Background

What is the weed problem?

Stinking passionflower is an invasive environmental weed and also a weed of crops and pastures. It is one of the biggest weed threats to northern Australia. It is widely distributed from Shark Bay in Western Australia to northern New South Wales and is also found on many offshore Australian islands. The weed poses direct and indirect threats to native flora and fauna via overtopping and smothering of existing vegetation and terrain across protected areas, conservation areas, native forests, mine site rehabilitation areas and pastures. It has a variety of other negative impacts on social, environmental and economic values, with negligible positive impacts.

How the weed is currently managed?

Stinking passionflower controlled by uprooting, either directly, or during interrow cultivation and interplant hoeing. It cannot be smothered out, since it tolerates low light intensities and also tends to climb over taller plants. Grazing is unlikely to be effective due to the objectionable smell (and no doubt taste) of bruised foliage. The following herbicides are registered for use against stinking passionflower in Queensland, Australia: diuron + fluroxypyr, atrazine, atrazine + dicamba, fluroxypyr, and 2,4-D + ioxynil. However, chemical control is only worthwhile in graminaceous crops such as sugarcane or improved pastures, or where the herbicide can be directed away from crop foliage, since foliar application to broad-leaved crops would damage them.

What can biocontrol offer to the weed’s management?

Biological control is considered the only viable method of control for P. foetida in Australia because of the logistical difficulties associated with other control measures as well as the ecology and life history of the weed. Greater than 200 arthropods have been recorded on Passiflora species across their native ranges. These insects may offer promise as potential biological control agents.

Biological control of other Passiflora taxa has been practiced elsewhere (e.g. Hawaii), where natural enemies have been found to reduce up to 90% of the plant’s biomass. Given the low relatedness of commercial and native Passiflora species, and the known occurrence of putative specialist herbivores and pathogens, the prospects for biological control are promising for P. foetida in Australia.