Release update

Public consultation

On the 6 May 2014 Defra requested views from the public regarding releasing the Himalayan balsam rust, Puccinia komarovii var. glanduliferae from its quarantine restrictions. The public consultation gathered stakeholder’s views and lasted for six weeks. In total, 19 consultation responses were received, 13 of which were supportive of the principle of releasing the rust, three did not support the proposal and three submitted views on the detail of the consultation but offered no view on the proposal. All questions and queries highlighted were addressed by CABI.

Technical Workshop

In addition to the public consultation, a technical workshop was held at the Wildfowl and Wetland Centre in Barnes, London on the 5 June 2014. This event informed interested stakeholders on the biological control of I. glandulifera that CABI have researched. Over 30 representatives from 24 organizations attended the meeting where CABI presented a holistic review of the research which included a full description of the ecology and biology of the rust along with an evaluation of the scientific methods we used in determining the host specificity of the rust.

Approval of the Pest Risk Assessment

Following a positive review by FERA in 2013, the Pest Risk Assessment (PRA) was presented to the European Commission’s Standing Committee on Plant Health in Brussels in June 2014. Following some clarification, the Committee agreed that the PRA was sufficient at an EU-wide level and supported the release of the Himalayan balsam rust in the UK.

On the 23 July 2014, the Himalayan balsam rust was approved for release by Defra Ministers making this the first fungal biological control agent to be released against a weed in the European Union.

The release

The first experimental releases of the biocontrol agent were made at three authorized locations in Berkshire and Cornwall in August 2014. These sites were carefully selected as they had discrete populations so we could carefully monitor the spread of the rust and stable populations where the leaf litter, containing the overwintering spore stage of the rust (teliospores), had a lower chance of being washed away by high river flows. Natural England granted a license under the Wildlife and Countryside Act 1981 allowing CABI to plant up to eight pre-infected Himalayan balsam plants at each site. These were infected with the cycling spore stage of the rust (urediniospores).

Himalayan balsam plants were pre-inoculated with the rust within laboratories at CABI’s UK science centre in Egham and once chlorotic spotting appeared on the underside of the leaves (indicating that the rust was close to maturity) the plants were placed out in each site. The pre-infected plants were observed fortnightly for signs of rust development, and the wider field population of plants was monitored for signs of spread of the rust. At both sites in Berkshire, secondary infection was observed on Himalayan balsam plants growing in close proximity to the initial release plants, proving that the rust is able to infect its host under natural conditions in the UK.

In the winter of 2014/ 15 experiments were set up to examine the infection of Himalayan balsam seedlings in the spring. Spermogonia and aecia developed on the stems of young seedlings following infection from the overwintering spore stage (teliospores, which release infective basidiospores) causing stems to become warped and elongated. This confirmed that the rust can successfully overwinter and complete its life cycle thereby sustaining its presence under natural conditions in the UK.

In the spring of 2015 a nationwide rust release and monitoring programme was initiated. The rust was released at 25 sites: Berkshire (2 sites), Middlesex (1 site), Kent (1 site), Gloucester (1 site), Cornwall (6 sites), West Yorkshire (4 sites), North Yorkshire (2 sites), Northumberland (4 sites), Swansea (2 sites) and Ceredigion (2 sites). Each site was visited throughout the growing season, at least four times; initially at release, followed by three subsequent monitoring visits.

The initial releases were made in the late spring (May/ June) and the rust was found spreading on to uninfected leaves of the inoculum plants and some field plants. Unfortunately, an unusually cold spring triggered the immediate development of the overwintering spore type (teliospores) on the field plants, rather than the cycling spore stage (urediniospores) as was expected.  Consequently, to supplement the low number of urediniospores present in the field, it was necessary to plant out additional rust infected plants during the second round of field visits 6-8 weeks after the initial release of the rust (July). A subsequent monitoring visit made six weeks after this second release, revealed urediniospore development on both inoculum source and field plants.

At this stage there is limited spread of the rust and pustule size was smaller in comparison to those observed on plants in the field in the Himalayan native range. However, the rust spread and pustules size is variable and better at some sites. To investigate the role of climatic and site specific variation (using the data-logger records) on infection, a recording protocol was developed to enable a comparison to be made between all of the UK sites.

Experiments were set up at field sites close to CABI in Egham to investigate the effects of a number of biotic and abiotic factors on the level of infection. These will continue throughout the autumn/ winter in growth rooms at CABI. Factors under investigation include: plant biotype variation in the UK, temperature and dew period impact, effect of different growing conditions on plant susceptibility and rust virulence and the role of plant endophytes. However, it is also important to give the rust time to adjust to the UK climate, which is inevitably different to that in the Himalayas. We may find that the rust ‘takes-off’ after a period of field hardening. Collecting new isolates of the rust from different areas of the Himalayas could be considered if necessary in the future.

Soil cores will be collected at a selected number of sites (once the plants have died back after the first frost) from outside of the area of rust infection this year. This will enable the collection of base-line data on seed density. This will be repeated each year within the rust release area to provide evidence of the impact of the rust over the subsequent years following release.

The CABI team have trained local collaborators in Cornwall, West and North Yorkshire and Northumberland to monitor and complete record sheets. The releases and monitoring of the rust will continue in 2016-17 in Wales, where the best infection was observed, and in Berkshire and Middlesex in order to study factors affecting infection.

We anticipate that a full country-wide release programme will resume in 2017, once the host-pathogen system in field conditions in the UK is better understood, and release strategies refined.

The majority of the funding for the 2015 releases was provided by Defra, Natural England and the Welsh Government. In addition, North West Kent and Medway Valley Countryside Partnerships have funded the Kent release, and a consortium of donors has contributed to the releases in West Yorkshire (Environment Agency, Yorkshire Water, Wakefield Council, Calder and Colne Rivers Trust).

We would like to thank all collaborators involved with the field releases this year for their support and careful monitoring of the rust in the field. We hope that this will continue in future years and lead to successful management of this noxious weed.