The advice comes from the NSW Department of Primary Industries (DPI) and Local Land Services (LLS).

NSW DPI weed biocontrol scientist, Andrew McConnachie, said buoyant conditions have seen a population boom in biocontrol agents, including crown and root weevils which can kill the weed.

"The weevils are back in force this spring, after drought conditions reduced biocontrol agent populations, and now they have the numbers to make an impact on weeds," Dr McConnachie said.

"We suggest producers inspect Paterson's curse infestations and look for small shot holes in rosette leaves, which are evidence of crown and root weevil damage.

"If you find holes in the rosettes, leave the weevils to do the job and don't spray Paterson's curse.

"Biocontrol agents will be without a food source and their numbers will drop if weeds are sprayed now.

"With the right population levels crown and root weevils can kill Paterson's curse plants and its close relative, viper's bugloss.

"Other biological control agents, a leaf mining moth and a flea beetle, help too by reducing the growth of both weeds."

Currently six established Paterson's curse biocontrol agents are causing significant damage to the weed and biocontrol remains an important component of integrated weed management programs.

Captions: Central Tablelands LLS regional weeds coordinator, Marita Sydes and NSW DPI weed biocontrol scientist, Andrew McConnachie find evidence of biocontrol agent damage to Paterson's curse plants near Orange.