Lantana Rust Releases to Begin
Lantana (Lantana camara) is considered one of the world’s 10 worst weeds.
So far in New Zealand lantana is mostly only problematic in Northland, but it is an emerging weed, or at least one to keep an eye on given its reputation, in the Auckland, Waikato, Bay of Plenty and Wellington regions. Biological control is being attempted as a “pre-emptive strike” rather than the more usual tactic of “last resort”.
We received advice early on from Michael Day (Biosecurity Queensland), who has worked extensively on lantana biocontrol in Australia, that none of the many insect agents, which have been used with mixed success elsewhere, were likely to thrive in New Zealand conditions. One specialist lantana insect, a plume moth (Lantanophaga pusillidactyla) that feeds on the flowers, has self-introduced here but its impact is thought to be insignificant.
So we focused instead on two rusts from South America. The lantana leaf rust (Prospodium tuberculatum) can cause leaf-death and defoliation. The lantana blister rust (Puccinia lantanae) can cause 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 (both the pink and orange forms) 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 to release the rusts in 2012.
Once our new plant pathogen facility was up and running in Auckland in 2013 we imported both rusts with the aim of getting mass-rearing and releases under way. Unfortunately we ran into some unexpected problems. “The lantana leaf rust shipment was found to be contaminated with another fungus and by the time we had identified the contaminant and demonstrated that it would not be a risk, the spores were no longer viable,” explained plant pathologist Maj Padamsee. Another shipment was sourced and tested for viability on arrival, but we found that it was quickly rendered non-viable through storage at 4°C. However, with this knowledge it was third time lucky with another shipment received from Michael in spring 2014.
Things also did not go smoothly with the first shipment of the blister rust in 2013. Infected plants shipped from the UK got held up in transit and were slower than expected to develop symptoms. Spores were eventually produced and used to infect plants. However, after initial signs of successful inoculation the plants outgrew the symptoms and the rust colony was lost. While the plants were relishing the conditions in the facility, it was clearly too dry for the rust. Therefore humidity chambers were constructed to ensure the necessary 100% humidity could be achieved when needed. Then last spring Sarah Thomas kindly delivered a second shipment of the blister rust by hand and, with the benefit of her experience, successful infection was achieved.
Maj, and Chantal Probst, have managed to successfully bulk up both rusts over the summer and obtain permission to take them out of containment. Releases of both rusts are scheduled to get underway this autumn. Since both require warmth and moisture for infection, 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. Consequently, we expect the lantana leaf rust to be active across a wider area in New Zealand, including the more southern parts of lantana’s range, while the lantana blister rust may be limited to the warmer and wetter areas of the Far North.
This project is 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.