Opinion
The weevil that can control Lake Kyoga weed
Publish Date: Apr 24, 2014
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By Brenda Mirembe

Over the past weeks, the media has been awash with an invasion of a strange weed on Lake Kyoga. The fast growing aquatic fern, Giant salvania (Salvinia molesta), which has massively spread on the Lake is characterised by forming dense mats, brown, yellow or green in colour.


Within a week under right circumstances, the weed, due to its rapid multiplication rate, can double in volume thereby clogging water ways and covering up the entire surface of the lake. It can inhabit many water environments including streams, rivers, ponds, aquariums, wetlands as well as rice fields.

The stealthy invader is very problematic to humans and the ecosystem due to its thick mats on water thus, hindering activities like agricultural irrigation, water transport, fishing and power generation. It can also deplete the oxygen source in water and block sunlight needed by aquatic organisms like fish and insects, among others.

It also acts as a haven for mosquitoes, snakes, crocodiles and others which are a threat to human health and physical wellbeing.

The weed is known to be spread by boaters from site to site since it hitch-hikes on boats. The young and even just small fragments of the weed may travel naturally in moving water and establish colonies wherever they settle. In other cases, the weed might be recklessly dumped in water by humans out of ignorance; unaware of the consequences of their actions.

The Government and relevant ministries, especially those of environment; and fisheries should act to stop the further multiplication of the weed to other water bodies before it is too late. This weed on Lake Kyoga was sighted a year and half ago when it was in its premature stage and somehow, concerned authorities became reluctant since it did not seem alarming and now it is colonising and covering the lake surface at a prolific rate as shown by images in an in the New Vision of March 27, 2014.

This time, looking to other countries like Egypt to come to our rescue may not be the best option. Though yes, fine they might wish to help but do we only have to rely on them? We should simply look for all possible means of eradicating this weed in its nascent stage of colonisation.

Biological control with a weevil named Cyrtobagous salviniae is possible. This weevil, which can be obtained from the Agricultural Research Service (ARS) in the United States Department of Agriculture (USDA), is well known for reducing and completely checking Giant Salvania weed.

It has been used in several countries like Austria, Zimbabwe, New Zealand, Zambia, New Guniea and others attaining great  success. Also using Salvinia grasshopper, Water lettuce moth and others can be effective since they also control other invasive water weeds including water hyacinth.

In case the weed has spread to water bodies in your areas in small infections, it is not a decorative species as most of you might think and take it to be a catalyst in cleansing water. In the absence of the scientific means proposed above, you can eradicate it by using hands to remove it from water, dry and then burn. It is not proper to re-deposit or release it to other water sources and the wild since they will re-grow.

We should come together and save our environment.

The writer is with Jane Goodall Institute (JGI) Uganda

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