Like many of our noxious weeds, green cestrum (Cestrum parqui) was introduced into Australia as a garden plant. Easy to grow, its attractive, yellow flowers guaranteed widespread plantings in gardens everywhere (photo left – good example).
Birds and river systems have done the rest, spreading the plant’s fruit into rural areas in many parts of E. Australia. Birds spread green cestrum fruit from garden situations to neighbouring areas. Usually, the birds head for the cool shade of trees along waterways. The new plants flourish in these well-watered areas.
How to identify green cestrum
Green cestrum flowers are yellow and trumpet-shaped. The dark green leaves are smooth and shiny. This photograph also shows the berries – some green and some ripe, black ones. Cestrum grows to a height of around 3 metres. Apart from the distinctive, yellow, trumpet-shaped flowers, there are two other important identification procedures:
- The stems/branches are very brittle. They snap off easily.
- Crush a leaf between your fingers. The smell is very unpleasant! (Wash your hands afterwards!)
Green cestrum sheds some of its leaves through the winter, and new growth kicks in during spring. Green cestrum officially flowers late spring to late summer. But, in north west NSW, green cestrum seems to flowers all year except mid-winter! Green cestrum can cause some human health problems e.g. contact with crushed leaves and green berries in particular has been reported as causing elevated temperatures and hallucinations.
On a much more serious note, green cestrum can be extremely toxic to animals including sheep, horses, pigs, poultry but ESPECIALLY CATTLE!
According to “Noxious Plants of Australia” by Parsons & Cuthbertson (Inkata Press) it doesn’t take much plant material to affect animals, who “become feverish with poor appetites and increased thirst, are excited and sometimes scour before developing a general paralysis. Death usually occurs within hours of the first signs of symptoms so animals are often found dead without any symptoms being seen. Post-mortem examination shows general haemorrhaging throughout the body tissues, a large amount of blood in the bowel and severe gastroenteritis.”
Stock owners should NEVER take the plant for granted: Green cestrum is a mysterious plant. Animals can graze in amongst it for months without any problems. Then, “out of the blue”, a change of weather conditions (especially light rain after an extended dry spell) or some other climatic phenomena triggers a change in the chemistry of the plant which in turn makes the plant attractive to stock – especially hungry stock. The main danger period for animals is when the plants have been broken off, chemically treated or drought affected. As the plant material dries out, it can become more attractive to animals. Any part of the plant can be toxic. Another danger period is when stock, particularly cattle, are put into a new paddock. In these situations, stressed and disorientated animals will often try a variety of plants that they would not normally eat.
1. Manual control is an option for small patches. Physical removal of all plant material is very difficult because of the complex root system but the plant will eventually give up if you keep at it! Never leave any plant material where it can be eaten by stock. Drying plant material is at its most dangerous!
2. They are a number of herbicides registered for treatment of green cestrum. Again, a word of warning! Animals may be tempted to eat the plant material as it is drying out. Keep stock away until well after the leaves and other soft parts of the plant have decomposed. According to NSW DPI’s excellent booklet “Noxious and Environmental Weed Control Handbook 6th Edition”, herbicide treatments include:
|Metsulfuron-methyl 600g/L PLUS Triclopyr 300 g/L + picloram + aminopyralid 8 g/L Grazon Extra®||500 ml per 100 L water||Apply from late spring to early autumn when bushes are active. Regrowth and seedlings must be resprayed when 1 m high|
|Triclopyr +picloram 300 g/L + 100 g/L eg Grazon DS®|
|Triclopyr + picloram 240 g/L + 120 g/L eg Access®||1.0 L per 60 L diesel||Basal bark application|
|2,4 -D + picloram 300 g/L + 75 g/L eg Tordon 75D®||650 ml per 100 L water||Actively-growing bushes in full leaf|
|Amitrole + ammonium thiocyanate 250 g/L + 220 g/L eg Amitrole T®||1.1 L per 100 L water||Handgun application only. Aquatic areas: drains, channels, streams, lakes and dams. Active growth, before flowering|
|Triclopyr 600 g/L eg Garlon®||170 ml per 100 L water||Re-treat regrowth next season|
|Triclopyr 600 g/L eg Garlon®||1.0 L per 30 L diesel||DO NOT over treat as excessive run-off might affect adjacent trees and shrubs through root absorption. Please refer to Permit PER11427 for full details. NSW only.|
|Glyphosate 360 g/L (various trade names)If using heavier strength glyphosate reduce rates accordingly||1 part glyphosate to 1.5 parts water||Cut, scrape and paint. Full details see Permit PER9907|
|spot spray 100 mL per 10 L water||Spot spray. Full details see Permit PER9907|
|Picloram 45 g/kg Vigilant®||Undiluted||Cut stump/stem injection application. Apply a 3–5 mm layer of gel for stems less than 20 mm. Apply 5 mm layer on stems above 20 mm (see label)|
IMPORTANT: USE OF PESTICIDES – ALWAYS READ THE LABEL Pesticides must only be used for the purpose for which they are registered and must not be used in any other situation or in any manner contrary to the directions on the label. Never use a herbicide in any way contrary to the label recommendations. MORE INFORMATION: Includes “Noxious Plants of Australia”, by Parsons and Cuthbertson [Inkata Press]. DISCLAIMER: The information contained in this web site is based on knowledge and understanding at the time of writing. However, because of advances in knowledge, users are reminded of the need to ensure that information upon which they rely is up to date and to check currency of the information with the appropriate officer of North West Weeds or the user’s independent adviser. Les Tanner 30/07/15