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| Kunibert Tibil, District Administrator, Kavieng, New Ireland, holding dead stems of chromolanea with galls (photo: W.Orapa) |
Smallholder farmers in Papua New Guinea continue to benefit
from the introduction of a biocontrol agent of one of the world’s worst
weeds through a project funded by the Australian Centre for
International Agricultural Research (ACIAR).
By 1998, the weed chromolaena (
Chromolaena odorata) had
invaded many subsistence farms in PNG, smothering crops such as taro,
cassava and paw paw, along with plantation crops such as coconuts, oil
palm and cocoa.
Today, where farms and roadsides were once choked with the weed,
other useful plants are growing, and landholders, having saved countless
hours of weeding, have more time to grow more produce for food and
sale.
Gall fly effective
From 1998 to 2007, three biocontrol agents were introduced into PNG
through the ACIAR project led by Michael Day of the Queensland
Department of Employment, Economic Development and Innovation in
association with Warea Orapa and Ingu Bofeng of the PNG National
Agricultural Research Institute (NARI).
The gall fly (
Cecidochares connexa) proved to be the most
successful agent introduced.
It was released at over 350 sites in all
provinces where chromolaena occurred and established at 300 sites.
Following establishment, it spread naturally to a further 350 sites.
“The research showed that, as the number of galls created by the flies
increased, branches of chromolaena died, reducing biomass and flower and
seed production,” said Mr Day.
At the completion of the project, socioeconomic surveys of nearly 200
landowners found over 80% of respondents thought there was much less
chromolaena than before the gall fly was released.
About 70% said they
were benefitting from the control of the weed, with half saying their
weeding times were reduced, and control costs had fallen 45%.
ver 60%
said their crop yields and income had increased as a result of the
control of the weed.
Long-term benefits
Five years later, an adoption study recently published by ACIAR (
http://aciar.gov.au/publication/CP45)
found that the benefits of the project are continuing.
“Information on
chromolaena distribution and the status of the gall fly is still being
used by NARI officers to both check whether the gall fly is present and
to conduct opportunistic releases if the gall fly is not present,” said
Mr Day.
“Landowners report that the gall fly has made a substantial
difference and some are still moving the insect to new areas.
"Other
landowners are now reducing the level of burning or leaving patches of
chromolaena to ensure populations of the gall fly are maintained.
“Nearly 70% of landowners who had chromolaena on their farms reported
some benefits as a result of the gall fly.
"The major benefit has been
the reduced weeding time required to maintain food gardens, allowing
landholders to increase the size of their blocks, thus increasing yield
and income,” Mr Day said.
Regional differences
While chromolaena has been significantly reduced in most provinces
where it was present, there is variation depending on land use and
climate according to Mr Day.
“In New Ireland, where we first introduced the gall fly, there has
been very good control and socioeconomic impact studies suggested that
the landholders are benefiting,” he said.
“In the drier provinces, such
as Morobe, control is slower and less complete.
"In West New Britain,
which is considerably wetter than most other provinces, control has not
been as good and chromolaena remains a problem because the gall fly
needs sunny days with temperatures over 30 °C to mate.”
The benefits of this biocontrol project will continue to flow through
the community, with the gall fly suppressing populations of
chromolaena, spreading naturally throughout areas where the weed is
present, and being relocated by landowners into new areas as the weed
spreads.
International benefits
Through various international workshops and publications, the news of
the outcomes of the chromolaena biocontrol project in PNG has resulted
in other countries also introducing the gall fly.
Mr Day reports that
the gall fly was introduced into East Timor in 2005 and Thailand in
2009.
An application has recently been submitted to introduce the gall
fly into Kenya.
In addition, China, Taiwan and Palau have all expressed
interest in importing the agent.
Controlling chromolaena in neighbouring countries to Australia helps
farmers increase food security in those countries, reduces the risk of
the weed spreading to other neighbouring countries such as the Solomon
Islands thus reducing the risk of further spread into Australia, and
increases Australia's expertise in weed control.