ENGLISH (see below for Afrikaans)
Water hyacinth is an invasive non-native weed from South America that has been on Hartbeespoort Dam since the mid-1960s. There has been a long history of control of this weed including herbicide application, mechanical/manual removal and biological control. Whilst all of these control interventions can be effective, biological control is considered the most sustainable and environmentally friendly.
A number of people have recently noticed a massive browning and die off of the weed on the dam which is unusual for this time of year when the plant usually thrives, forming thick extensive, green healthy mats across the water surface with beautiful purple flowers. This browning and die off of water hyacinth is not due to herbicide or chemical application, but rather the result of a buildup in populations of the biological control insects. These are the insects that people are noticing on the plants at the moment.
The two most noticeable insects are the Neochetina weevils, and the water hyacinth plant hopper, Megamelus, which come from South America too. These insects have been thoroughly studied in South Africa, and elsewhere, including the USA and Australia, over many years to make sure that they are safe (i.e. only feed on water hyacinth) and effective in controlling water hyacinth.
We believe that the lack of herbicide application over the last 2.5 years on the dam has allowed the biocontrol insects to build up their populations to a level where we are now noticing plant death. We at the CBC embarked on a mass release campaign over the last year, together with Pecanwood College and MCS, in consultation with #HartiesFoundation and other stakeholders around the dam, releasing tens of thousands of the plant hopper monthly. We continue to monitor these populations monthly.
There might be an algal bloom associated with the dieback of the plants as a result of an increase of light in the water column, unfortunately compounded by the high levels of nutrient pollution in the dam.
Frequently Asked Questions (FAQs)
What will the insects feed on when all the water hyacinth is gone?
A: the water hyacinth will never completely disappear from the dam, the insect populations will also decrease as the plants die, but should keep the small populations of the plants in check. These insects can only feed and reproduce on water hyacinth, no other plants will be affected.
How long will it take to clear the dam?
A: Biological control is a natural process and a long term but sustainable solution, the results on the dam are already significant, it has taken 2.5 years for the infestation to decrease to what it is today at 13%.
How does biological control fit in with mechanical control?
A: the biological control insects not only kill plants but they also stop the plants growing and spreading, allowing mechanical control to be more effective.
Are there any constraints?
A: the combination of cold winters and high nutrients could result in the plants recovering somewhat in Spring 2020. Further there will be germination from long lived seeds in the sediment, however every year that we do not get flowering our chances of success are higher. The CBC’s continual releases and monitoring will make sure that the insect populations build up faster than they would on their own.
What can I do?
A: Give feedback through this forum, but more importantly, please be patient with the natural process as it does take time.
AFRIKAANS
Waterhiasint is 'n indringende onkruid vanuit Suid-Amerika wat sedert die middel 1960's op Hartbeespoortdam voorkom. Daar is 'n lang geskiedenis van beheer van hierdie onkruid insluitend die toediening van onkruiddoders, meganiese / handmatige verwydering en biologiese beheer. Alhoewel al hierdie beheermetodes effektief kan wees, word biologiese beheer as die volhoubaarste en mees omgewingsvriendelik beskou.
‘n Hele aantal mense het onlangs opgemerk dat die onkruid op die dam gewelding verbruin en sterf. Dit is ongewoon vir waterhiasint vir hierdie tyd van die jaar, wanneer die plant gewoonlik floreer en dik, uitgebreide, gesonde groen matte oor die wateroppervlak vorm met mooi pers blomme. Hierdie verbruining en sterf van waterhiasint is nie te wyte aan onkruiddoder of chemise toediening nie, maar eerder as gevolg van ‘n opbou in die biologiese beheerinsekpopulasie. Dit is die insekte wat mense op die oomblik op die plante sien.
Die twee insekte wat die meeste opvallend is, is die Neochetina-kewer, en die waterhiasintplanthopper, Megamelus, wat ook vanaf Suid-Amerika afkomstig is. Hierdie insekte is vir baie jare deeglik in Suid-Afrika en elders, insluitend die VSA en Australië, bestudeer om seker te maak dat hulle veilig (d.w.s. slegs voed op waterhiasint) en effektief is om waterhiasint te beheer.
Ons glo dat die gebrek aan onkruiddodertoediening die afgelope 2,5 jaar op die dam die biologiese beheerinsektepopulasie in staat gestel het op te bou tot op 'n vlak waar ons nou plantdood opmerk. Ons by die CBC het die afgelope jaar in samewerking met Pecanwood College en MCS 'n veldtog vir massa-vrylating aangepak, in oorleg met #HartiesFoundation en ander belanghebbendes rondom die dam. In hierdie tydperk het ons tienduisende van die waterhiasintplanthopper maandeliks vrygestel. Ons hou aan om maandeliks die biologiese beheerinsekpopulasie te monitor.
Daar is moontlik 'n algebloei wat verband hou met die terugsterf van die plante en ‘n toename in lig in die waterkolom. Dit is ook vererger deur hoë vlakke van nutriëntbesoedeling in die dam.
Vrae wat gereeld gevra word
Waarop sal die insekte vreet as al die waterhiasinte weg is?
A: die waterhiasint sal nooit heeltemal uit die dam verdwyn nie; die insekpopulasie sal ook afneem namate die plante doodgaan, maar sal die klein waterhiasintpopulasie in toom hou. Hierdie insekte kan slegs op waterhiasint voed en voortplant; geen ander plante sal beïnvloed word nie.
Hoe lank sal dit neem om die dam skoon te maak?
A: Biologiese beheer is ‘n natuurlike proses en ‘n langtermyn, maar volhoubare oplossing. Die resultate op die dam is reeds beduidend; dit het 2.5 jaar geneem om die besmetting te verminder tot waar dit tans is op 13%.
Hoe pas biologiese beheer met meganesie beheer in?
A: die biologiese beheerinsekte maak nie net plante dood nie, maar hulle stop die groei en verspreiding van plante wat dus meganiese beheer meer effektief maak?
Is daar enige beperkinge?
A: ‘n kombinasie van koue winters en hoë nutriënte kan tot gevolg hê dat die plante in die lente van 2020 ietwat herstel. Daar sal verder ontkieming van langlewende sade, wat in die sediment is, wees. Alhoewel, elke jaar wat daar nie blomme is nie, vergroot ons kanse op sukses. Die CBC se voortdurende vrystellings en monitering sal sorg dat die insekpopulasies vinninger opbou as wat hulle op hul eie sou doen.
Wat kan ek doen?
A: Gee terugvoering via hierdie forum, maar meer belangrik, wees asseblief geduldig met die natuurlike proses, want dit neem tyd.