Green cestrum (syn. Chilean cestrum, Green poison berry) is a woody shrub introduced from South America as a garden ornamental. Unfortunately, it has escaped and become established as a significant weed in Eastern Australia.
Cestrum favours warm-temperate climates and good soils, particularly alluvial soils on which it thrives. On good soils, it is capable of growing to 3-4 metres high.
In NSW, the main distribution is the coast, Sydney Basin and Hunter Valley. However, green cestrum could potentially be encountered anywhere in areas where it has been planted in gardens and subsequently escaped. The weed is also well established in south-eastern Queensland. The plant is typically found in vacant allotments, rubbish dumps, around farm buildings & on river or creek banks. Because of the capacity of birds to spread the weed in their droppings, green cestrum could potentially be found anywhere within a flight radius of gardens or other areas containing this plant. Green cestrum is also spread downstream through the water transport of root segments during floods.
Flowers: Very characteristic — greenish-yellow to yellow, tubular shaped flowers, 2-2.5cms long, ending in 5 star shaped, yellow lobes (Everist, p625). Flowers mainly spring-autumn.
Leaves: Dark green, 5-10cms long, 1-2.5 cms wide, unpleasant odour when crushed (Everist, p625).
Stems: More mature stems are woody, grey and ‘warty’ in appearance.
Roots: Yellow. Unpleasant odour when broken. The plant will produce new plants from suckers, either from intact roots or from root pieces left behind after attempted removal.
Fruit: A purplish to black, ovoid berry develops from the flowers. It is about 1cm long, containing 1 or 2 seeds in a dark purple pulp (Parsons & Cuthbertson, p593).
The texts report toxicity mainly in cattle and poultry, rarely in pigs and the plant is also known to be toxic to sheep, horses and humans. I would add goats to the list, since there have been several anecdotal reports of goats in the Sydney Basin dying after eating green cestrum. However, I know of at least 1 case where several feral goats used for scrub control became sick but survived after browsing green cestrum.
All parts of the plant are reported to be toxic, with some sources suggesting that the berries are the most toxic part of the plant (and a possible risk for young children). Toxic principles specified are a saponin (suggested to be parquine by Parsons and Cuthbertson) and solasonine (McBarron, pp66 and 92).
The issue of toxicity to birds is interesting. Reports of toxicity to poultry relate mainly to consumption of leaves. There must be at least one bird species which is resistant to the known toxicity of green cestrum berries, due to the well known dispersal of seed in bird droppings, as demonstrated by seedlings frequently coming up under tree branches or fences. I’m not aware which birds are responsible, but the Currawong (with its berry eating habits) would have to be a prime suspect.
In my view, green cestrum is the largest single cause of sudden death in cattle in the Sydney Basin. Typically, the picture is of several cattle found dead for no apparent reason, having been seen to be healthy 24 hours previously. Cattle are rarely vaccinated, and blackleg is a differential diagnosis. I normally only see carcasses, but owners who have seen their cattle die often report that ‘they die in agony’. In my experience, where cattle have been treated by practitioners, treatment has invariably been unsuccessful. The primary lesion of acute hepatic necrosis appears to be too severe for cattle to be able to survive.
Typical symptoms are described as fever, loss of appetite intense abdominal pain and blood-stained scours are reported (Everist, p625). Nervous symptoms and aggression are sometimes reported, attributable to a hepatic encephalopathy rather than direct toxic effect on the brain.
The pathology of green cestrum poisoning is discussed by McLennan & Kelly. They describe a swollen liver, with accentuation of the acinar pattern. They also describe haemorrhage in the abdomen, heart and gall bladder. I have not seen as many cases as they describe (mine are usually too far gone for gross pathology to be of value), but in the fresher cases, liver pathology has been prominent, with occasional blood in the lumen of the small intestine, but without the other haemorrhages described. The consistent and primary lesion is hepatic necrosis — green cestrum is one of the most severe causes of this condition in cattle. Histopathology reveals a periacinar necrosis which is often extremely severe and lethal.
Prior to performing an autopsy, where green cestrum is suspected, I will usually do a paddock walk. Evidence of heavy browsing of green cestrum plants is sufficient for a field diagnosis in my view. The owners usually have no idea that the plant is toxic, and stories of cattle coexisting with the plant for months and then suddenly deciding to eat it are common. While dry conditions make this more likely, they are not the only reason why cattle will eat green cestrum. In fact, I have no idea why they touch it and then, having tasted the plant, then continue to browse until they receive a toxic dose. I can only suggest, given the nasty smell of the plant which you would think was accompanied by a nasty taste, that the plant is palatable at certain times to cattle, and possibly even addictive.
As with other plant poisonings, green cestrum may be more palatable when it is wilting after removal or spraying. There was a sad case on one Hawkesbury River farm where a farmer lost 5 valuable stud bulls after they had eaten wilting green cestrum which the farmer had dug out but left in the paddock. The bulls had apparently coexisted in the same paddock with the green cestrum without touching it for months.
Green cestrum poisoning in cattle is best avoided in our experience through the education of cattle owners that green cestrum must be removed from any paddocks where they wish to run stock. A poster has recently been produced for field day displays. A 1 page handout (see Appendix 1) was produced for a field day by veterinary intern Xanya Hill in Nov. 2004, and provides a useful, user-friendly one page summary on the problem of Green Cestrum toxicity in cattle. Control methods have not been specified, due to problems with unqualified people giving pesticide advice.
Green cestrum control can be placed into 3 categories:
1. Mechanical removal. Not practical for larger specimens, which have a tenacious root system.
2. Cut stump technique (painting a freshly cut stump with a registered herbicide)
3. Weed sprays — see DPI or local council weeds officer for current advice.
Regrowth is a potential problem with all methods, and follow up control is usually necessary.
In summary, green cestrum is a major cause of sudden death in cattle in the Sydney Basin. Cattle should not be allowed to graze in any areas where this weed is found. The main problem is lack of owner recognition of this highly toxic weed.
Everist, S.L. (1981) — In Poisonous Plants of Australia, Rev Ed.,Angus & Robertson, Sydney, p625
Hurst, E. (1942) — The Poison Plants of NSW, NSW Department of Agriculture, Sydney
McBarron, E. (1976) — Medical and Veterinary Aspects of Plant Poisons in NSW, NSW Department of Agriculture, Sydney
McLennan, M. & Kelly, W. (1984) — Cestrum parqui (green cestrum) poisoning in cattle — Aust.Vet.J. 61: 289-291 Parsons, W. & Cuthbertson, E. (1992) — Noxious Weeds of Australia, Inkata Press, Melbourne