Himalayan Balsam

The primary biological control method being studied and released to control Himalayan balsam (Impatiens glandulifera) is a highly specific rust fungus known as Puccinia komarovii var. glanduliferae. 

Researchers, specifically from the Centre for Agriculture and Bioscience International (CABI), have been developing this rust fungus as a sustainable, long-term, and environmentally friendly alternative to manual pulling or chemical spraying. 

Key details regarding this biocontrol method:

• How it Works: The rust fungus is native to the Himalayas (the plant's home range). It infects the leaves and stems of the plant, stunting its growth, reducing its vigor, and limiting its ability to produce seeds.

• Specificity: Extensive testing has shown that the rust is highly specialized and does not negatively impact native UK plant species.

• Approval and Trials: The rust fungus was approved for field release in the UK by DEFRA in 2014, making it the first fungal biocontrol agent to be released against a weed in the European Union.

• Strains Used: Since not all Himalayan balsam populations are equally susceptible, researchers have released different strains of the rust, including strains from India and Pakistan, to maximize effectiveness.

• Progress: The rust has successfully established itself in several UK sites, surviving the winter and re-infecting plants the following spring, according to trials conducted by CABI and partners such as the Yorkshire Wildlife Trust. 

This rust is considered a "bio-superhero" that could, in the long term, reduce the need for manual "balsam bashing". 

The biological control method currently being studied and implemented to control Himalayan balsam (

Impatiens glandulifera) is the application of a host-specific rust fungus known as Puccinia komarovii var. glanduliferae. 

Key Details of the Method

• Targeted Action: The fungus is a "natural enemy" from the plant's native Himalayan range. It is host-specific, meaning it only infects Himalayan balsam and does not harm native UK plant species.

• Mechanism: The rust infects the stems and leaves of the plant throughout the growing season. It draws nutrients away from the plant, which:

  • Stunts overall growth.

  • Increases seedling mortality.

  • Reduces the plant's ability to produce seeds.

• Deployment: First approved by DEFRA for release in 2014, the rust has since been introduced at numerous trial sites across the UK, including Scotland (since 2020) and most recently in Yorkshire (2024-2025). 

Recent Research & 2026 Updates

• Multiple Strains: Scientists discovered that not all Himalayan balsam populations are susceptible to the same fungal strain. As of 2026, researchers are continuing to identify and release additional strains (including ones from India and Pakistan) to match the genetic diversity of the weed in the UK.

• Synergistic Studies: Active research in 2026 involves examining how soil-dwelling beneficial fungi (mycorrhizas) and internal leaf fungi (endophytes) affect the rust's ability to infect the plant.

• Long-term Monitoring: A three-year study led by the University of Stirling (published January 2026) highlights the urgency of these biological controls by quantifying how Himalayan balsam die-back significantly weakens riverbanks during winter.