was led by the National Agricultural Research Institute, Kerevat, East New Britain and funded by the Australian Centre for International Agricultural Research (ACIAR), through Biosecurity Queensland’s Department of Employment, Economic Development and Innovation (DEEDI). The rust has spread rapidly within the huge populations of mikania on the islands, and surveys undertaken in October 2010 found the rust infecting plants up to 37 km from the initial release sites. It is particularly exciting to hear that the rust is not only spreading efficiently, but is also significantly reducing the growth and density of the weed in the field.

Project Manager