White Shrimp plant spreads quickly
WHITE shrimp plant (Justicia betonica) is native to eastern and southern Africa and the Indian sub-continent (i.e. India and Sri Lanka).
In the book, World Worst Economic Weeds, a standard reference, there are nine species of the genus Justicia listed.
There are other shrimp plant species sold in the Australian plant nursery sector, such as the pink Mexican shrimp plant, Justicia brandegeeana, which is a native of Guatemala, Honduras and Mexico; Brazilian Plume Flower, Justicia carnea, and, Mexican Plume, Justicia fulvicoma.
All of these species are also becoming widely invasive in parts of the warmer coastal districts of Queensland and northern New South Wales due to garden waste dumping and natural seed spread.
White shrimp plant is regarded as an environmental weed in Queensland and as a potential environmental weed or "sleeper weed" in other parts of northern Australia and NSW.
The shrimp plant comes in a range of colours such as the pink form and is sold in plant nurseries as a garden plant and is often fund in dumped garden waste.
The shrimp plants have spread from garden cultivation and invaded roadsides, parks, urban bushland, disturbed sites and waste areas through dumped garden waste or the seeds being spread by animals, humans, vehicles, wind or water. It prefers damper sites and is particularly invasive along waterways and in riparian areas.
White shrimp plant is quickly becoming widespread and large populations are common along waterways in south-eastern Queensland, crowding out native plant species.
It forms dense infestations and was recently ranked among the top 200 most invasive species in Queensland.
This species was first recorded invasive in New South Wales in the year 2000, in Ukerebagh Nature Reserve at Tweed Heads in the far north-east corner of the state.
It is spreading south into New South Wales, particularly around urban areas where people have dumped it as garden waste.
White shrimp plant is a perennial soft-wooded shrub to 2.5m tall forming dense ground cover; stems rooting where they contact the ground, with dense bands of hairs at nodes, glabrous elsewhere.
Stems, often with a purple tinge, may be rough to the touch. Leaves are opposite, ovate to elliptical to 22cm long to 12cm wide, slightly wavy, upper surface dark green, lower surface paler; petiole up to 15mm.
Flowers in spikes, each subtended by three white bracts with prominent green veins. Corolla is two-lipped, mauve with a white spot on the lower lip; capsules two-lobed.
Flowers are white with tinges of mauve. Flowers in summer, followed by seeding in autumn.
Individual plants can be hand-pulled but will often break off at the nodes on the trunk. It also roots at nodes which touch the ground, so this can also make hand pulling more difficult. Most common herbicides (glyphosate products) used as a foliar spray will kill shrimp plants.
If weed control is necessary among desired garden plants, or native plants, dripping or painting herbicide onto the leaves can be effective. With larger infestations, cultivation is not recommended as this will encourage mass seed germination, and if near watercourses will encourage soil erosion and seed spread into water courses.
Article writer Ian Read can be contacted 07 4159 9365, or email ian.read7@bigpond. com.au for free weed identification and native plants advice, and for landscaping and weed control.
Phone Landcare president Michael Johnson on 0422 297 062 for weed project details and monthly meeting times, or email email@example.com
The Bundaberg Landcare Nursery at the Salvation Army Tom Quinn Centre, Doctor Mays Rd, is open on Wednesdays, Thursdays and Fridays, 10am-4pm for native plants