Adventure Sport

Dusi wins hyacinth battle

2012-02-09 21:53
The headwater of Inanda dam clear of water hyacinth (Gameplan Media)
Pietermaritzburg - With a week to go before the start of the Unlimited Dusi canoe marathon, the race has won a critical victory over water hyacinth that was choking stretches of the race course, threatening to force paddlers to carry their kayaks for kilometres around the infestations of vegetation in the river.

The Department of Water Affairs' Working for Water programme in conjunction with the Dusi uMngeni Conservation Trust (DUCT) put in place a ground-breaking strategy to deal with hyacinth blockages at two key areas on the race route - above Inanda dam and the lower Umgeni above the Outer Ring Road.

Both required different approaches as the ecological demands of the two regions differed widely.

The lower uMngeni hyacinth, Limpopo grass and water lettuce blockage was stopped in the final quarter of last year and eradicated using spraying that started during last year's Dusi and mechanical means, primarily a specialised Truxor DM 5000 water tractor imported for the purpose, with the support of the Durban Green Corridor initiative.

However the most dramatic inroad into the infestation was in the massive blockage above headwaters of Inanda dam, held in place by a boom preventing the exploding mass of hyacinth and water lettuce from extending onto the dam.

In December paddlers taking part in the Land Rover Hansa 50 Miler had to carry their craft for nearly 2 kilometres before the river at Mbeje's Store was choked with water hyacinth and water lettuce.

In what is being described as a triumph for biocontrol, the DUCT and Working for Water team introduced thousands of weevils onto the vegetation mass in the latter stages of last year, when the warmer summer temperatures triggered exponential growth of hyacinth and water lettuce.

"The weevils feed on the buoyant leaves and eat into the stems where they lay eggs which hatch," said DUCT's Bart Fokkens. "The larvae then continue to eat into the plant mass until it finally sinks to the bottom of the dam."

It took less than six weeks, with the final spraying of herbicide helping to complete the eradication of the hyacinth and water lettuce," he added. "The experts who have been working on this for many years say they have never seen such a successful combating of hyacinth and water lettuce."

The weevils are bred at the SA Sugar Research Institute at Mount Edgecombe to handle both waterborne and terrestrial weeks.

The DUCT team is currently involved in a massive clean-up of the Lower uMngeni. On Wednesday they moved over 900 plastic bags of litter from the area, and have gradually started moving further upstream to continue the clean-up.

The Unlimited Dusi canoe marathon from Camps Drift, Pietermaritzburg to Blue Lagoon, Durban takes place on 16-18 February 2012. More info can be found at

The before picture. The headwater of Inanda dam choked by water hyacinth and water lettuce eight weeks ago. (Gameplan Media)


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