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Monitoring results have shown an incredible success rate for arum lily control – giving new hope to landholders who are controlling infestations on their properties.

Staff from Nature Conservation Margaret River Region and volunteers have been studying a control site at Point Rd in the Boranup forest in the Leeuwin-Naturaliste National Park, conducting detailed surveys every year since work started in 2019. The area was heavily infested with dense patches of arum lilies and threatening to spread further into the forest. The results show that even one year after control, impressive numbers of native plants emerge and leave no doubt about the effectiveness of control.  After two years, more native plant species were seen and the diversity of the understorey vegetation continued to improve year by year with on-going spot-spraying.

“The Point Road monitoring site shows that it’s not hard to control even large-scale dense infestations, and it allows the native bush to bounce back,” says Nature Conservation biodiversity officer Mike Griffiths, who coordinates the Arum Lily Blitz.

“In fact, the results were so positive that they surprised a lot of people.  People used to think it was too hard to control arum lilies and there wasn’t much point because the bush was already degraded once the arums had established. But this research shows that it’s not difficult to control arum lilies and that the bush has incredible resilience to bounce back once it’s given a chance.”

Vegetation transects showed an average 88 per cent reduction in arum lilies after the first year of control, and after a second year of control, the overall reduction in arum lilies jumped to an impressive 99 per cent. Control was done by contractors trained to work in environmentally sensitive areas using a selective herbicide that targets arum lilies and has little effect on most native plants.

Meanwhile, there was a smaller increase of 3 per cent in native vegetation after the first year, even with the depleted seed bank. But that jumped to an average of 23 per cent after the second year of arum control, showing that our native bush can come back after arums are removed.

“The results from Point Road are amazing. It’s astounding how resilient our bush is,” Mr Griffiths says. “These results are encouraging for landholders across the region who have joined the Arum Lily Blitz. If you can control arums across 30 hectares of forest and watch it steadily recover and improve, you can do it in your backyard.  It shows that it’s achievable.  It may be a big job in the first year or two, but after that, it gets much easier as long as you don’t take your eye off the ball! There will always be a few arums popping up as long as they’re in the neighbourhood, so you have to stay vigilant, but it gets easier and easier.”

Nature Conservation ambassador and local flora author Jane Scott has been busy spraying arums this season with the Friends of the Cape to Cape Track. She said that a lot of work was being done to tackle the invaders and to slow the spread of arum lilies. “After this season’s efforts, I think we’re going to see quite a marked improvement in more areas,” she said.

Landholders Drewe and Elma Vincent have 168 acres on Redgate Rd and said the improvement of their 1 km arum-infested creek line was “magnificent” after three years of control work by themselves and contractors. “It was a heavy infestation. At the head of the creek, the infested area was probably 100m wide. It was thick with arum lilies. You couldn’t even see the water in the creek,” said Mr Vincent. “Now, there’s virtually no arum lilies in the creek line. I’ve been surprised by the success. It’s been magnificent. We’re very, very happy.”

He added: “Now the arum lilies are gone, we’re hoping for the native trees and understory to come back. It’s a bloody hard job for the contractors in that rugged area but they do an amazing job. We really hope the message continues to spread because everyone needs to get on board.”

Mr Griffiths said that the early onset of warm, dry weather has shortened the spraying season, but said that arum lilies could still be controlled in some areas if the leaves are green and the seed heads haven’t fully developed. “It may not be too late to undertake control, especially if the arum lilies are in shaded, damp areas,” he said. “It’s also a great time to plan ahead for next year, to read up on practical control measures and work out if you need contractor help in 2024.”

Arum lilies are an introduced species from South Africa and are one of the major threats to biodiversity in our region. They outcompete the unique native flora and degrade crucial wildlife habitat.  But the Arum Lily Blitz has been hitting back with a coordinated region-wide attack on arums, funded by the WA Government’s State Natural Resources Management Program until 2024.

If you plan to undertake arum lily spraying, there are a wealth of resources including a spraying video tutorial at Landholders can sign up to the Blitz to receive free herbicide, information and resources and contractor recommendations.