Investigating two different mechanical control options for naturalised population of Hydrocleys nymphoides in South Africa

Investigating two different mechanical control options for naturalised population of Hydrocleys nymphoides in South Africa 
Menzi Nxumalo, Reshnee Lalla
Invasive Species Programme, SANBI

Hydrocleys nymphoides, an aquatic plant native to South America, has demonstrated invasiveness in several countries. In South Africa, its distribution is limited to one naturalized population, recently detected in a dam in the KwaZulu-Natal Midlands region. Plants were observed growing mostly along the edges of the dam, occupying about 30% of this 23 400 m2  water body. Due to the multiple domestic and agricultural uses of the dam, the use of herbicides as a control option was not feasible and other control methods had to be investigated. This study aimed to compare two different mechanical control options that are recommended for aquatic systems used for domestic purposes. The first entails physically removing all parts of the plants using an aquatic rake, and the second is a plant shading method in which target plants are covered with black plastic that provides 100% shade cover. Here we report on the experimental set up and provide detailed information on the pros and cons of both control options. This study aims to reduce the current infestation size of H. nymphoides, prevent spread to other water bodies, and inform broader management options for this species and other similar aquatic invasive alien plants in South Africa.