Biocontrol introduction
Target pest: Ageratina riparia (Asterales: Asteraceae), mist flower
Agent introduced: Entyloma ageratinae (Tilletiales: Tilletiaceae), mist flower fungus
Imported:
1998
Import source:
Jamaica/Mexico via Hawai'i
Import notes:
Fröhlich et al. (2000) - following a study on the feasibility of transferring the successful biological control programme for A. riparia in Hawai’i to New Zealand, Landcare Research decided to proceed with plans to import two biological control agents, E. ageratinae and the gall fly Procecidochares alani, from Hawai’i. Permission to import and release E. ageratinae was granted by the Ministry of Agriculture, and the fungus was shipped from Hawai’i to New Zealand on 5 October 1998, on inoculated, detached A. riparia leaves.
Released:
1998
Release details:
Fröhlich et al. (1999) - Entyloma ageratinae was released at nine sites (three in Northland, four in Auckland, two in Waikato) in the northern half of the North Island between 19 November and 23 December 1998. Releases were made as either a suspension of conidia in water painted onto A. riparia plants or by transplanting into the field A. riparia plants that had been infected in the glasshouse.
Establishment:
Fröhlich et al. (1999) - at all nine release sites E. ageratinaea was found to have established and caused secondary infections on inoculated and neighbouring plants within 4-6 weeks. At eight sites spores were not yet evident on plants further than 200 mm away from the inoculated plants, but at one site were found on leaves 3-10 m from the inoculated plants.
Fröhlich et al. (2000) - four of the nine release sites were monitored again 3-7 months after release. Characteristic symptoms and spores of E. ageratinae could not be found at one site but were present at the other three. At two Auckland sites, E. ageratinae plants within a 5 m radius of inoculated plants were found to be suffering severe disease symptoms, with up to 50% necrotic tissue. Lesions and spores of E. ageratinae were found on A. riparia leaves up to 12 m from inoculated plants at one of these sites and up to 450 m from inoculated plants at the other.
Barton et al. (2007) - Entyloma ageratinae developed damaging infestations at all nine of the 1998 release sites. After establishing at all these sites, the fungus dispersed rapidly. For example, within 2 years it had crossed the Hauraki Gulf to reach Great Barrier Island, about 80 km from the nearest release site. By June 2004 (5.5 years after its release) all known North Island A. riparia sites had plants that were infected by the fungus, up to 440 km (in Wellington) from the nearest release. The only place in the South Island where A. riparia is known to occur is in Nelson; by June 2004, the fungus had not yet been found there.
Impacts on target:
Barton et al. (2007) - the impact of E. ageratinae was monitored annually from summer 1998-99 to summer 2003-04, at up to 51 sites in the North Island. The mean percentage of live leaves infected with fungus rapidly reached nearly 60%. Maximum plant height declined significantly. In heavy infestations, mean percentage cover of A. riparia declined from 81 to 1.5%, and across all infestations there was a drop in mean percentage cover of 85.9% from summer 1999-2000 to summer 2003-04. The dramatic reduction in the percentage cover of A. riparia at all study sites in the 4-5 years after the release of E. argeratinae, and the high levels of infection of leaves, are consistent with biocontrol being highly successful.
Landcare Research (2009a) - in November 2008 a survey was undertaken in the Waitakere Ranges, Auckland (at the same sites last surveyed in 2003) to assess the progress of the biocontrol agents released against A. riparia: E. argeratinae (released 1998) and the mist flower gall fly Procecidochares alani (released 2001). Both agents were found to be still abundant and A. riparia still under excellent control in the Ranges. Entyloma argeratinae was infecting, on average, 55.4% of living leaves, consistent with the 4-year-post-release result (around 58%). In study plots in the Waitakere Ranges in 1998 the average percentage cover of A. riparia was 5.45% (and the maximum 36%). In 2008 the average per plot was 0.16% (maximum 0.46%). The fungus still appears to be having a dramatic impact on overall plant health and biomass.
Hayes et al. (2013) - a preliminary analysis of financial savings from no longer having to control mist flower by conventional means in the upper North Island suggests a cost reduction of $80,000 to $90,000 per year from the introduction of E. ageratinae and the gall fly Procecidochares alani in 1998 and 2001 respectively. The net present value for this is more than $3 million with a benefit:cost ratio of 2.5:1; considered very good over a 13-year period.
Landcare Research (2017g) - Entyloma ageratinae often causes severe damage, providing excellent control.
Impacts on non-targets:
Fröhlich et al. (1999), Fröhlich et al. (2000) - host range tests had been conducted on 55 plant species prior to the release of E. ageratinae in Hawai’i and South Africa. Thirty-five additional plant species of significance in New Zealand were tested, in Hawai’i, prior to the release of the fungus in New Zealand. Representative plants for this additional testing were chosen from New Zealand native plants, especially in the Asteraceae (daisy) family, ornamental Asteraceae grown in New Zealand and plants known to host fungi that are closely related to E. ageratinae. All host range tests have shown E. ageratina is highly specific to A. riparia. The only symptoms of infection on a non-target plant were small lesions on Ageratina adenophora (Mexican devil weed, also an aggressive weed in New Zealand). However, E. argeratina could not complete its life cycle on Mexican devil weed in laboratory tests and has not been recorded from that plant in the field in Hawai’i or South Africa, even when growing beside infected mist flower. Thus, E. ageratinae is likely to be restricted to A. riparia in the field and poses no threat to non-target plants in New Zealand.
Barton et al. (2007) - a study in the Waitakere Ranges, Auckland from summer 1999-2000 to summer 2003-04 showed that as A. riparia declined due to the impact of E. argeratinae, the species richness and mean percentage cover of native plants increased. In contrast, the species richness and mean percentage cover of exotic plants (other than A. riparia) did not change significantly. Many plant species colonising the plots were important native mid- or late-successional shrubs or trees. With few exceptions, the exotic plant species common in the plots were not weeds that appeared to threaten native forest habitats. There was only a weak “replacement weed effect” from the potentially serious invader African club moss (Selaginella kraussiana). Overall, it seems certain that the suppression of mist flower attributed to successful biological control has benefited native plants in many parts of the Northland and Auckland regions of New Zealand.
Waipara et al. (2009) - to assess non-target impacts of pathogenic weed biocontrol agents, including Entyloma ageratinae, 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 E. ageratinae, despite positive infection being observed on many of the host (target) plants at the same sites.
References
Barton J, Fowler SV, Gianotti AF, Winks CJ, de Beurs M, Arnold GC, Forrester G (2007). Successful biological control of mistflower in New Zealand: agent establishment, impact, and benefit to the New Zealand flora. Biological control 40(3): 370-385 https://www.landcareresearch.co.nz/uploads/public/researchpubs/mistflower.pdf
Fowler S (2007). Mist Flower Fungus. In The Biological Control of Weeds Book (Landcare Research) https://www.landcareresearch.co.nz/discover-our-research/biosecurity/weed-management/using-biocontrol/the-biological-control-of-weeds-book/
Fröhlich J, Fowler SV, Gianotti AF, Hill RL, Killgore EM, Morin L, Sugiyama LS, Winks C (1999). Biological control of mist flower (Ageratina riparia, Asteraceae) in New Zealand. Proceedings of the New Zealand Plant Protection Conference 52: 6-11 https://journal.nzpps.org/index.php/pnzppc/article/view/11611/11461
Fröhlich J, Fowler SV, Gianotti AF, Hill RL, Killgore EM, Morin L, Sugiyama LS, Winks C (2000). Biological control of mist flower (Ageratina riparia, Asteraceae): transferring a successful program from Hawai’i to New Zealand. Proceedings of the X International Symposium on Biological Control of Weeds 2000, pp. 51-57 https://www.invasive.org/publications/xsymposium/proceed/01pg51.pdf
Hayes L, Fowler SV, Paynter Q, Groenteman R, Peterson P, Dodd S, Bellgard S (2013). Biocontrol of weeds: achievements to date and future outlook. In: Dymond JR (ed) Ecosystem services in New Zealand: conditions and trends. Manaaki Whenua Press, Lincoln, pp 375-385 https://www.landcareresearch.co.nz/__data/assets/pdf_file/0005/77054/2_8_Hayes.pdf
Landcare Research (2009a). Still working after all these years. What’s New in Biological Control of Weeds? February 2009, 47: 7-8 https://www.landcareresearch.co.nz/assets/Publications/Weed-biocontrol/wtsnew47.pdf
Landcare Research (2017g). Who's who in biological control of weeds? Weed Biocontrol: What's New? 81: 10-11 https://www.landcareresearch.co.nz/publications/newsletters/biological-control-of-weeds/issue-81
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
