George Dam – Kariba Weed Biological Control

Issued George Municipality, 22 February 2022

The George Municipality continues to address the Kariba Weed found at the at the Katriver inflow of the Garden Route Dam. During the first week of February 2022, Petrus Crous, an Outeniqua Canoe Club member (OCC) and Tyrone April (Superintendent Parks: George Municipality) released a thousand Salvinia weevils (Cyrtobagous salviniae).

This is a follow up on the December 2021 release of approximately 1200 weevils at the Katriver inflow. The Salvinia weevils target the Kariba weed (Salvinia molesta), a free-floating invasive fern. The Salvinia weevils are a highly effective biological control mechanism of Kariba Weed. The adult weevils are 2mm long and black. Young larvae feed on the buds and roots while older larvae tunnel into the plant causing leaves to die back and drop off. Since the weevils eat the plant, a significant reduction in the amount of dead plant material is expected once the weevils have established.

Matthew Paper (Junior researcher, Centre for Biological Control (CBC) Department of Zoology & Entomology at Rhodes University) and Petrus Crous (OCC) surveyed the dam to assess the most recent distribution of the Kariba Weed. Prior releases have shown positive signs of Salvinia weevils causing Kariba weed dying back. To that end, the municipality continues to strengthen cooperation between all parties involved in the localised rearing facility that will ensure a stable supply of Salvinia weevils in future.

The management of the Kariba weed at the Garden Route Dam is an ongoing process and the municipality is continuously assessing the options available to control the spread and density.