Weed Potential 

As a weed Purple Plague has been distributed throughout the world as an ornamental foliage plant. It was introduced into to Tahiti in 1937 and now dominates over 65% of the island forests covering over 70,000 ha with over 25% as monotypic stands and has infested neighbouring islands. It was also introduced into Hawaii in 1961 and by 1990 it had formed pure stands that spread up to 30 km from the point of introduction and is now infested three of the neighbouring islands. 

Other regions where the plant has naturalised include Granada, Jamaica, New Caledonia and Sri Lanka. it is also found in Northern Queensland, Australia where it is in its early stages of development and is predicted to form extensive pure stands tropical and subtropical forests. 

It was declared a noxious weed in 1997 and an eradication programme was set in place and is still running. In its native habitat it grows in areas with an annual rainfall of 2000 mm and an average temperature of 22°C however in countries where it has naturalised it tolerates much lower rainfall and cooler temperatures.

Miconia calvescens is an invasive noxious weed that can tolerate low light conditions and can invade undisturbed rainforest regions or disturbed ground where it cuts out light with its overlapping foliage to any native seedlings and smothering existing shrubs. It produces more than 5 million seeds per plant annually and they stay viable in the soil for up to 8-years and it has been recorded that the soil seed-banks can contain 50,000 seeds per square metre. Seed dispersal can include wind and water or rodents, cattle and pigs. They are also disbursed on mud that it adheres to vehicles or shoes and birds that can transport the seeds some distance from the parent tree.

Control methods included physically cutting trees down and treating the stumps with glyphosate or triclopyr. Smaller plants less than 3 m tall can be pulled out by hand including the roots.  Advantageous roots may sprout new plants but is rare. Remote infestations can be sprayed using a helicopter but has the adverse effect of millions of seedlings appearing in exposed ground.  

A follow-up spray is required and areas should be monitored for two years.  Biological control includes each introduction of fungi, weevils, leaf eating beetles and butterflies and moths.  The Chinese rose beetle proved to be the most efficient by default adding the plants but did not cause tree mortality.

One of the difficulties with this plant as a weed is locating it in dense rainforest particularly on steep terrain over a large area.  Successful control of this plant in infested regions is feasible provided annual funding is available.