Landcare Research - Manaaki Whenua

Landcare-Research -Manaaki Whenua

Releases Set to Begin in the Cooks Islands

Delivering mikania rust to the Cook Islands.

Delivering mikania rust to the Cook Islands.

In 2014 New Zealand’s Ministry of Foreign Affairs and Trade (MFAT) agreed to fund a 5-year project to develop weed biocontol for the Cook Islands. The first agent to be developed under this programme has now been approved for release and successfully delivered to the Cook Islands, where it will be mass-produced and released.

The rust fungus Puccinia spegazzinii originates from South America and has recently been established against mile-a-minute (Mikania micrantha) in other Pacific Islands: Papua New Guinea (PNG), Fiji, and Vanuatu. Mile-a-minute, as its name suggests, is a rapidly growing vine, and has become a major weed throughout Asia and the South Pacific. In tropical conditions mile-a-minute is said to grow as fast as 80 to 90 mm in 24 hours. A weed of agricultural, environmental and urban areas, mile-a-minute will grow pretty much anywhere except in heavy shade. It produces thousands of lightweight barbed seeds that are easily spread by wind, people and animals, and plants can reshoot from broken stems. Crops can be quickly smothered and killed, threatening livelihoods of subsistence farmers.

The rust was discovered and developed by CABI Europe-UK and was initially released in India, China and Taiwan in the mid 2000s, although it only established in the latter where a new, more aggressive strain of the rust was released. The rust is highly host-specific and has a life cycle of 15-21 days. Tiny white spots appear on the leaf surface about 6 days after inoculation and these infections continue to grown and develop pustules, turning yellow by 11 days. The rust pustules erupt on the lower leaf surface, petioles and stems, maturing orange-brown in colour around 4-6 days later. These infections lead to cankering on the stems and death of leaves, weakening the vine.

With the help of plant pathologist Sarah Dodd, currently based in Port Vila, we were able to import rust-infected plants from Vanuatu into our containment facility and use these to infect mile-a-minute plants imported from the Cook Islands. Sarah reports that 2 years after the rust was released in Vanuatu the vine has been noticeably reduced there. Monitoring of the impact of the rust in PNG undertaken by Michael Day (Biosecurity Queensland) and Anna Kawi (National Agricultural Research Institute, PNG) also showed a reduction in plant density there following rust establishment.

After permission to release the rust in the Cook Islands was received, Quentin Paynter, who leads the project, and plant pathologist Chantal Probst flew to Rarotonga with some infected plants. Following clearance at the airport there was a short ceremony to formally hand the plants over to the Cook Island’s Ministry of Agriculture. The infected plants were then placed in a shadehouse amongst uninfected plants that, once infected, will be planted out in areas where mile-a-minute infestations are particularly bad. Experience elsewhere has shown this to be an effective method provided there is adequate water and humidity. The establishment success and impact of the rust in the Cook Islands will be monitored.

Meanwhile approval has also just been granted to release a rust fungus against cockleburr (aka Noogoora burr; Xanthium strumarium sp. agg) in the Cook Islands. “We imported Puccinia xanthii from Australia,where it has been successfully used against Noogoora burr, in our pathogen facility at Tamaki and undertook some work to confirm that it is safe to release in the Cook Islands and that populations there are susceptible. We plan to deliver the Noogoora burr rust to the Cook Islands in early June,” confirmed Quentin.

Also a molecular study of peltate morning glory (Merremia peltata) is underway to try and determine how and when this plant colonised the Pacific region. There are conflicting views about whether this invasive vine is native or introduced to various islands, which needs to be resolved before any further steps could be taken to develop biocontrol for this target. Thanks to those from around the Pacific who have provided samples already from Palau, Micronesia and the Solomon Islands. However, we would welcome many more samples from the region – please get in touch if you are able to help.

Many thanks to MFAT for providing the funds for this project through its International Development Fund. ACIAR providing the funding that allowed the rust to be released in Fiji and Papua New Guinea. Australian Government funding allowed the release of the rust in Vanuatu.