Landcare Agony Aunt: some seasonal advice for your Landcaring questions
Dear Agony Aunt,
Our Landcare group has a beautiful wetland on our work site. Last year we noticed a pretty, yellow flowering plant along its margins and along the banks. It looked like a native so we let it be. This year however, the pretty yellow flowering plant is everywhere! It’s growing amongst the rushes and now that the water level has dropped, it’s really dense for about 2m into the wetland. The wildlife are losing their swimming and nesting spaces. How do we get rid of it?
Yours, concerned Wetland Warrior
Dear Wetland Warrior,
It sounds to me like you have an infestation of Long-leaf Willow Primrose, a common invasive wetland weed from South America. It forms dense stands in still or slow-moving water, clogging waterways, out competing natives and reducing habitat and food for aquatic animals.
It’s currently in flower and setting seed so it’s a great time to identify, treat it and get it under control. There are a number of weedy exotic Ludwigia but the common one in the Hunter is Ludwigia longifolia (Long-leaf Willow Primrose). It’s an upright annual shrub, growing tall and skinny, up to 3m and grows in shallow water and riparian zones. It has long, thin leaves with a pointed tip and a reddish stem. Its bright yellow flower makes it easy to spot, as you have found. We also have a native Ludwidgia in the Hunter, so make sure you ID them correctly. Ludwigia peploides is prostrate so it’s easy to distinguish from the tall and upright L. longifolia.
The best approach for control is firstly removing seed heads and disposing of them in your rubbish bin. The seeds are abundant and dust-like with high germination rates so it’s important to reduce seed drop. Plants can either be hand weeded, making sure you remove the root system or for larger infestations, spray with an aquatic-safe herbicide. All hand weeded material needs to be disposed of away from a water body to prevent reinfestation. Follow up treatment is crucial to ensure you treat new growth and don’t let it flower and seed again.
Check out DPI NSW Weedwise for more info. on identification and control. Here is the link: https://weeds.dpi.nsw.gov.au/Weeds/Longleafwillowprimrose
