An invasive weed, disguised as a wolf in sheep’s clothing due to its bright purple flower, is spreading rapidly in the Noordhoek area and is toxic to horses.
The plant known as Patterson’s curse or salvation Jane (Echium plantagineum) contains pyrrolizidine alkaloids, a plant toxin, that can cause liver damage in livestock .
Noordhoek resident and former permaculturist, Etienne de la Harpe, is worried about the rapid spread of the weed in an area that is home to many horses.
He said the weed has spread to Silverglade, Sun Valley and as far as the False Bay Hospital in Fish Hoek.
He said that despite being toxic to horses, Patterson’s curse destroyed indigenous plants, such as fynbos, by poisoning the soil with a deadly alkaloid toxin preventing any further growth by other plants except itself.
A single plant can produce as many as 5 000 seeds which can amount to as many as 30 000 seeds per square metre.
It has a six-year incubation period and, if not pulled out, will spread in huge swathes. The seeds are primarily distributed by wind.
Dr Tine Schliewert, a senior lecturer in equine medicine and a specialist in equine internal medicine at the faculty of veterinary science at the University of Pretoria, said Patterson’s curse was one of many common liver-toxic plants consumed by horses.
She said the flowers and seeds were usually the most toxic components, followed by the leaves, stems, and finally the roots.
“The plants are most toxic when growing and heading toward bloom,” she said.
An adult horse needed to eat about 2% of its body weight of the toxic plant in order to develop liver failure. However, she said, the plants tended to be bitter, and horses would generally avoid them except in cases where the plant was incidentally baled in hay or chopped up in cubes.
Progression in affected horses depended on the duration of exposure and the amount of ingested toxin but was usually slow and continuous.
“Therapy is symptomatic, there is no cure; we can only slow down progress and help the horses feel better,” she said.
Dr Schliewert said that when the plants were consumed, the liver metabolised the pyrrolizidine alkaloids, killing liver cells and causing widespread scarring of the liver.
The toxin caused ongoing damage until the horse exhibited acute onset neurologic signs such as weight loss, reduced appetite, jaundice, and photosensitisation.
“Once you identify a horse with clinical signs, however, it might be too late to investigate the hay or forage source for poisonous plants. If the source of the toxin is forage fed to all horses in a herd, multiple horses might be affected,” she said.
The Echo tried to speak to horse owners in the area, but they were reluctant to comment.
Some said they knew the plant was poisonous while others said they were not worried about it as their horses did not eat it.
Noordhoek resident Kathy Fish also expressed her concern about the spread of Patterson’s curse.
She runs a community project, On the Verge, once a week on a Wednesday to clean the verges in the area and plant trees. She said they pulled Patterson’s curse out of the ground whenever they saw it, but it was difficult as large patches of it grew in privately owned horse paddocks across Noordhoek.
“People should be educated about this plant. Not many people are aware that it is an invasive weed, and because of its beautiful purple flower they think it is harmless,” she said.
According to Invasive Species South Africa, Patterson’s curse is listed as a category 1 invader plant, according to the Conservation of Agriculture Resources Act of 1983, meaning plants must be removed and destroyed immediately and trading of the plant is prohibited.
Ward councillor and mayoral committee member for transport and urban development, Felicity Purchase, said controlling the plant is very difficult as it can flower and seed numerous times during October to April.
She said the weed is spread across the Western Cape and
studies have been undertaken to find environmentally friendlier ways to manage this plant including biological control methods.
Currently, she said, the most effective way to control the weed is a combination of
chemical and mechanical methods which are very expensive and not
always possible to implement.