Lantana leaf rust off to great start
Jenny Dymock with a defoliated plant at Whangaroa Harbour. Inset: infected leaf.
Although lantana (Lantana camara) has a reputation for being one of the world’s 10 worst weeds, in New Zealand it is mostly only problematic in Northland, with much of the country fortunately being too cold for it to thrive. However, given lantana’s potential, especially since our climate is warming, biological control has been attempted here as a ‘pre-emptive strike’ rather than the more usual tactic of ‘last resort’. The early signs are that this strategy is likely to be highly successful.
After receiving advice from Michael Day (Biosecurity Queensland), who has worked extensively on lantana biocontrol in Australia, that none of the insect agents were likely to thrive in New Zealand conditions, we focused instead on two rusts from South America. The lantana leaf rust (Prospodium tuberculatum) causes leaf-death and defoliation and the lantana blister rust (Puccinia lantanae) causes dead patches on stems, leaf stalks and leaves, and sometimes systemic infection leading to stem dieback. With the assistance of Michael’s team in Australia, and Carol Ellison, Sarah Thomas and colleagues at CABI in the UK, we were able to determine that New Zealand lantana is susceptible to both pathogens and that no other significant damage to beneficial plants was likely to occur. With Northland Regional Council as applicant, a successful case was then made to the Environmental Protection Authority in 2012 to release both rusts. The leaf rust is well established in Australia but the blister rust had never been used as a biocontrol agent anywhere before.
The rusts were imported once our new plant pathogen containment facility was up and running in Auckland in 2013. After some initial teething problems successful transfers of both species onto potted plants were achieved. This allowed mass-rearing to get underway and field releases in Northland and the Bay of Plenty regions to begin in autumn 2015. Both rusts require warmth and moisture for infection, so spring and autumn are the best times for releases. The climatic requirements of the two rusts differ slightly. The lantana leaf rust is subtropical whereas the lantana blister rust is tropical. The expectation, therefore, was that the lantana leaf rust would likely be active across a wider area in New Zealand, including the more southern parts of lantana’s range, while the lantana blister rust might be limited to the warmer and wetter areas of the Far North.
An unusual cold snap in winter 2015 caused frost damage to some lantana in Northland and concern about what that might mean for the recently released rusts. However, in August 2016 Jenny Dymock (who helps the Northland Regional Council with biocontrol activities) reported seeing lantana that “was not looking quite right”. So a group of Landcare Research staff checked out these sites with her in September. There was much excitement when it quickly became obvious that some lantana plants had been heavily defoliated at the Whangaroa and Cable Bay sites, with tell-tale signs of the leaf rust present on remaining leaves. “We did not expect to see this much damage so soon,” said Lynley Hayes. “We were amazed at how easily infected leaves would drop at the slightest touch.” Pathologists Chantal Probst and Mahajabeen Padamsee subsequently examined collected samples and confirmed that the leaf rust was the culprit. Since then Jenny has found similar damage and evidence of leaf rust establishment at Kohukohu in north Hokianga.
The blister rust had also been released at Cable Bay and Kohukohu but there are no signs yet that it has established. “The blister rust is a little more difficult to work with. Unlike the leaf rust, which can be applied to the leaves as spores mixed with talcum powder, whole plants infected with blister rust need to be placed in the field and survive long enough for disease transmission to occur,” explained Lynley. The two rusts have never been found co-occurring naturally although they happily do on plants in the lab so it is presumed this will be possible in New Zealand.
We will now be watching with interest the impact the leaf rust has on lantana plants over time, and how quickly it spreads, while keeping a hopeful eye out for the appearance of the blister rust.
This project was funded by the National Biocontrol Collective with additional funding provided by Northland Regional Council, Auckland Council, Bay of Plenty Regional Council, and Greater Wellington Regional Council.