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< prev - next > Natural resources management KnO 100372_Water hyacinth control (Printable PDF)
Water hyacinth
Practical Action
the weed and the result of these problems is more often than not a reduction in catch
and subsequent loss of livelihood. In areas where fishermen eke a meagre living from
their trade, this can present serious socio-economic problems. Fishermen on lake
Victoria have also noted that, in areas where there is much water hyacinth infestation, the
water is ‘still and warm and the fish disappear’. They also complain that crocodiles and
snakes have become more prevalent.
Reduction of biodiversity. Where water hyacinth is prolific, other aquatic plants have
difficulty in surviving. This causes an imbalance in the aquatic micro-ecosystem and
often means that a range of fauna that relies on a diversity of plant life for its existence,
will become extinct. Diversity of fish stocks is often effected with some benefiting and
others suffering from the proliferation of water hyacinth. People often complain of
localised water quality deterioration. This is of considerable concern where people come
to collect water and to wash.
Quantification of the problem is often extremely difficult. The real effect on fish stocks and flora
is unknown. It is hard to calculate the effect on fishing communities. Even quantifying the
coverage of the weed is difficult on bodies of water which are as large and geographically complex
as Lake Victoria. Satellite methods are the only accurate way of determining the spread of the
weed. Success is hard to measure when the exact scale of the problem is not clearly defined and
is anyway growing rapidly.
In many areas of the world few
studies have been carried out to
quantify the basic effects of the
growth of the weed on the
surrounding communities and
environment. This causes
problems when trying to
evaluate the scale of the
problem, possible ways of
combating its proliferation and
the impact that any control or
management programme may
Figure 3: The scale of the problem is considerable
©Paul Calvert/Practical Actioin
Control of water hyacinth
There are several popular control mechanisms for preventing the spread of, or eradication of,
water hyacinth. The 3 main mechanisms used are biological, chemical and physical control.
Each has its benefits and drawbacks. Chemical control is the least favoured due the unknown
long-term effects on the environment and the communities with which it comes into contact.
Physical control, using mechanical mowers, dredgers or manual extraction methods, is used
widely but is costly and cannot deal with very large infestations. It is not suitable for large
infestations and is generally regarded as a short-term solution. Biological control is the most
widely favoured long-term control method, being relatively easy to use, and arguably providing the
only economic and sustainable control. Below we will briefly discuss each of these methods.
Biological control
Biological control is the use of host specific natural enemies to reduce the population density of a
pest. Several insects and fungi have been identified as control agents for water hyacinth. These
include a variety of weevils, moth and fungi. Biological control of water hyacinth is said to be
environmentally benign as the control agents tend to be self-regulating. Control programmes are
usually inexpensive due to the fact that the control agents are known and only a small numbers of
staff are required to run such programmes. One major drawback is that it can take a long time to