International Postgraduate Intern
Daniel Perlaki is working with Rainforest Rescue to ensure that international
best practice is helping underpin invasive weed management.
As part of his
research the controversial issue of the use of Roundup has been raised; Dan
talks further about the issue…
If you would like to discuss Dan's reseach please contact him by email or 1300 763 611
glyphosate – the active ingredient in Roundup (the world’s most widely used
chemical herbicide) – was within hours of recall from shops due to a ruling by the European Commission. Only at the last minute and under threat of a lawsuit
from the manufacturer Monsanto was it given a temporary reprieve and an extension
to continue production. By the end of 2017 a report from the European Chemical
Agency will determine whether glyphosate is safe, and whether its production
and use will be allowed in Europe. Last year, areport by the World Health
Organization’s International Agency for Research on Canceridentified high
doses of the herbicide as a “probable carcinogen” sparking fierce debate on its
use in agricultural systems. There is also controversy over glyphosate’s impacts
on the wider environment with the chemical being implicated in the decline of
earthworms (1), soil microbial communities, butterflies (2) and amphibians (3).
weeds are a serious contributor to animal and plant extinctions worldwide (4).
They can influence nutrient cycles and fire regimes, can outcompete native
flora, and cause landscape and evolutionary scale changes. Effective management
and control of weeds is crucial to maintain the health of rainforests and
protect their unique biodiversity. The current research project at Rainforest
Rescue is evaluating weed control methods to ensure compliance with
international best-practice. An important element is learning from, and sharing
knowledge with, other organisations working with similar issues. Rainforest
Rescue has a clear responsibility to ensure that control methods are
underpinned with the best scientific information and minimise harm to the
environment and native flora and fauna.
Over the past 45
years glyphosate use has been growing, not only in food production, but also in
conservation actions including ecological restoration projects (5). Due to limited
funding and resources, conservation and restoration organisations often can’t
employ enough people to manually remove weeds at the scale required. Even if
money and time weren’t an issue, manual weed removal can be ineffective and
sometimes counterproductive (5). As such, the cost and time effective nature of
using glyphosate can be appealing (5). There are many different methods by
which glyphosate can be applied to weed species depending on the characteristics
of the plants. Some methods include precision application and have little reported
impact on the surrounding environment. However, more significant impacts can arise
when broad-scale spraying is used as this can result in excess glyphosate entering
the soil or reaching non-target species.
containing herbicides are often advertised as becoming inactive in the soil
very quickly due to their ability to bind to soil particles. However, the
breakdown of the active chemical (N-(phosphonomethyl)glycine)
can be delayed as this process is dependent on the presence of specific soil
bacteria (6). Other additives present in the solution aside from the active
ingredient (known as surfactants) can also cause unintended harm to non-target
species and the wider ecosystem (7). The problem can be further exacerbated
when the volumes of herbicide applied are not regulated, as is often the case
with backpack sprayers. In a significant number of cases more glyphosate than
is needed is applied, which subsequently can drip off the leaves of the target
species and soak into the soil (8). In addition, when glyphosate breaks down its
primary metabolite is also toxic to plants (9).
is a complex issue, and the methods for controlling and supressing weeds needs
to reflect that. Glyphosate has become a problem due to many people considering
it as a one-size-fits-all approach to controlling weeds. As a result of its
over-use, glyphosate residues are now found in a startling proportion of the
produce we eat and drink and its impact on natural systems can be
significant. Weeds can also evolve to become tolerant of glyphosate, so land
managers need to ensure that they have alternatives available. In general,
a shift to a more integrated weed control system with a variety of control
methods is needed, both in farming and in habitat restoration. No one method is
appropriate for controlling weeds everywhere, and Rainforest Rescue is looking
to lead by example by proving that habitat restoration doesn’t need to be
dependent on glyphosate.
The initial desk
top and stakeholder research has shown that Rainforest Rescue’s weed control
methods are in accordance with other environmental groups working in similar
areas. They are diverse and adaptive, depending on the situation and what kind
of control is required. It is Rainforest Rescue policy to err on the side of
caution – while the jury is still out on the health and environmental impacts
of chemical herbicides like glyphosate, we will actively pursue alternative
weed control methods that do not use them.
To further this
agenda Rainforest Rescue is looking into the efficacy of a whole host of
non-herbicide based methods, as well as methods that reduce the amount of herbicides
used to control weeds. Depending on the circumstances at a site, alternative
practices that have been used or considered include residue mulching to supress
weed germination, the use of living mulches, and supporting soil microbial
communities which favour native woody species. Using naturally competitive
native plants to displace weeds is Rainforest Rescue’s favoured approach.
factor in that approach is the density of tree planting used by Rainforest
Rescue. By planting trees at a high density the tree canopy closes quickly,
shading the ground and making it unsuitable for light dependent weeds. In the
Daintree the rate of tree growth in reforestation projects means that weed
management is only an issue in the first couple of years. Rainforest Rescue
plants a significant range of species in reforestation projects, and these are
supplied from local seeds propagated at the Daintree Native Nursery. This approach
not only helps to restore plant diversity and improve weed management, but also
includes the growing of species that are a food source to attract birds,
mammals and other wildlife back to the areas. The wildlife then disperse seeds
back into the plantings, further increasing the number of trees.
(1)(1) Gaupp-Berhausen, M., Hofer, M., Rewald, B. & Zaller, J. G. (2015) Glyphosate-based herbicides reduce the
activity and reproduction of earthworms and lead to increased soil nutrient
concentrations. Scientific Reports; 5:
(2)(2)Pleasants, J. M. & Oberhauser, K. S. (2013) Milkweed loss in agricultural fields because
of herbicide use: effect on the Monarch butterfly population. Insect
Conservation and Diversity; 6(2):
(3)(3) Ralyea, R. A. (2005) The lethal impact of Roundup on aquatic and terrestrial amphibians.
Ecological Applications; 15(4):
(4)(4) Clavero, M. & Garcia-Berthou, E. (2005) Invasive species are a leading cause of
animal extinctions. Trends in Ecology and Evolution; 20(3): 110.
(5)(5) Kettenring, K. M. & Adams, C. R. (2011) Lessons learned from invasive plant control
experiments: a systematic review and meta-analysis. Journal of Applied
Ecology; 48(4): 970-979.
(6)(6) Fan, J., Yang, G., Zhao, H., Shi, G., Geng, Y.,
Hou, T. & Tao, K. (2012) Isolation,
identification and characterization of a glyphosate-degrading bacterium,
Bacillus cereus CB4, from soil. Journal of General and Applied
Microbiology; 58(4): 263-271.
(7)(7) Tsui, M . T. K. & Chu, L. M. (2003) Aquatic toxicity of glyphosate-based
formulations: comparison between different organisms and the effects of
environmental factors. Chemosphere; 52(7):
(8)(8) Cornish, P. S. & Burgin, S. (2005) Residual effect of glyphosate herbicide in
ecological restoration. Restoration Ecology; 13(4): 695-702.
(9)(9) Reddy, K. N., Rimando, A. M. & Duke, S. O.
(2004) Aminomethylphosphonic Acid, a
Metabolite of Glyphosate, Causes Injury in Glyphosate-Treated,
Glyphosate-Resistant Soybean. Journal of Agriculture and Food Chemistry; 52: 5139-5143.