A cacti epidemic

Dangerous plant infestation in Namibia
Saskia Damaschke
Saskia Damaschke
Cacti are not a rare sight in Namibia. For some they are a beautiful ornamental plant, but for Gunhilde Voigts, the plants are a dangerous invader species.
Having founded Cactus Clean-Up, she is committed to removing these plants that place indigenous vegetation in danger.
The idea that a cactus is dangerous is not far-fetched: after all, they have spikes that can hurt you. Voigts sees other dangers and wants to ensure that Windhoek and Namibia in general are freed from these “invasive” plants.
“If someone throws away a plastic bottle and no one picks it up, in a year it will still be there. But if a cactus or other harmful plant grows there and no one removes it, then at least ten new plants will grow there in the next year,” she explains.
What are invasive species?
While flowering vegetation is beautiful, there are plants that have no use and are harmful. For example, there is fountain grass - Pennisetum Setaceum - which many people plant in their gardens. The seeds are scattered and the grass grows quickly, leaving no room for local vegetation.
The problem with this is that it cannot be eaten by herbivorous animals and it is taking over Namibian grasslands. As a result, it harms the local vegetation and takes away space for food for wild animals.
Other shrubs grow so fast and dense that the animals can no longer get through. Voigts cites the Waterberg Plateau as an example where the rhinos can no longer make their way through the thickets.
It is important to carefully remove such plants. “Unfortunately, these harmful, invasive plants are not easy to exterminate,” Voigts says. “If you don’t remove them all, then the entire success of a removal operation is at risk. What we don't remove now, will increase next year.
Operation Cactus Clean-Up was launched in 2015. Voigts and her family are members of the Botanical Society and have been involved in actions to remove invasive plants from the botanical garden on several occasions.
“You realise that these efforts are completely in vain if the entire Namibian vegetation is replaced by ‘invaders’, which include cacti. These actually come from South America, but in time have spread all over the world.
“In Windhoek, there are now more than 23 different types of cacti. They are hardy. With their shallow root system, they use rainwater first and only leave a little behind for other plants. Cacti can store water and survive dry seasons, while others need to grow again from seeds or rootstocks every season.
“So, compared to other plants, cacti grow and spread quickly. The damage such a cactus infestation can cause is often underestimated. Sometimes farms were so infested with cacti that removing them can cost more than the farm itself.”
Get involved
A large number of cacti can be seen in Windhoek. In some spots there has been a decline, mostly thanks to Voigts and her team.
“If we want to prevent a complete collapse of our own vegetation, we need to tackle this problem together. The quickest and most effective way to do this is to get physically active. All residents should take up their rakes and boxes and pull out each individual cactus wherever it is sighted. The uprooted plant must be buried under several meters of rubble on a landfill site to no longer reproduce,” she said.
“If someone prefers to pay workers to do the work, experienced job-seeking ‘cactus fighters’ are available. We pay them N$150 for a day's work. We provide them with tools, sandwiches, coffee and water.”
However, this is not a once-off job. “Aftercare is required to prevent remaining seeds from germinating and new cacti from spreading.”
In addition to burying the cacti under rubble, Voigts also burns some plants at home. “I always have to let the neighbours know that the house is not on fire!” she says with a smile.
Cacti can also be destroyed by mealybugs. Voigts points to cacti on which cochineal insects are attached. In some places, the cacti have died but in others they continue to grow happily.
Thus the most effective method remains the careful manual removal and subsequent burning or burial of the cacti.
At the moment, however, it is not the cactus that has caught Voigts’ attention, but rather the datura (belonging to the nightshade family) which is spreading like wildfire in Windhoek. It is poisonous and also belongs to the group of harmful invasive plants.
For more information, visit https://www.cactusclean-up.com/