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Biocontrol introduction

Target pest: Hawkweeds (Pilosella, Hieracium spp.) (Asterales: Asteraceae)

Agent introduced: Puccinia hieracii var. piloselloidarum (Uredinales: Pucciniaceae), hieracium rust


Pre-1995 (accidental introduction), post-1995 (deliberate introductions)

Import source:

Ireland (post-1995)

Import notes:

Syrett et al. (2001) - a strain of the rust fungus Puccinia hieracii var. piloselloidarum was accidentally introduced and has established in New Zealand on Pilosella officinarum (syn Hieracium pilosella). Not all P. officinarum plants in New Zealand appear to be susceptible to this strain of the rust so two further strains have been imported for widespread release.

Smith (2011) - studies showed that mouse-ear hawkweed (Pilosella officinarum) populations vary in their susceptibility to P. hieracii var. piloselloidarum, and many are resistant to the strain accidentally introduced into New Zealand. Another two strains of the rust have since been imported from Ireland to improve the level of attack.

Release details:

Smith (2011) - first noticed in 1995 on plants collected from Molesworth Station [Marlborough District, South Island]. It is not known how it originally arrived in New Zealand. Subsequently two further strains from Ireland were deliberately released.


Landcare Research (2000b) - common.

Syrett et al. (2001) - Puccinia hieracii var. piloselloidarum is widely established on Pilosella officinarum [mouse-ear hawkweed].

Smith (2011) - occurs throughout the hawkweed-infested parts of the country.

Impacts on target:

Landcare Research (2000b) - may damage mouse-ear hawkweed [Pilosella officinarum] but plants vary in susceptibility.

Landcare Research (2001c) - Puccinia hieracii var. piloselloidarum is now widely established and, given the right conditions, can stunt the growth of susceptible Pilosella officinarum (mouse-ear hawkweed) plants.

Landcare Research (2013g) - causes slight damage to some mouse-ear hawkweed [Pilosella officinarum]; plants vary in susceptibility.

Peterson (2021b) - a field study has suggested that P. hieracii var. piloselloidarum may suppress the growth of infested plants by around 10-20%.

Impacts on non-targets:

Smith (2011) - it is extremely unlikely that P. hieracia var. piloselloidarum will damage anything other than Pilosella officinarum (mouse-ear hawkweed). Even other closely related hawkweeds are unlikely to be attacked.

Waipara et al. (2009) - to assess non-target impacts of pathogenic weed biocontrol agents, including Puccinia hieracii var. piloselloidarum, introduced to New Zealand, nationwide surveys were conducted 2000-2009, focussing on plants closely related to the target weeds. No non-target damage was observed for P. hieracii var. piloselloidarum, despite positive infection being observed on many of the host (target) plants at the same sites.

General comments:

Target species note (17 February 2024) - in the 1990s and 2000s, six biocontrol agents were introduced to New Zealand to control hawkweeds, specifically four weedy species that at the time were considered to be in the genus Hieracium (with three of those in the subgenus Pilosella). Subsequently, Pilosella has been recognised as a distinct genus [see Taxonomic note (17 February 2024) entry below]; the four weed species are now classified as Pilosella officinarum (syn Hieracium pilosella) (mouse-ear hawkweed), P. caespitosa (syn H. caespitosum) (field hawkweed), P. praealta (syn H. praealtum) (king devil hawkweed) and H. lepidulum (tussock hawkweed). Of the biocontrol agents, the rust Puccinia hieracia var. piloselloidarum and the gall wasp Aulacidea subterminalis attack only P. officinarum, the plume moth Oxyptilus pilosellae attacks both P. officinarum and P. caespitosa, the gall fly Macrolabis pilosellae attacks all three Pilosella species, and the hover flies Cheilosia urbana and C. psilophthalma attack all four hawkweed species. (All preceding information from Hieracium Control Trust (2000).) Additionally, Syrett et al. (2001) identify a fifth adventive hawkweed, Pilosella aurantiaca (syn Hieracium aurantiacum) (orange hawkweed), as a problem weed in New Zealand, stating it has only recently been regarded as weedy in this country, although it has been here since 1911. Host range trials indicate it will be attacked at significant levels by A. subterminalis and the two Cheilosia species (Syrett et al. 2001).

Taxonomic note (17 February 2024) - at the time that P. hieracii var. piloselloidarum was introduced to New Zealand, the target weeds (hawkweeds) were all considered to be in the genus Hieracium. Bräutigam & Greuter (2007) note that Pilosella was considered by many authors to be a subgenus of Hieracium but that in recent decades generic recognition of Pilosella had gained increased support. Bräutigam & Greuter (2007) recognise Pilosella as a distinct genus from Hieracium and reclassify the Euro-Mediterranean flora accordingly. Under this classification there are introduced hawkweeds present in New Zealand in both genera (Hieracium and Pilosella) [see Target species note (17 February 2024) entry above].


Bräutigam S, Greuter W (2007). A new treatment of Pilosella for the Euro-Mediterranean flora. Willdenowia 37: 123-137 https://doi.org/10.3372/wi.37.37106

Hieracium Control Trust (2000). Application to EPA (NOR00001) to import for release the insects Macrolabis pilosellae (Binnie 1878), Cheilosia urbana Meigen and Cheilosia psilophthalma (Becker 1894) for the purpose of biological control of hawkweeds, Hieracium spp. Environmental Protection Authority website https://www.epa.govt.nz/assets/FileAPI/hsno-ar/NOR00001/6b046d0b38/Application-NOR00001.pdf

Landcare Research (2000b). Who's who in biological control of weeds? Patua Te Otaota - Weed Clippings. Biological Control of Weeds Annual Review 1999/2000. August 2000, 6: 10-11 https://www.landcareresearch.co.nz/assets/Publications/Weed-biocontrol/weedcp00.pdf

Landcare Research (2001c). Future eaters. Patua Te Otaota - Weed Clippings. Biological Control of Weeds Annual Review 2000/2001. August 2001, 7: 3 https://www.landcareresearch.co.nz/assets/Publications/Weed-biocontrol/weedcp01.pdf

Landcare Research (2013g). Who’s who in biological control of weeds. What’s New In Biological Control of Weeds? August 2013, 65: 10-11 https://www.landcareresearch.co.nz/assets/Publications/Weed-biocontrol/whatsnew65.pdf

Peterson P (2021b). Hieracium rust: Puccinia hieracii var. piloselloidarum. The Biological Control of Weeds Book - Te Whakapau Taru: A New Zealand Guide (Landcare Research) [Update of Smith (2011)] https://www.landcareresearch.co.nz/discover-our-research/biodiversity-biosecurity/weed-biocontrol/projects-agents/biocontrol-agents/hieracium-rust/

Smith L (2011). Hieracium rust: Puccinia hieracii var. piloselloidarum. The Biological Control of Weeds Book - Te Whakapau Taru: A New Zealand Guide (Landcare Research) [Updated 2021 - see Peterson (2021b)] https://www.landcareresearch.co.nz/discover-our-research/biodiversity-biosecurity/weed-biocontrol/projects-agents/biocontrol-agents/hieracium-rust/

Syrett P, Smith L, Grosskopf G, Meurk C (2001). Predicting the likely success of biological control of hawkweeds in New Zealand. Plant Protection Quarterly 16(4): 172-176 https://caws.org.nz/PPQ1617/PPQ%2016-4%20pp172-176%20Syrett.pdf

Waipara NW, Barton J, Smith LA, Harman HM, Winks CJ, Massey B, Wilkie JP, Gianotti AF, Cripps MG (2009). Safety in New Zealand weed biocontrol: a nationwide pathogen survey for impacts on non-target plants. New Zealand Plant Protection 62: 41-49