Effective prevention and treatment of inkberry and tulip poisoning

Estimated reading time: 5 minutes

• Poisonous plants like inkberries (Cestrum species) and yellow tulips (Moraea pallida) pose serious risks to livestock health, leading to fatalities and economic losses.
• Inkberries are invasive in South Africa, with Cestrum laevigatum affecting coastal areas and Cestrum parqui spreading inland, and can cause Chase Valley disease in animals.
• The ARC-PHP has launched a biological control programme to manage Cestrum spp., testing potential insect or pathogen agents from South America as a cost-effective, sustainable solution.
• Yellow tulips contain cardiac glycosides that can cause heart issues in livestock, with tachycardia and arrhythmias, and although activated charcoal can treat poisoning, it must be administered promptly.
• Preventive strategies include herding, fencing, and plant removal, but while feed aversion techniques have shown limited success, activated charcoal has helped recovery if used early.

Poisonous plants are known for their toxic chemical compounds and can be harmful and even deadly to livestock that ingest them. Inkberries (Cestrum species) and certain tulip species, particularly yellow tulips (Moraea pallida), are among these dangerous plants. They not only cause animal deaths but also lead to significant economic losses due to a decline in body condition and reduced animal health and productivity.

Significant risk to cattle

Dr David Simelane, a specialist researcher at the Agricultural Research Council (ARC), explains that poisonous inkberries are native to the tropical Americas and are invaders in subtropical regions worldwide, including South Africa. The four exotic Cestrum species are Cestrum laevigatum, Cestrum parqui, Cestrum aurantiacum, and Cestrum elegans. Of these, C. laevigatum and C. parqui are invasive, while C. aurantiacum and C. elegans are still limited to a few areas.

C. laevigatum is the most invasive in South Africa, especially affecting the coastal regions of KwaZulu-Natal and the Eastern Cape. Conversely, C. parqui is widespread inland, invading grasslands and suburban areas across Gauteng, North West, Limpopo, Free State, Mpumalanga, and Northern Cape. All Cestrum species are toxic to animals, including cattle, and can cause Chase Valley disease, named after the first outbreak recorded in Chase Valley near Pietermaritzburg in KwaZulu-Natal.

Read more about invasive alien plants and their impact on wetlands.

Biological control programme

Dr Simelane explains that traditional methods for controlling Cestrum spp., such as mechanical and chemical approaches, are often challenging, costly, and time-consuming. Physical removal of the plants is difficult, and chemical control requires repeated treatment, which can also affect non-target species. In response to the rapid spread of Cestrum spp. in agricultural and conservation areas, the ARC Plant Health and Protection Unit (ARC-PHP) has launched a biological control programme. This programme now focusses on biological control, which is regarded as a more cost-effective, environmentally friendly, and sustainable method for managing these plants in South Africa.

Classical biological control involves selecting and introducing insects or pathogens from the plant’s native region. Over a dozen potential control agents have been identified in South America, with four currently undergoing testing in ARC-PHP’s quarantine facility. These tests aim to determine whether the agents are suitable for release. Dr Simelane says once the risk level of a potential agent is assessed, permission will be sought from the Department of Agriculture to release it into the wild. Researchers at ARC-PHP have completed testing on one promising biological control agent and, if successful, it is set for release within the next year.

Read more about the ins and outs of invasive plant management.

Findings on the yellow tulip

A 2019 study published in the Journal of Immunological Methods investigated raising antibodies in rabbits against epoxyscillirosidine, a toxin in yellow tulip. This research highlights the serious economic impact of yellow tulip poisoning, causing significant livestock fatalities in the country. Cardiac glycoside poisoning accounts for a substantial percentage of livestock deaths, estimated at around 33% in cattle and 10% in small stock. Poisoned animals present with tachycardia and arrhythmias, and treatment is often unsuccessful. However, activated charcoal can be an effective treatment but it must be administered soon after ingestion and, in addition to being expensive, can cause stress to animals.

Preventive measures

The research paper suggests prevention of yellow tulip poisoning by herding animals, fencing off infested areas, or physically removing the plants. While chemical control with herbicides is sometimes used, it is costly and has ecological impacts. Vaccination or immunotherapy could be explored as alternative strategies. Successful vaccination against small-molecule plant toxins requires conjugating toxins to larger proteins to trigger an immune response.

In the paper, Prof Christo Botha, a veterinary toxicologist from the Department of Paraclinical Sciences at the University of Pretoria’s Faculty of Veterinary Science, and his colleagues investigated vaccine development. Although antibodies were raised in animals, in vitro testing failed to prove its effectiveness. Prof Botha mentions that Snyman and colleagues at the ARC-Onderstepoort Veterinary Institute have studied feed aversion techniques, published in the Onderstepoort Journal of Veterinary Research (2003), and the use of activated charcoal for treatment, published in the Journal of the South African Veterinary Association (2009).

Read more about the principles of a vaccination programme for cattle.

While feed aversion reduced severe poisoning, mild poisoning rates were similar among treated and untreated cattle. However, activated charcoal aided recovery when administered early, though severe cases may still result in mortality. – Christal-Lize Muller, Plaas Media