“Following the successful reduction of water hyacinth at the beginning of this year, common salvinia cover increased steadily from about 10 ha to 440 ha, or 24%,” said Dr Kelby English of Rhodes University’s Centre for Biological Control (CBC).
“Cover appears to have stabilised in recent weeks and fluctuates between about 20 and 30% depending on the wind, cover continues to be monitored by the CBC.”
She said recent field surveys indicate that water hyacinth has started to grow vegetatively. Hyacinth currently covers 0.8% of the dam (14 ha).
“As seen in previous spring seasons, water hyacinth growth will soon suppress the common salvinia and outcompete it. The water hyacinth biocontrol programme is currently progressing according to plan.”
CBC will release the “hyacinth bugs” as soon as hyacinth reappears.
“Although the biocontrol agents reduce water hyacinth flowering and, therefore, seed output, there is still an extensive seed bank in deeper sediment. The El Niño climate pattern brings uncertainty regarding rainfall and dam water levels, which influences seed germination and growth,” she said.
According to John Wesson of WESSA, hyacinth should be rearing its ugly head by next week if the current hot weather conditions continue.
“Hyacinth germinates at approximately 20 degrees, and seeds will germinate quickly in the shallow water near the shore,” he said.
