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 Post subject: Invasive alien: Water hyacinth
Unread postPosted: Mon Nov 28, 2005 6:41 pm 
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Does anybody know why these buoys are across the Makhadzi where it enters Engelhard Dam?

October 2005:
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Unread postPosted: Tue Nov 29, 2005 6:20 am 
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DB, I might be wrong but I think the pic illustrates it very nicely. It seems to be blocking up all those green water plant crap. I might be totally wrong but I really think that it prevents this and other alien plant species to spread down the river. Probably a working for water project.

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Unread postPosted: Thu Dec 01, 2005 6:34 pm 
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That was my guess too WTM.

The plant is known as Water Hyacinth. It is an invasive alien species that has been targeted for removal from all bodies of water in SA, if not controlled it would easily cover the entire dam or river, whilst it actually cleans the water, it blocks certain waterways and also prevents birds that rely on hunting for fish, such as Fish Eagles and Kingfishers from catching their prey.

It multiplies by spreading its floating bulbs, and does so rapidly. I think that by blocking it off, they can prevent much of it from travelling down river and they can clear it out where it gets caught by the nets.

This is still just a guess.

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Unread postPosted: Thu Dec 01, 2005 7:48 pm 
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Could well be a controll net , I like wtm's description of the plant though :P

They have also intoduced biological control in the form of a weavel that eats the plant in no time at all , but the only thing is that the weavel is dormant through winter(or is it summer) , and the plant builds up numbers during that time .


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Unread postPosted: Thu Dec 01, 2005 8:05 pm 
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Is this the same alien plant that covered Sunset Dam, I thought it was called water lettuce :?
The weavil was used there and it seems to have been so successful that they have taken all the explanatory signs down 8) and the dam has been clear for over a year now.


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Unread postPosted: Thu Dec 01, 2005 8:36 pm 
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Freda wrote:
Is this the same alien plant that covered Sunset Dam, I thought it was called water lettuce :?
The weavil was used there and it seems to have been so successful that they have taken all the explanatory signs down 8) and the dam has been clear for over a year now.


Yeah, it sure is

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Unread postPosted: Thu Dec 01, 2005 10:34 pm 
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Was it gone in winter also ? normally covers it during winter when the weavils are not about , that would be great if they actually totaly removed it .


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Unread postPosted: Fri Dec 02, 2005 9:32 am 
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Sunset Dam was still clear, as far as I can remember in June this year.

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Unread postPosted: Fri Dec 02, 2005 10:08 am 
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The seven species of water hyacinths comprise the genus Eichhornia of free-floating perennial aquatic plants native to tropical South America. With broad, thick and glossy ovate leaves, water hyacinths may rise some 1 metre in height. The leaves are 10-20 cm across, supported above the water surface by long, spongy and bulbous stalks. The feathery, freely hanging roots are purplish black. An erect stalk supports a single spike of 8-15 conspicuously attractive flowers, mostly lavender to pinkish in colour with six petals. When not in bloom, water hyacinth may be mistaken for frog's-bit (Limnobium spongia).

One of the fastest growing plants known, water hyacinth reproduces primarily by way of runners or stolons, eventually forming daughter plants. They may also reproduce via seeds. The common water hyacinth (Eichhornia crassipes) is a vigorous grower known to double its population in two weeks.

Water Hyacinths have been widely introduced throughout North America, Asia, Australia and Africa. In many areas they, particularly E. crassipes, are important and pernicious invasive species. First introduced to North America in 1884, an estimated 50 kilograms per square metre of hyacinth once choked Florida's waterways, although the problem there has since been mitigated. When not controlled, water hyacinth will cover lakes and ponds entirely; this dramatically impacts water flow, blocks sunlight from reaching native aquatic plants, and starves the water of oxygen.

Directly blamed for starving subsistence farmers in Papua New Guinea and Australia, water hyacinth remains a major problem where effective control programmes are not in place. In some areas, the plants are however more valued, being harvested for cattle food. The plants also create a prime habitat for mosquitos, the classic vectors of disease, and a species of snail known to host a parasitic flatworm which causes schistosomiasis (snail fever).

As chemical and mechanical removal is often too expensive and ineffective, researchers have turned to biological control agents to deal with water hyacinth. The effort began in the 1970s when USDA resarchers released three species of weevil known to feed on water hyacinth into the United States, Neochetina bruchi, N. eichhorniae, and the water hyacinth borer Sameodes albiguttalis. Although meeting with limited success, the weevils have since been released in more than 20 other countries.

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Unread postPosted: Fri Dec 02, 2005 10:43 am 
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The control of water hyacinth is a very delicate operation, as mentioned it does clean/filter the water so total removal of it with no precautionary steps can sometimes upset the balance. Hartebeestpoort dam is a good example where they introduced the weavel and eventually cleared the whole dam, unfortunatley the weavel cleared almost all vegetation and now the dam has a new problem of the water becoming stagnant and dirty. Sunset dam is rather small and I would think easier to control but Lower Sabie is another problem all together. From what I understand the best natural control is the Hippo. So maybe the bouys keep it in check and the Hippos do their part. Total eradication by 3rd party solution like spray or weavel might have adverse effect. Kruger has a department that deals with alien invasion, maybe they can give us a clearer picture.


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Unread postPosted: Fri Dec 02, 2005 10:24 pm 
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Most 'natural' solutions don't seem to be all that natural when you weigh things up. The problem with introducing a second foreign 'agent' to deal with the first is that you may have a trickier problem getting rid of number two.

The smaller the entity the harder it is to monitor its effect. If the weevil (in this case) causes destruction of other flora then the cost may be too high. I bet there is a South American something or other that preys on the weevils - so maybe that will be needed later (and after that there will something that preys on that and so on...).

I'm sure the powers that be have thought long and hard about introducing weevils and such but the idea of stopping its spread by 'damming' seems a very logical first choice.

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Unread postPosted: Fri Dec 02, 2005 10:52 pm 
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From what I have heard the weavil only eats the invader plant here in south africa .
Extensive studies are carried out before any biological agent is introduced .


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Unread postPosted: Sat Dec 03, 2005 9:11 pm 
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Snoobab wrote:
Kruger has a department that deals with alien invasion, maybe they can give us a clearer picture.


Does anyone know who we can contact in this department as I have been trying to get a response to a very serious invasion of Water Hyacinth in the Crocodile River in front of Ngwenya Lodge and towards the Hippo Pools area. It has completely blocked large tracts of the river where previousy large herds of Hippos resided.

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 Post subject: Response from Alien Biota Control
Unread postPosted: Tue Dec 06, 2005 2:02 pm 
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Dear Forumites
I have seen your questions and I managed to get a response from Llewellyn Foxcroft from the department.
I trust this helps.

Kind regards
KNP Spokesman


Dear All,

I noted the discussion regarding the cable and alien plants at Engelhard dam with much interest- certainly the awareness of alien invasions is vastly improved on a few years ago. I thought I could provide some details on the situation..

The plant that you see on Engelhard dam is indeed water hyacinth (Eichhornia crassipes), of South American origin. It is now one of Africa's most serious plant invaders. Although hyacinth is only found from Engelhard dam downstream, there are invasions outside the KNP that we are aware of, and are under the control of the Limpopo province working for water programme. The plant that was very visible on Sunset dam was water lettuce (Pistia stratiotes). It still occurs on the Sabie river. It was controlled, or rather, is still under control by the snout weevil, Neohydronomus affinis. I will mention a bit more on biocontrol shortly.

The cable on the dam or confluence of the Makhadizi spruit is part of a long-term management and research programme that we are coordinating. Unfortunately hyacinth must be one of the most difficult aquatic invasive alien plants to control. Although aerial applications (from helicopter usually) are effective, i.e. the herbicides are specific and do kill the hyacinth, it is expensive and needs to be done over a long period. It would be impossible to eradicate the plants from the system. However, although biocontrol agents are very effective, they are not providing the level of control that we had hoped for. There are a number of reasons and even guesses for this. In order to develop a long-term monitoring and research project to look at the potential for the biocontrol to manage the hyacinth, we divided the dam surface are into two areas for management / research purposes. All the plants that are found behind the cable (the Makhadzi spruit side) will be left entirely under the control of the biocontrol agents. The rest of the dam's surface can be managed by alternative means, using herbicides from either a helicopter or from the shore. We have also designated the biocontrol part of the dam as a biocontrol reserve under the Conservation of Agricultural resources Act, in order to ensure that we can maintain it as a biocontrol reserve. As the insect numbers build up, they can naturally move onto plants in the other area as they wish, thus forming an integrated control plan (biocontrol and herbicide control). About every 4-6 weeks researchers from WITS University go to the dam and collect data on various aspects (such as insect types present, size of leaves etc). The project is still busy, so we haven't received any finalized results yet.

On the issue of biocontrol I can briefly mention that biological control has been practiced world wide for 130 years, with approximately 274 agents having been released on various problem plants. In South Africa, 73 agents have been released on 29 weed species, and 19 agents have been released in and around the KNP. The first question asked is whether biocontrol agents will spread onto other indigenous plants. The answer is, NO, these agents are brought into the country under strict quarantine facilities and are extensively tested to ensure that even in the event that there are no host food plants left, they will not disperse onto indigenous plants. This testing includes all plants related to the alien host plant and may take up to 5 years to complete.

Yours sincerely
Llewellyn Foxcroft
Programme Manager: Invasion ecology and river research
Savanna Ecological Research Unit, Skukuza


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 Post subject: Hyacinth
Unread postPosted: Sun Mar 30, 2008 2:12 pm 
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There was a huge problem with Hyacinth at Sunset dam some years ago. IIRC the dam was completely overrun with it in Aug 2000.

Can someone tell me if the proble has been resolved? The recent pictures I've seen on the forum of Sunset dam look great but would apreciate of someone can confirm this for me.

Are there any other dams where this is a problem?

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