Page 14 - Landscape-Issue144

FEATURE

Distressed water lettuce impacted
by Neohydronomus affinis

RAND WATER APPOINTS CENTRE FOR

BIOLOGICAL CONTROL TO ASSIST WITH

BIOCONTROL ON VAAL RIVER BARRAGE

The Department of Water and Sanitation (DWS) has appointed Rand Water (RW) as
the implementation agent for the integrated control and management of invasive
alien plants (Pontederia crassipes – water hyacinth and Pistia stratiotes - water
lettuce) on the Vaal River Barrage Reservoir (VRBR). Rand Water has appointed a

Centre for Biological Control to assist with the biocontrol of these plant species,
both of which are extremely invasive, with water hyacinth being more resilient and
aggressive than water lettuce.

n early 2024, an “explosion” of growth present in the water. It was also identified well as three community sites. Funding for
of these two species took place on the that in order to undertake this work, an community rearing sites has come directly
IVRBR, fuelled by the “perfect storm”, integrated approach was required. The from community members themselves. All
namely spills of effluent-filled water rich integrated approach adopted includes rearing sites are already in full swing, with
in nutrients, hot summer conditions, the use of various mechanisms: physical agents being reared for both water lettuce
and reduced water flows in the system. removal, chemical spraying, curtaining in and water hyacinth.
At the peak of the spread, water surface the water course and biocontrol agents. The aim, where possible, is to use
cover had reached approximately 397 of The CBC is the only institution in South biocontrol agents for most of the control
a total 940 hectares monitored under the Africa equipped with specialist qualified of these two invasive alien plants, together
contract. staff, biocontrol agent rearing facilities, with physical removal; where other
At the time, due to huge public and and a network of teams available to methods are not working fast enough,
local community involvement with provide on the ground assistance in the approved herbicide application will be
physical removal, and pro-bono assistance form of advice, implementation support used. All biocontrol agents released have
from the Rhodes University’s Centre for and long-term monitoring techniques. been rigorously tested and confirmed to
Biological Control (CBC), the mass was As a result, Rand Water has appointed be host-specific before being approved
reduced to less than 100 hectares. Further the CBC as the sole service provider for for release in South Africa. This means the
work was undertaken by RW under the the upcoming season, to assist in all agents solely feed and complete their life
contract from DWS to physically remove aspects relating to biocontrol and provide cycles on their target host plants.
further plants over the winter months support for the project. The CBC team is Four biocontrol agents will be the main
when the plants are dormant. Cover is being led by Prof. Julie Coetzee and Dr focus of the rearing facilities: the water
now sitting at less than two hectares, as Kelby English, with additional support lettuce weevil Neohydronomus affinis,
at the end of spring. from Prof. Martin Hill. the water hyacinth hopper Megamelus
From the start of the project, it was Through the approval of the Department scutellaris, and the water hyacinth weevils
identified that the work would have to of Forestry Fisheries and Environment Neochetina bruchi and N. eichhorniae. In
be long term due to the nature of these (DFFE), four permits have been granted to South Africa, the water lettuce weevil
plants and the seed bank that was already rear biocontrol agents at the RW nursery as was first released in 1985 and the first

12 Landscape SA • Issue 144 2024 Check us out www.salandscape.co.za