The Sicklepod Dilema

Image: (Above Right) Keith Macdonald, (Above Left) Cape York Weeds and Feral Animal Program.

Sicklepod (Senna obtusifolia) is a native to South America that arrived in Cape York in the 1970’s. It is used internationally as a food source and has several medicinal uses, however, in Australia, Sicklepod is a Class 2 declared pest plant.

Sicklepod and foetid senna ( Senna tora) are closely related annual weeds, very similar in appearance, and often found together. However, it is Sicklepod ( S. obtusifolia) that appears to pose the greatest threat to Cape York’s environment and economy. Sicklepod’s preferred habitat is well-drained fertile soils, grasslands and disturbed areas such as roadsides, drainage channels and overgrazed pastures. It is often found in dense swards along rivers and the edges of wetlands and floodplains.

There is some indication that Sicklepod infestations can degrade native habitats, particularly grasslands and riparian zones, through competition with native species. For agriculture, infestations can completely take over pastures, crops and roadsides and can block access to rivers. Though not generally palatable to cattle, the plant is poisonous and known to be fatal (Queiroz, Gustavo R. et al., 2012). Infestations of sicklepod have also taken over camping and recreation areas on Cape York.

Sicklepod seeds are spread by livestock, water, machinery, vehicles and footwear. Seed reserves of 2000 seeds per square metre of soil have been recorded in dense stands and seeds can germinate at any time of the year under favourable conditions. While research suggests that the seed can remain viable for up to 10 years, there is conflicting anecdotal evidence from Cape York’s weed experts around seed viability.

The best control for sicklepod is prevention, but control is also possible through good pasture management, mechanical control such as slashing, appropriate fire management, reforestation and by herbicide control. In some instances, sicklepod has become so widespread that entire pastures are unusable, which then requires containment and prevention of further spread. For advice on how to control the weed, please contact Biosecurity Queensland.

There is a lot we still don’t know about Sicklepod on Cape York. Cape York NRM is building a distribution map of the infestations of sicklepod across the Cape. If you know of any locations, wish to find out more about the existing research, or have some insight into sicklepod, please contact Luke Preece on 1300 132 262.

Identifying Sicklepod (Senna obtusifolia) Senna obtusifolia is a highly competitive, fast growing woody shrub which grows between 1.5-2.5 metres high, and 1 metre wide. While it is normally considered an annual (lives only for one year), slashed plants can reshoot, flower and last another year.

S. obtusifolia leaves are divided into three opposite pairs (4cm long, 2cm wide) with rounded ends and wedge shaped at the end. The small yellow flowers grow to 1cm across with 5 petals. The seed-pod is slender (3-5mm wide) and sickle-shaped, growing 10-15cm long.

Because of the variety of pest and native sennas, sicklepod can be difficult to identify. More information
can be obtained by contacting Department of Agriculture Fisheries and Forestry or the Queensland Herbarium.