Implementing a Novel Weed Management Approach for Himalayan Balsam: Progress on Biological Control in the UK
Himalayan balsam (Impatiens glandulifera) is an annual plant native to the foothills of the Himalayas in India and Pakistan. Since its introduction to the UK as an ornamental plant in 1839, it has gradually spread throughout the country, and parts of Europe. In its invasive range, it inhabits riverine habitats, damp woodlands and waste lands, growing in dense monocultures, outcompeting native plant species and altering the invertebrate community. As Europe’s tallest annual plant species, each plant can produce up to 2500 seeds that can be ejected up to 7m away from the parent plant. As the plant dies back in the autumn, there is an increased risk of erosion and dead plant material entering the water course can lead to flooding. Control methods are limited due to its close proximity to water; chemical control is difficult and plants can be inaccessible. Manual removal is common but relies on volunteers; it is time-consuming and control work is required on a catchment scale to prevent recolonisation from upstream. Therefore, since 2006 a consortium of sponsors has funded research into the biological control of this weed. This method considers the introduction of damaging insects, mites or fungal pathogens that have co-evolved with their host plant in their native range. The natural enemies that are selected for risk assessment and potential release have a very limited number of plant species on which they can survive, often only on a single genus or species. Surveys to look for suitable natural enemies were undertaken from 2006-2010 in the foothills of the Himalayas in Western India and Pakistan throughout the growing season of the plant; and a range of insects and fungal pathogens were found to cause significant damage to I. glandulifera. However, the insects were found to have too broad a host-range; being able to feed and complete their life cycle on a number of Impatiens species. A rust fungus Puccinia komarovii var. glanduliferae was observed to infect Himalayan balsam throughout the areas surveyed, causing significant damage to infected plants both at the seedling stage (stem infection, usually leading to plant death) and leaves of maturing plants and, hence, was prioritised for further study. This article discusses the research conducted to date on an isolate of the rust fungus collected in the Kullu Valley, Himachal Pradesh, India (IMI 398718), as a biological control agent for Himalayan balsam, and summarises the results of the first releases of the rust in the UK from 2014-2016 (https://himalayanbalsam.cabi.org).
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Document Type: Research Article
Publication date: October 1, 2016
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