Weeds, weeds everwhere!

Salvinia and hyacinth are growing profusely on the Hartbeespoort Dam.

After the success of the second water hyacinth biocontrol event earlier this year was short-lived due to the sudden and aggressive growth of the common salvinia (Salvinia minima), the tables have turned yet again as water hyacinth is recovering at a worrying pace. The Centre for Biological Control (CBC) at Rhodes University has successfully curbed the hyacinth invasion for the past years and is in the process of addressing the salvinia infestation, but funding has become a crisis.

“Unfortunately, funding which should have come into place on 1 April 2021 has not yet been awarded for the next cycle. We were granted a 6 month no-cost extension by the Department of Forestry, Fisheries and Environment (DFFE) which ended on 31 August 2021. Since then, we rely on pooling resources from other external funds, which support the salaries and running costs of the project until 31 October 2021, by which time we will be retrenching and closing down our facility. We need help to continue with the programme,” the CBC said. “We need all the financial help we can get to address the problem weeds on the dam.”

According to Professor Julie Coetzee, deputy director of the Centre for Biological Control at Rhodes University, the increase in water hyacinth growth at this time of year was not unexpected, as it is an incredibly aggressive invader, and typically regenerates every spring. “The new water hyacinth invasion is driven by seedlings and some plants that did not die last summer. Due to cold winter temperatures and how few plants remained after the summer, many of the biocontrol agents were lost over the winter, adding to the rapid growth rate of the weed,” she said. “Researchers from the Centre for Biological Control at Rhodes University continuously monitor the growth and spread of both species at the dam and use sophisticated satellite data to measure total cover. The cover, which is sitting at 14% for both species in early October, will continue to increase as the weather warms, but we have been releasing the planthopper, Megamelus scutellaris, since September. Efforts from the rearing stations around the dam are adding ten thousand per week, and we, at the CBC, are dispatching 15 000 every two weeks. We expect the insects to contribute to slowing the growth rate and prevent the excessive spread of water hyacinth, much as they did earlier this year.”

Work on the biological control agent for Salvinia minima is ongoing. A healthy population of the salvinia weevil, Cyrtobagous salviniae, arrived at the CBC quarantine facility at Rhodes University in August. The weevil was imported from Florida through the Florida Department of Agriculture and Consumer Services. “There, it is mass-reared and used exclusively to combat the noxious Salvinia minima or common salvinia in the southern states of the US. Currently, common salvinia is running rampant on Hartbeespoort Dam, and has spread to several other water bodies in the North West and Gauteng, and the newly imported weevil will be used to combat this invasion,” she said.

“She said if they have funding, CBC and partners around Hartbeespoort Dam will begin mass-rearing the weevil soon and intend to have the insect available for release later this year if given the go-ahead. The mass-rearing process involves monitoring temperature, water chemistry, plant health and insect populations to provide the optimal growth conditions for the weevil to flourish. Some time is needed to test, mass-rear and safely release the agent onto invaded sites, but the CBC is fully ready for the task ahead.”

The community and stakeholders are requested to assist with this very important programme. If stopped, Hartbeespoort Dam will soon be totally covered in the the weeds.

Visit the CBC’s crowdfunding page https://thundafund.com/project/6716626611215230 for all the information and to donate towards the programme.

For more information contact the CBC at cbcinfo@ru.ac.za or follow them on social media.

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