Impatiens glandulifera, or Himalayan balsam, is a prolific invader of riverine habitats. Introduced from the Himalayas for ornamental purposes in 1839, this annual species has naturalised across Great Britain (GB) forming dense monocultures with negative affects across whole ecosystems. In 2006 a programme exploring biocontrol as an alternative control method was initiated and to date, two strains of the rust fungus Puccinia komarovii var. glanduliferae have been released. To better understand the observed differences in susceptibility of GB Himalayan balsam stands to the two rust strains, inoculation studies were conducted using urediniospores and basidiospores. Experiments revealed large variation in the susceptibility of stands to urediniospores of the two rust strains, with some resistant to both. Furthermore, the infectivity of basidiospores was found to differ, with some stands fully susceptible to the urediniospore stage, being immune to basidiospore infection. Therefore, before further rust releases at new sites, it is necessary to ensure complete compatibility of the invasive stands with both urediniospores and basidiospores. However, for successful control across GB it is essential that plant biotypes are matched to the most virulent rust strains. This will involve additional strains from the native range to tackle those biotypes resistant to the strains currently released.

Plant species have been introduced increasingly into non‐native ranges, where many have become exotic weeds with adverse impacts on native ecosystems, as well as on farming and other livelihoods. In biological control, the classical or inoculative approach is the one most commonly used for the management of invasive alien weeds and is based on the use of co‐evolved natural enemies from the native range to control the invasive weed. Typically, the inundative or mycoherbicide approach targets problematic weeds using local plant pathogens that, in the case of introduced species, have ‘jumped’ onto the exotic host. The leaf‐spot fungus, Mycosphaerella polygoni‐cuspidati, co‐evolved with its host, Reynoutria (Fallopia) japonica (Japanese knotweed), in Japan and has a unique history of being investigated both as a classical biological control agent and a mycoherbicide against this highly invasive weed in the United Kingdom and North America. Here, we highlight our research on M. polygoni‐cuspidati as part of a biological control programme for Japanese knotweed and review the potential of mycoherbicides using exotic pathogens for the management of invasive alien weeds. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

A little known, unculturable ascomycete, referred to asPhyllachora ambrosiae, can destroy the inflorescences ofAmbrosia artemisiifolia, an invasive agricultural weed and producer of highly allergenic pollen. The fungus often remains undetectable in ragweed populations. This work was conducted to understand its origin and pathogenesis, a prerequisite to consider its potential as a biocontrol agent. The methods used included light and transmission electron microscopy, nrDNA sequencing, phylogenetic analyses, artificial inoculations, and the examination of old herbarium and recent field specimens from Hungary, Korea, Ukraine and USA. The Eurasian and the North American specimens of this fungus were to represent two distinct, although closely related lineages that were only distantly related to other lineages within theAscomycota. Consequently, we describe a new genus that includesCryptophyllachora eurasiaticagen. et sp. nov. andC. ambrosiaecomb. nov., respectively. The pathogenesis ofC. eurasiaticawas shown inA. artemisiifolia. No evidence was found for either seed-borne transmission or systemic infection. Two hypotheses were developed to explain the interaction betweenC. eurasiaticaandA. artemisiifolia: (i) as yet undetected seed-borne transmissions and latent, systemic infections; or (ii) alternative hosts.

Cryptostegia grandiflora and C. madagascariensis (Apocynaceae) are the only two species of this Madagascan plant genus. Both have been transported around the world as ornamentals due to their attractive flowers and based on a perceived potential as sources of rubber – hence, the common name rubber vine – because of their copious latex, which also contains toxic cardiac glycosides. As a result of their vigorous growth and ability to climb over and smother vegetation, both species have become invasive, posing an actual or potential threat to native ecosystems in many tropical and sub-tropical countries, as well as to human and animal health. Classical biological control (CBC), or the introduction of co-evolved natural enemies to control an invasive alien species in its exotic range, has successfully been used to tackle C. grandiflora in northern Queensland, Australia. This strategy is currently being evaluated for its suitability to manage C. madagascariensis in north-eastern Brazil using the same Madagascan rust fungus, Maravalia cryptostegiae, released as a CBC agent in Australia. For CBC to be successful, it is critical to understand the taxonomy of the invader as well as the origin(s) of its weedy biotype(s) in order to select the best-matched co-evolved natural enemies. Based on an exhaustive search in published and unpublished sources, we summarise the taxonomy and uses of these rubber vines, follow their historical movements and track their earliest records and current weed status in more than 80 countries and territories around the world.