The Food & Environment Research Agency is consulting on taking a non-native rust pathogen out of scientific quarantine and using it as a natural way to kill Himalayan balsam in England.
Scientists from UN scientific charity CABI researching the natural enemies of Himalayan balsam imported Puccinia komarovii from India in 2010 under quarantine for evaluation. Now they believe it could work as a natural pathogen in the UK.
The Environment Agency estimates that it would cost some £300m to eradicate Himalayan Balsam using current methods.
CABI tests show the rust is autoecious (completes its life cycle on one host plant species), macrocyclic (has all five spore stages present in the life cycle) and causes "significant damage to Himalayan balsam (see box). Tests also show the rust would not affect other plants.
Landscape professionals have welcomed the move. David Layland of Japanese Knotweed Control said: "Overall biocontrol is a good concept if it's been done in a controlled manner. It only targets that species, they assure us. It needs something to control the spread but it's not an instant solution."
He said he did not think bringing in the pathogen would affect his or other specialist contractors' business much because most of the market remains in Japanese knotweed eradication.
BALI Technical director and Ground Control training director Neil Huck said: "I'm always in favour of biocontrol if it doesn't affect native and commercially important species. Himalayan balsam is a nightmare and the seeds are extremely persistent."
His only concern is if the rust behaves differently in the wild than in the laboratory and affects linked plants, such as impatiens, which is the same genus and sold in large numbers.
Amenity Forum chairman John Moverley said: "The scientific results look positive and show that only the target species will be affected by the controlled release. This is important in any decisions relating to introduction of natural controls as clearly a key factor is any potential unforeseen effects."
The consultation runs until 16 June. See http://www.fera.defra.gov.uk/plants/nonNativeControl/pucciniaPRA.cfm.[QQ ] How it works - Effect of rust on plant life
In early spring the aecial spore stage of the rust develops on the stems of seedlings, warping the stem as the plant grows and often resulting in collapse before the plant reaches maturity.
In June/July, the aeciospores infect the leaves of the plants in the wider population resulting in the development of urediniospores and, in August/September, teliospores on the leaves of the plants, reducing the area for photosynthesis.
When infection rates are high the urediniospore infection can lead to premature leaf fall, resulting in early plant death.