By ANNASTASIA KAWI and WAREA ORAPA of NARI
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| Siam weed affected and its growth stunted by Gall Fly - an example of successful bio-control of invasive weeds in PNG |
Weeds cause serious obstructions to land use systems
worldwide.
Many introduced weeds are serious impediments to agriculture
productivity by causing significant production loss and threat to food
security.
These impediments pose immense challenges to farmers and other
land users.
Managing these weeds
is a critical defy in any attempt to get the maximum output.
And Papua
New Guinea is no exception!
While plantation agriculture and some subsistence or
semi-subsistence farmers generally use physical and chemical control measures
to reduce the negative impacts of weeds in PNG, the use of bio-control methods
has been significantly effective in managing some introduced and invasive weed
species.
Bio-control, or biological control, of weeds is defined as
the use of host-specific natural enemies such as herbivorous insects and mites
or disease causing plant pathogens for the regulation of the population of
weeds.
Papua New
Guinea agriculture is still reliable on
manual labour for weeding.
Cultural methods are also used to suppress weeds.
The use of
herbicide and manual means (such as hand-pulling) is practical only in very
limited situations such as small subsistence food gardens.
In smallholder semi-subsistence farming
situations, it becomes necessary to employ chemicals with large numbers of
labour.
These conventional methods of control are not
practical as they are costly, time-consuming and often labour-intensive.
In natural
systems where farming is not important, but weeds are a threat to ecosystems or
the survival of important native species of fauna and flora, such control
measures are not feasible at all.
Bio-control
is seen as the only sustainable and cost-effective means to control introduced and
invasive weeds, both in production areas (agricultural, forestry and fisheries)
and natural areas (natural ecosystems such as rivers and rainforests).
Once
released and established in an area, a bio-control agent can take two to six
years before the benefits are measured.
When it
works, bio-control is permanent, cheap and self-sustaining, requiring very
little or no intervention in the long-term as the weed and bio-control agent
reaches a point where they regulate each other’s population.
In PNG,
there have been 15 bio-control agents introduced for weed control compared to
42 species of parasitoids for insect pest control and four against snail pests.
Generally,
weed bio-control has been more successful in terms of establishment and control
of the target weeds compared to the effectiveness of bio-control agents used against
arthropod pests and snails.
The high
level of success of weed bio-control maybe attributed to the fact that
successful host-specificity research was done elsewhere before importing into PNG
for local use.
Some textbook
examples of successful weed bio-control in PNG include the successful control
of salvinia (Salvinia molesta) and water
hyacinth (Eichhornia crassipes) in
the Sepik River, the recent control of Siam weed (Chromolaena odorata) in New Ireland, Sandaun and East New Britain and
the dramatic decline of the broomstick weed (Sida ) in the Markham Valley and Central province.
In the Sepik River
case, almost 250 sq km of water surface was covered with the floating fern salvinia,
directly impacting the daily livelihoods of river dependent villagers in the
late 1970s and early 1980s.
People were
not able to travel using canoes and even motorised boats suffered from
continuous entangling of the outboard motor and heavy fuel consumption in
heavily-infested situations. Fishing for protein became restricted and tourist access
to backwater villages was denied due to the thick blankets of floating salvinia
and the much larger water hyacinth in the 1990s.
With the introduction and release of a tiny
weevil called Cyrtobagous salviniae,
from the Amazon basin in South America where Salvinia originates from, the weed
population crashed from the high 250 sq km to a negligible 2 sq km within two
and half years!
Life
returned to normalcy for the people living along the river and others such as
tourists.
A lot of
awareness and publicity was made to the people along the Sepik River
and other affected areas in PNG have acknowledged the importance of biological
control.
Similarly,
the introduction and establishment of gall fly and Arctiid Moth have
contained the Siam
weed.
Currently, National
Agriculture Research Institute (NARI) is implementing a bio-control programme against
a major agricultural weed known as ‘Mile-a-minute’ (Mikania micrantha) in PNG and Fiji.
Funded by the
Australian centre for International Agricultural Research, the collaborative
programme involves the Secretariat of the Pacific Community (Fiji), Queensland Department of Primary
Industries (Australia), and PNG’s
Cocoa and
Coconut Institute and Oil Palm Research Association.
The
overall objective is to introduce bio-control agents to suppress the growth and
presence of Mile-a-minute
in order to minimise its impact on food security, income, and to increase
national and regional capacity to undertake future biocontrol programmes
against weeds.
One of the major activities of the project is to increase
awareness of the bio-control to the farming communities and the general public.
The bio-control agent used is a rust forming fungus called Puccinia spegazzinii which was supplied
to PNG and Fiji by the
Commonwealth Agriculture Bureau International, UK,
after having collected it from Eastern Ecuador in South America and testing in London.
The rust has been
released in 14 lowland provinces in PNG since early 2009.
Scientists are working with communities in observing the
progress.
Subsistence farmers and the commercial plantation sector can
anticipate a positive outcome as the control materialises in the near future.
Biological controls
have been proven to be cost-effective and sustainable means of managing weeds for
agricultural and land use systems and eventually enhance greater food
production and improved livelihoods.
