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Pests > Pest Management > Biological control > Bioagents – microbial > Rust, biocontrol, Mikania micrantha, Pacific
May 2015. An article was put out on the biocontrol of Mikania micrantha, and a discussion occurred on the relative control of Mikania species using the rust, Puccinia spegazzinii. The article is below and a poster on the rust published by SPC, Fiji is also provided.
P. spegazinii can infect Mikania cordata. M. cordata is native to Southeast Asia including Papua New Guinea (PNG) and probably occurs as far east as Solomon Islands. The decision to release P. spegazzinii in PNG was based on the understanding that the range of M. cordata is from sea level to above 2000 m above sea level, while that of M. micrantha and P. spegazinnii may be limited to about 1200 m. M. micrantha has not been found above 1000 m in PNG. Based on this and because M. micrantha is more aggressive and common than M. cordata, PNG concluded that controlling M. micrantha was of paramount importance in the lowlands.
As predicted before P. spegazzinii was released, non-target attack has been reported in the field where M. cordata and M. micrantha coexist in Papua New Guinea. However, there is anecdotal evidence to suggest that M. cordata populations are much less affected by the rust than M. micrantha and the attack is probably spill-over that only occurs in close proximity to infected M. micrantha (see Barton J (2012) BioControl 57:289–305. Predictability of pathogen host range in classical biological control of weeds: an update).
It seems likely that P. spegazzinii won’t have a major impact on M. cordata.
The rust was introduced in Solomon Islands some years ago, but no studies have been done on its efficacy. Mikania is still abundant!
A rapidly-growing vine that is smothering trees and plants all over Rarotonga could be under control in a few years, thanks a combined effort to fight its unrelenting spread.
Involving New Zealand’s Ministry of Foreign Affairs and Trade, Landcare Research New Zealand and the Cook Islands Ministry of Agriculture, the fight took an important step forward yesterday when the first seven samples of mile a minute vine infected with a rust fungus were formally handed over to the Ministry of Agriculture at Arorangi.
The fungus (puccinia spegazzinii), comes with an impressive track record, having already been introduced to curb mile a minute’s spread in countries including India, China, Fiji, Papua New Guinea and Vanuatu.
Auckland-based Landcare Research entomologist Quentin Paynter, who with plant pathologist Chantal Probst oversaw the importation of the fungus-infected plants, says the mile a minute project is part of a $1 million plan to introduce biological controls for a number of the most invasive weeds in the Cook Islands.
Following a short ceremony yesterday morning, Probst took a wheelbarrow full of freshly-gathered mile a minute plants and placed them under infected samples in the Ministry of Agriculture’s shadehouse. The infected plants will eventually release rust fungus on to the new plants. In this way stocks of control plants will be built up and they’ll then be planted in areas where mile a minute infestations are particularly bad.
Though the infected plants were looking a little the worse for wear after spending three days in a chilly bin while they went through the all-important clearance process, they are expected to revive quickly.
Paynter says while the fungus will bring the vine under control, it will never completely eliminate it, and those who use it in traditional medicines need not worry about mile a minute disappearing anytime soon.
There are also no concerns that the fungus, which comes from South America, will affect other plants, he says.
“It is highly specific and only attacks mile a minute.”
While it’s difficult to estimate how quickly the control will work on Rarotonga, Paynter says colleagues in Vanuatu saw a noticeable reduction in the pest vine after just two years.
In tropical conditions mile a minute or mikania micrantha, to give it its biological name, is said to grow as fast as 80 to 90mm in 24 hours.
In the future, biological controls will be introduced to the Cook Islands for a range of nuisance plants including the annual cropping weed cockleburr and the balloon vine, which is also spreading rapidly on Rarotonga.
Paynter says there is long history of successfully using biological control agents in the Cook Islands.