Using bio-control for Paterson's curse
From the August 2008 edition of Agriculture Today.
Seven biological control agents for Paterson’s curse, all insects, have been released in NSW.
One of the first releases was the leaf-mining moth (Dialectica scalariella) in 1988 which is now distributed widely.
While the moth can be found in most districts causing damage to Paterson’s curse, it does not provide sufficient control on its own to drastically reduce the weed populations, but nevertheless places additional stress on them.
Perhaps the three most promising releases are the crown weevil (Mogulones larvatus), root weevil (Mogulones geographicus) and the flea beetle (Longitarsus echii).
These insects appear to have expanded their territories significantly from their releases sites and can be found across much of the southern and Central Tablelands and South West Slopes.
Both weevils survive summer as adults, living off body reserves until the following autumn when they seek germinating curse plants from February to April to feed on and start laying eggs.
Crown weevil larvae feed inside leaf petioles and head towards the crown of the plant and top of the root.
Larval damage is often seen as a dead growing point with black ooze.
Because the crown weevil feeds above ground it is susceptible to damage by grazing animals.
Late breaks, low rainfall, and hard grazing do not favour this insect and it may not be the dominant bio-control agent in closely grazed sheep pastures.
A newer strain of the crown weevil, the Portuguese strain emerges from its summer "sleep" about four weeks later than the original and widely dispersed French strain of the crown weevil and is more suited to areas that experience late and unreliable rainfall.
Root weevil larvae feed inside the root about three to five centimetres below the crown.
Larval damage is not seen unless the plant is dug up and the root inspected for tunnelling larvae.
Because the root weevil feeds in the root of Paterson’s curse it is less susceptible to damage from grazing animals.
The root weevil also emerges from its summer "sleep" about six weeks later than the French crown weevil and is also better suited to areas that experience late and unreliable rainfall than either strain of crown weevil.
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.
The flea beetle survives for up to six months over summer as pupae, emerging in early winter as adults.
The adults feed on leaves, causing small holes on the surface.
This feeding damage on Paterson’s curse is readily observed at present in many pastures.
The larvae hatch in winter and begin feeding on the taproot, slowing plant growth. Because much of the beetle’s lifecycle is below ground it is far less susceptible to grazing damage.
The over-summering ability and grazing tolerance makes this agent useful in years with late breaks and situations with heavy grazing. It is not surprising that it is dominant in many pastures.
Bio-control agents are unlikely to wipe out Paterson’s curse altogether but some of them can cause significant damage to weed populations and will be an important component of an integrated weed control program.
