Names like Water Celery and Vietnamese Parsley may sound exotic but they are actually nasty invasive pest plants that are choking some of our waterways around Richmond.
These pest plants form dense mats that block sunlight and deoxygenate the water, smother indigenous plants and trap sediment, and reduce habitat for stream life, including fish, eels (tuna) and macroinvertebrates.
Choked streams can also worsen flood impacts, threatening infrastructure such as bridges and pathways.
Water Celery is mainly a problem in waterways in the southeastern foothills down into Borck Creek, while there are pockets of Vietnamese Parsley in several other areas including near Washbourn Gardens.
Over the next few months, we will be running a spray programme as we fight to beat this growing problem.
National Institute of Water and Atmospheric Research (NIWA) has advised that herbicide application is likely to be the most successful control technique and has the potential to eradicate infestations over time.
NIWA recommends the use of Triclopyr triethylamine, also known as Garlon 360, because it is selective for the target weeds, and doesn’t persist in the environment. It readily degrades in water and soil and has low toxicity to fish, aquatic invertebrates and even humans. Nelson City Council reports success using it.
That said, we don’t recommend eating or using these weeds for cooking, firstly because they may have been sprayed, and secondly because picking them from the waterways can help them spread further, as they can grow from broken-off segments.
Our spray programme is scheduled to begin within the next couple of weeks.
