- Widespread. In Australia, and most Pacific island countries.
- Annual, or perennial, fast-growing, invasive weed of wetlands - streams, ponds, marshes, swamps, ditches. Weed of rice, taro, cocoa, coconut and sugarcane plantations, pastures, along roadsides. Roots grow from lower nodes and extensive mats develop.
- Stems hairy, green, reddish-brown, up to 3m, sometimes woody at base. Leaves, alternate, pear-shaped to oval (up to 15cm), hairy, short stalks. Flowers, terminal or from leaf axils, with four yellow, oval petals (10-20mm long), with leaf-like sepals beneath. Fruits long (20-45mm), brown, ribbed with sepals attached, containing many seeds.
- Spread: vegetatively on creeping stems that root; seed, possibly in water, or in mud on machinery/vehicles, footwear. Plant trade: used as an ornamental and in traditional medicines.
- Biosecurity: risk is unofficial introduction of seed and plants. Available on Internet. Check imported machinery/vehicles.
- Biocontrol: none.
- Cultural control: hand-weed; slashing; mulch (5-10cm) to prevent seedling growth; clean soil and seeds from machinery/vehicles; check clothing.
- Chemical control: In Australia, glyphosate registered as spot-spray for other Ludwigia species in semi-aquatic and aquatic situations. In Fiji, glyphosate, 2,4-D, dicamba, MCPA.
Pacific Pests, Pathogens, Weeds & Pesticides
Willow primrose (514)
Willow primrose. It is also known as false primrose, primrose willow, yellow willow herb, Mexican primrose-willow.
Ludwigia octovalis. It is a member of the Onagraceae. The plant is variable and several sub-species are recognised. Identifications require confirmation by a botanist familiar with the genus.
AUTHORS Grahame Jackson & Makereta Ranadi
Information from CABI (2015) Ludwigia octovalvis (primrose willow). Invasive Species Compendium. (https://www.cabi.org/isc/datasheet/31671); and Ludwigia octovalvis (Jacq.) P.H. Raven. PlantNET. New South Wales Flora Online. Australian National Botanic Gardens. (https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Ludwigia~octovalvis); and Fern K (2021) Ludwigia octovalvis (Jacq.) R.H. Raven. Tropical Plants Database. (https://tropical.theferns.info/viewtropical.php?id=Ludwigia+octovalvis); and from Ludwigia octovalvis (2021) Wikipedia. (https://en.wikipedia.org/wiki/Ludwigia_octovalvis). Photo 1 Tau'olunga (2007) Ludwigia octovalvis, (loaano) in a Tongan swamp. (https://commons.wikimedia.org/wiki/File:Ludwigia_octovalvis5.jpg). Photo 2 Gerald McCormack. Cook Islands biodiversity. (http://cookislands.bishopmuseum.org/). Photo 3 Forest and Kim Starr. Ludwigia octovalvis (flowers and leaves). Location: Maui, Kanaha Beach. (https://commons.wikimedia.org/wiki/File:Starr_070413-6937_Ludwigia_octovalvis.jpg).
Produced with support from the Australian Centre for International Agricultural Research under project HORT/2016/185: Responding to emerging pest and disease threats to horticulture in the Pacific islands, implemented by the University of Queensland, in association with the Pacific Community and Koronivia Research Station, Ministry of Agriculture, Fiji.