Insect Warriors fighting the Jane
Last spring and again this year, we have been confronted with purple paddocks and wondered where all these new Salvation Jane plants have come from, after years of finally being free of it.
We may also be wondering, what happened to the biological control agents that essentially obliterated Salvation Jane from the Hills landscape?
It is important to understand that biological control is not an eradication program but just one tool, and it can take many years for the insects to reach their full potential and spread. Biological control requires more than one agent and for Salvation Jane there is a suite of four insects that have been released. Each insect attacks a different life stage of the plant.
TIMING CRITICALSalvation Jane loves a fire as it initiates the germination of hard seed in the soil and with limited competition, it flourishes. The mass germination after fire should be used as an opportunity to control the Jane to prevent seed set. This will have a huge impact in depleting the seed bank in the soil.
Once bio-control is established, there is a normal wave of fluctuation. You may get a favourable season, allowing the host plant (Jane) to increase, however the bio-control insect population will also increase as there is more for them to feed on. As insect numbers increase, the weed declines again. These bio-agents were so successful in suppressing Jane reproduction that the weed was rarely seen in the Hills, and the bugs had essentially eaten themselves out of a job!
WHAT TO DOThankfully, many of these beneficial insects were sitting dormant in the top soil over summer and actually survived the fire. However, it takes between two to three seasons for insect numbers to increase again and this is why we are seeing purple paddocks again.
So, while we wait for the insect numbers to build up again, our advice is to:
• Control the flowering plants to prevent seed set eg by slashing• Work to re-establish competitive pastures (or revegetation)• Monitor the Jane as the insects may already be there and just need time to build up again
The bio-agents are quite mobile so even if you can’t see much activity on a particular site, the insects will move in from surrounding areas.
If you would like help in identifying the insects or want to learn more about what you can do to control Salvation Jane on your property, please contact the Hills and Fleurieu Landscape Board.