The original native range of hibiscus bur (Urena lobata) is uncertain with limited data suggesting Asia. The plant has been introduced to many countries including parts of North America, Africa, and the Pacific either accidentally or as a fibre crop.
The cotton-like fibre that surrounds the seeds has been used as an alternative to down as filling in mattresses, pillows, and upholstery etc, but it is difficult to spin, and synthetic fibres and jute are far more commonly used these days. Parts of the plant have also been used as traditional medicine for a range of ailments.
Hibiscus bur is now considered a serious weed in many places, such as Fiji, Vanuatu, Cuba, and the United States where it forms dense patches and monospecific stands.
Impacts
Hibiscus bur can rapidly colonise disturbed areas and is tolerant of a wide range of soil types and elevations. Pastures, grasslands, cane fields, plantations, gardens, roadsides, clearings and wasteland are all at risk of invasion by this shrub impacting food security. In Vanuatu it is estimated that a third of pasture is currently lost to this weed.
The impacts of hibiscus bur are expected to increase in the future, as it continues to spread and colonize new areas. Hibiscus bur’s ability to thrive in a variety of soil types and climatic conditions makes it particularly well-suited to take advantage of changing environmental conditions, including those caused by climate change.
Controlling the problem
Controlling hibiscus bur is a time-consuming and expensive process. Herbicides can provide good control but are often too expensive and there is potential for harm if not used safely. Mechanical control appears to be less effective and requires expensive equipment. Hand pulling is restricted to small plants so often impractical. However, a new approach involving natural enemies now offers some hope for controlling hibiscus bur.
A leaf-feeding lace bug (Haedus vicarius) is being deployed in the Pacific which is expected to be able to provide effective control of this weed as it can severely damage this plant.
Hibiscus Bur Lace Bug (Haedus vicarius)
A leaf-feeding lace bug from Malaysia was ntroduced to Vanuatu in 2024 to control hibiscus bur (Urena lobata). This is the first time this lace bug has been used anywhere in the world against hibiscus bur. The lace bug may also eventually be released in other parts of the Pacific where this weed is a problem.
How would I recognise the lace bur and what is its lifecycle?
The adults are 2-3 mm long with lace-like wings that have darker brown markings, and they are shaped a bit like a fish. The nymphs are dark-coloured and covered in pale spines. They develop through 5 instars or growth stages. Nymphs and adults are typically found on the leaf surface. Nymphs feed gregariously around the location where they hatched and will disperse once they reach adulthood. The adults are slow-moving but can fly when provoked.
Females produce on average about 180 eggs each. The tiny eggs are implanted in the leaves on the lower surface and are not visible to the naked eye. It takes about 3 weeks for an egg to hatch and develop into a fully-grown adult. Once fully mature, males live for another 20 days and females live for around 40 days.
How does it damage hibiscus bur?
The adults and nymphs feed on the leaves by inserting their needle-like mouthparts into the leaf tissue and sucking out the fluids. This creates small yellow/white spots on the upper surface of the leaf. When feeding damage is heavy the leaves turn yellow and die. In Malaysia the greatest damage is seen from March-July.
Will it attack other plants?
During testing only one other plant species supported full development of the lace bug: Malvaviscus arboreus (an introduced ornamental plant in Vanuatu). However, it is a suboptimal host so lace bug populations cannot be sustained on it.
Minor adult feeding occurred on a few other plant species during no-choice testing: Hibiscus tiliaceus (a native plant), Sida rhombifolia (an introduced weed) and Abelmoschus esculentus (okra). Minor spill-over attack may occur on these species if high numbers of lace bugs are dispersing from nearby heavily damaged hibiscus bur plants in search of food. However, these species also occur in the native range of the lace bug and there are no records of the lace bug ever attacking them, so the test results may overestimate the risk.
Moreover, any non-target impact, if it occurs, will decline over time as hibiscus bur is brought under control and lace bug populations decline accordingly.
Manaaki Whenua technicain Stephanie Morton collects lace bug burs ahead of their transfer to Vanuatu
