Author
Kathryn M. Pollard
k.pollard@cabi.org
CABI
Ascot
Coauthors
Natasha L Lawson-Hale, CABI, Ascot, United Kingdom
Sonal Varia, CABI, Ascot, United Kingdom
Marion K Seier, CABI, Ascot, United Kingdom
Abstract
In 2014 the rust Puccinia komarovii var. glanduliferae released against invasive Himalayan balsam (Impatiens glandulifera, Balsaminaceae) in the UK became the first fungal agent for classical weed biocontrol in Europe. To date, two rust strains have been released and over the past decade, the release strategy has been optimised to enhance infection in the field. Given the presence of different weed genotypes in the UK with some showing resistance against one or both rust strains, pre-release testing was conducted to ensure strain pathogenicity and virulence match towards individual weed populations and new strains from the native range are under evaluation. Despite these efforts establishment of the rust has been slower than anticipated. Released at over 120 sites, the fungus has successfully overwintered and persisted at only a limited number. High rainfall and flooding during the winter months have been identified as significant environmental factors impacting spore survival thus potentially affecting the rust’s ability to establish in certain regions in the UK. However, at sites where the rust has successfully persisted, infection has spread up to 2km from the original release point and there is anecdotal evidence suggesting a decline in local Himalayan balsam populations. Nevertheless, robust monitoring to quantify the full impact of the pathogen long-term has been inherently difficult, largely due to the highly variable nature of field populations of this annual weed.
keywords
invasive species
Impatiens glandulifera
post-release monitoring
fungal biocontrol agent
classical biological control
Highlights
The rust can overwinter and spread naturally at sites in the UK with anecdotal evidence of impact
Performance of the rust is variable and site specific
Monitoring the effectiveness of a highly variable annual plant has proven challenging