Impi's Water hyacinth Project

During National Water week on the 18 - 24 March, the Impi's and Lead Instructor Pieter Pretorius started the Water hyacinth project on one of the dams on the Bhejane property.

Water hyacinth (Eichhornia crassipes) is a perennial, aquatic plant, native to the Amazon Basin of

South America. It is a category 1 declared weed in South Africa and must be controlled, or eradicated where possible. In South Africa, water hyacinth was first recorded in 1908 when it was introduced into garden ponds. The rapid reproductive rate of the plant in conjunction with the activities of man and the absence of natural enemies has enabled the plant to invade water bodies throughout the country. In ideal conditions, the weed can double its population every 11- 18 days and seeds in the sediment may remain viable for up to 20 years.

Dense mats of vegetation can clog water systems, interfere with recreation and irrigation, promote siltation, exacerbate the effects of flooding and create anoxic water conditions which threaten biodiversity. Infestations could also create breeding habitats for disease- carrying organisms such as malaria mosquito's and the bilharzia snail. Water hyacinth is regarded as South Africa's most damaging aquatic weed and costs the country millions of Rands a year to try and control.

The Impi's first used the manual control of the weeds by removing it from the dam. This proved to be very labour intensive and with the rapid reproductive rate of the plants, will not prove to effective if it's not an ongoing daily project of removing these weeds.

Through some research Pieter found a possible solution for the control of these weeds; The Water hyacinth Mite and Mirid. These insects are the natural enemies of these plants and we managed to

obtain a few thousand of these insects and released them onto the weeds. These Mites (Orthogalumna terebrantis) and Mirid's (Eccritotarsus catarinensis) feed and lay their eggs in these Water hyacinth weeds. Mites will feed on the older weeds, and clear feeding tunnels can be seen on the leaves when held up to the light. They will lay their eggs in the younger plants. These larval and nymphal tunnels affect up to 90% of the surface area of the leaves and reduce the photosynthetic capability of the leaves and reduce the vigour of the plant.

The Mirid's feed on the leaves, causing yellowing/ browning of the leaves due to the extraction of chlorophyll. Mirid's however prefer only the mature stands of water hyacinth, where the leaves protect them from excessive cold and heat. 

The use of this method has proved very successful in parts of South Africa and under the right conditions no other control methods should be required. All the Mites and Mirid's have been released and we are keeping a close eye on the water body to see what effect they will have on the looming problem.

Thank you to Instructor Pieter and the Impi's for their hard work and we look forward to seeing the results in the near future! Keep following our Facebook page and blog for updates on the progress

made.

For additional information on the Water hyacinth and control methods,  visit the Agricultural Research Council Website: www.arc.agri.za