The family Melastomataceae is represented in Hawai‘i entirely by alien species, introduced for their ornamental appeal. Many members of this family have the "exotic" features of attractive foliage and/or showy flowers and at first appear to by desirable for landscaping. However, the majority of these species have proven to be invasive and highly disruptive to native systems. They are now considered serious noxious weeds wherever they have been introduced in Pacific islands, including Hawai‘i. Further introduction of any member of the Melastomataceae to Hawai‘i is now prohibited.
A large leaf of Miconia calvescens,
showing the purple undersurface and prominent veins that contribute its ornamental appeal
as an "exotic" plant.
Miconia calvescens, native to the Neotropics, usually occurs in Hawai‘i as a small to mid-sized tree, having escaped cultivation where it invades, and threatens to invade intact native forests, forming thickets and excluding all other vegetation. This species has severely invaded the forests of Tahiti, causing extensive environmental damage. A concerted effort is currently underway to prevent the further spread of this species in Hawai‘i through public education, detection of populations, and eradication by mechanical removal and herbicide application by state, federal and private agencies and environmental organizations. Development of biological controls is also highly desirable and is underway. For this purpose, cooperative agreements have been established with scientists in Brazil for the detection and initial screening of potential biocontrol agents. A Brazilian plant pathologist, working with support from the Cooperative Park Studies Unit at the University of Hawai‘i, Hawai‘i Department of Agriculture plant pathologists, and myself, has identified several leaf-spotting fungi on M. calvescens and has sent some to Hawai‘i for host range testing under quarantine. Perhaps the most promising among these at present is a strain of Colletotrichum gloeosporioides that testing has shown to be specific to the target.
M. calvescens inoculated with Colletotrichum
gloeosporiiodes in quarantine in Hawai‘i.
Microscopic features of C. gloeosporioides:
setae (left), and germinating conidia (right).
Leaf spots on the upper (left), and lower surfaces (right) of leaves infected
with C. gloeosporioides. It is hoped that such infection will cause
defoliation.
A lower stem lesion (arrow),
caused by C. gloeosporioides, on M. calvescens in quarantine.
Permits for field applications of C. gloeosporioides recently have been issued based on positive results of testing in quarantine.
A stand of M. calvescens on the island of
Hawai‘i to be inoculated with C. gloeosporioides (left).
A formulation containing conidia of the fungus is sprayed on foliage with a power
sprayer (right).