Rust fungus to tackle ‘out of control’ UK invasive

A specialist natural enemy of Himalayan balsam is being introduced as part of a trial to kill off the invasive plant that has spread throughout south Wales.

Invasive species cost the UK economy £1.8bn every year, according to government figures. Experts believe the UK is home to around 2,000 non-native species, with about 10-15% of these deemed invasive – a plant or animal that does not have a natural predator to keep its numbers in check.

Himalayan balsam, Impatiens glandulifera, first introduced in the UK in 1829, is one such plant that has invaded swathes of the River Wye catchment without much resistance, smothering native plants and reducing biodiversity.

But the Wye and Usk Foundation, alongside biocontrol specialists the Centre for Agriculture and Bioscience International (CABI), is hoping that a rust fungus, Puccinia komarovii var. Glanduliferae, from India, will be able to deal with the prolific plant, which is capable of firing hundreds of seeds up to 7m away thanks to their exploding seed pods.

This week, the foundation issued a tender to record the effects of the fungus three times across two sites in the catchment, over the growing season next year. It is hoped that the DEFRA-funded pilot will yield positive results as the current practice of pulling, cutting and spraying the plant has largely been ineffective, the foundation said. 

The final results of the pilot will be reported in December 2020. 

The introduction of the fungus was first trialled by CABI in 2014 on 75 plant species, which proved the rust was a true specialist on its host, meaning it poses no threat to other species.

The releases have continued across 15 counties in England and south Wales – 25 in 2015, 10 in 2016, 22 in 2017 and 10 in 2018.

To view the Wye and Usk Foundation tender in full click here