Shirley Tebbutt is making every effort to remove the water hyacinth plant that has completely covered the Delta Park dam as a result of a six-week sewer leak.
Recently, members from the South African Institute for Aquatic Biodiversity (SAIAB) and the Centre for Biological Control (CBC), Professor Julie Coetzee, Dr. Kelby English, Kim Weaver, and Nicolas Salinas visited and released megamelus scutellaris, the hyacinth hopper into the dam.
The hoppers are expected to eat and kill the plants. They feed on the plants, by inserting a straw-like mouthpart that allows them to suck up the plant’s sap. In so doing, they also introduce plant diseases caused by fungi and bacteria. The plant gradually starts to die and stops producing flowers and daughter plants.
About 25 000 hoppers were recently released into the dam. Coetzee explained that the biological control takes time. “It is not a quick fix, but if we get enough bugs onto the system, particularly in spring time when the plants start to regrow, we could see a significant reduction within a year.”
She added that it’s important to know that biological control does not aim to eradicate the invasive weed but to get the population to an acceptable level of control. If they can reduce the cover by 85-90%, they will consider this an excellent result.
“We will continue to release the hoppers as long as we can keep supplying them from our mass-rearing facility at Rhodes University in Makhanda. We would ideally like to set up a rearing station at Delta Park that could continually supply the dam with bugs, but there are all sorts of logistical constraints to that, the biggest being theft.”
Tebbutt said that the hyacinth does not root in the sediment as they are floating. She added that removing water hyacinth has become too big and complicated for her and her team. “This now is a job that is way too big. Unless someone gives us R20 000 or R30 000 I will have to find people who know how to swim and know about these plants. This is a disaster.”
Manual removal can help to keep key areas of the dam clear but takes a lot of effort to do so. Chemical herbicides are also available for water hyacinth control, their application requires a certified pest control officer to apply the herbicide.
“Herbicides result in quick death of the plants, but they also kill the bugs, and any plants left behind results in a resurgence of the weed.”
Coetzee added the planthoppers will kill the water hyacinth in high numbers if they are released frequently at the Delta Park Dam.
For the Delta Park newsletter contact Shirley Tebbutt: firstname.lastname@example.org
Coetzee was asked in a Q&A format to explain more about water hyacinth plants and plant hoppers.
More on the water hyacinth plant:
Q: Where are Hyacinths originally found in nature?
They are from the Amazon Basin in South America.
Q What other damage do they do in the water?
The mats of water hyacinth block out the sunlight, which prevents submerged plants and phytoplankton from photosynthesising. Photosynthesis produces oxygen, so if this is prevented, there is no oxygen left in the water, and most of the organisms living in the waterbody die. So, fish, insects, crabs, snails, etc. that need to take up oxygen from the water column are negatively affected.
Q Is the plant a problem in other places or countries?
Water hyacinth is the world’s worst aquatic weed, it is invasive on every continent except Antarctica. It is particularly problematic in the tropical and subtropical parts of the world.
Q How does it spread and how quickly does it grow?
Water hyacinth spreads by people moving it from system to system. For example, many fishermen believe that it provides good protection for baby fish, so they move it around to fishing spots. It has a very beautiful flower, so water plant enthusiasts share it around, although hopefully now people know how bad it is. Water hyacinth can double in biomass every 10-14 days under ideal conditions, so when it is hot and there are lots of nutrients in the water.
Q What can be done to prevent these plants in other dams?
Firstly, awareness is key, water hyacinth must not be moved around – it is illegal to do so under the National Environmental Management: Biodiversity Act (NEMBA). Early detection is very important – if the plant is noticed in a system, it must be reported to either the CBC – email@example.com or South African National Biodiversity Institute (SANBI) – firstname.lastname@example.org
The plants also thrive in nutrient-rich water, so we need to prevent sewage spills into our water bodies as this provides nitrates and phosphates that the plants thrive on.
More information on hoppers/ bugs
Q What are these hoppers?
The hoppers are biological control agents, natural enemies of water hyacinth. They are sap-sucking bugs in the family delphacidae
Q Are they not a threat to other species in the dam?
These bugs have been tested under quarantine conditions to ensure that they are host-specific, which means they can only feed on water hyacinths, and can only reproduce on water hyacinths. No other species in South Africa are at threat from them.
Q How quickly do they reproduce?
Their life cycle is approximately three weeks, which is quick for a biocontrol agent.
Q Where are they coming from?
The bugs originate from South America, where water hyacinth is indigenous. Our hoppers in particular came from Argentina.
Q Do people need to be concerned about the hoppers?
Not at all! They pose no threat to the environment, they cannot harm people or any other organism, we need to embrace them and appreciate the work they do for us, at no cost.
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