Many a traveller has been seen taking photographs on the side of the road as the district’s canola paddocks have been in bloom over the last couple of months. As the Canola matures and turns from its vibrant yellow to a darker colour, attention has turned to the purple coloured plant which is also dominating a number of paddocks as well as road and highway verges.
It may be a nice colour of purple when contrasted against the canary yellow of the canola or the green grass it attempts to overcome however, the presence of this invasive pest can’t be understated.
Salvation Jane, Blueweed, Lady Campbell weed or the Riverina Bluebell are just some of the names given to Paterson’s Curse. It is supposedly named after the Paterson family of Cumberoona, New South Wales, who planted it in their garden in the 1880s.
It is estimated to cost Australian sheep and cattle producers $250 million through lost production in pastures, control costs and wool contamination.
The drought conditions have eased in the area over the last 12 months, however, the drought left little plant life in the soil. This provided a good starting position for the purple curse to entrench itself alongside the other plant life attempting to reinstate itself, including man made pastures and crops.
Paterson’s curse usually germinates in early autumn. Uncrowded plants develop into broad rosettes over the winter months. In dense infestations where plants are crowded, the leaves grow upright. Rosette leaves grow from 10-35cm long and are oval to elongated with distinct lateral veins.
Paterson’s Curse near the border of Yass Valley Council and Hilltops Council.
In spring, the plant produces one or many erect branched stems from 20-200cm tall. Stem leaves are narrow and smaller than the rosette leaves.
The whole plant is covered with tiny stiff bristles that may cause skin irritation when handled.
The 2-3cm long flowers are mostly purple but occasionally pink or white, and shaped like a curved trumpet.
The ‘curse’ is a prolific seeder that can produce more than 5000 seeds per plant per year. Large quantities of seeds may accumulate in the soil over several years.
Paterson’s curse contains pyrrolizidine alkaloids. These alkaloids cause liver damage if livestock graze the weed for extended periods. Liver damage reduces livestock productivity, reduces their productive lifespan (increasing stock replacement rates) and may result in death. The damage is irreversible and cannot be treated.
It has been observed that the production of pyrrolizidine alkaloids in Paterson’s curse increases at the full flowering stage. This suggests that the weed is the most toxic to livestock if grazed while it is flowering. Further research is being conducted to confirm this trend.
Susceptibility to poisoning by Paterson’s curse varies with different livestock species. Pigs and horses are highly susceptible, cattle moderately susceptible and sheep and goats the least susceptible.Pigs and horses are non-ruminants and do not have the necessary micro-organisms in the stomach to break down the pyrrolizidine alkaloids.
Individual horses vary in their susceptibility, with some dying after a few weeks grazing Paterson’s curse. Others may graze the weed for successive seasons before signs of poisoning appear. There is usually a gradual loss of condition over four to six weeks followed by listlessness and poor appetite. Some horses show nervous signs such as head pressing, blindness and aimless walking. This is because toxins, normally removed by the liver, build up in the bloodstream and interfere with brain function. Most horses die once the illness is apparent, even after being removed from Paterson’s curse infested pasture. On post-mortem the liver appears small, firmer than normal, and fibrotic. Jaundice of the carcase and an excessive amount of yellow fluid in body cavities can also be expected.
Although pigs are highly susceptible to pyrrolizidine alkaloids, Paterson’s curse poisoning is rarely encountered in today’s intensive piggeries: it only occurs where pigs have grazing access to the weed or when they are fed grain contaminated with Paterson’s curse seed.
Cattle are moderately susceptible to pyrrolizidine alkaloid poisoning because the rumen (first stomach) contains micro-organisms which can break down the alkaloids before they enter the liver and cause damage. However, if they are forced to graze large quantities of Paterson’s curse for long periods an ill-thrift condition due to liver damage may result. Cattle lose condition, may scour, waste away and die. On post-mortem, livers are characteristically hard, small and fibrotic.
Sheep and goats are relatively resistant to pyrrolizidine alkaloids because the rumen breaks down the alkaloids, and the alkaloids are metabolised in such a manner that products are produced that are less toxic. However, if sheep graze Paterson’s curse over several years some liver damage will occur and the damage will cause copper to accumulate in the liver. In sheep, under certain conditions, the copper is suddenly released into the bloodstream, resulting in death. This condition is called chronic copper poisoning.
There are numerous ways to deal with Paterson’s Curse. Local Land Services is finding success with a little weevil which is having a big impact. Adult weevils disperse to young plants of Paterson’s curse, feed on the leaves which causes the ‘shot hole’ damage and then lay eggs in the growing crown of the plant. Larvae hatch from the eggs and head towards the crown of the plant and top of the root where they can cause enough damage to kill the plant.
Picture – A McConnachie, NSW DPI
Most damage is caused by larvae feeding in the crown during autumn, winter and spring. Plants under heavy attack may die before seeds can be produced.
The larvae of both weevils can often cause significant damage to Paterson’s curse resulting in plant death with 10-20 larvae per plant being capable of killing rosettes up to 20cm in diameter. For more information on what you can do to control Paterson’s curse, contact your Local Land Services team.