Likelihood of phylloxera being introduced into South Australian vineyards as a result of current flooding along the River Murray system assessed as negligible
Recent commentary in various media has speculated that River Murray floodwaters may transport phylloxera from flooded vineyards in the North East Phylloxera Infested Zone (PIZ) to South Australian vineyards. Vinehealth has assessed that this would almost certainly not occur* based on the situation to date. If factors contributing to this assessment change over time, or if new information comes to hand regarding the current situation, then a reevaluation would be warranted.
For phylloxera to establish in South Australian vineyards via River Murray floodwaters, all the following steps must occur. First, the floodwaters must reach vineyards infested with phylloxera in Victoria (pathway). Then, phylloxera must enter the floodwaters (entry). Then, it must survive the journey to South Australia along the River Murray and reach a vineyard (transport). And finally, the phylloxera must find a vine root and attach (establishment).
Based on the cumulative likelihoods for each of these steps, Vinehealth assesses that a phylloxera incursion in South Australia resulting from the current River Murray floods would almost certainly not occur*.
In making this assessment, Vinehealth worked with Professor Andrew Robinson (CEO, Centre of Excellence for Biosecurity Risk Analysis; The University of Melbourne), and Australia’s phylloxera researcher Dr Catherine Clarke (Research Scientist, Agriculture Victoria) to identify the steps and factors that would influence the movement and survival of phylloxera in floodwaters currently travelling from Victoria to South Australia.
Research findings, expert opinion and other intel was gathered for each of the steps listed below to inform an assessment, including:
- Pathway: Flood event details in Victoria’s North East PIZ
- timing of flooding
- area of vineyard flooded
- depth and duration of flooding
- level of phylloxera infestation in flooded vineyards
- Entry: Movement of phylloxera into the floodwaters in Victoria’s North East PIZ
- the phylloxera lifecycle stage present at the time of floods and its relative mobility
- impact of current cool, wet conditions on phylloxera population dynamics
- movement of floodwaters out of inundated vineyards
- Transport: Survival of phylloxera in water and distribution to South Australian vineyard
- phylloxera survival when submerged in floodwaters and in the absence of food
- travel time from inundated vineyards in Victoria’s North East PIZ to South Australian vineyards
- mechanisms by which phylloxera in River Murray floodwaters could reach South Australian vineyards
- Establishment: Viable phylloxera from the River Murray floodwaters establishing in a South Australian vineyard
- ability of a viable life stage present to attach to a vine root
- soil type of vineyards most likely to be flooded in South Australia
The assessment that a phylloxera incursion would almost certainly not occur at this time, is primarily driven by the fact that ‘hibernants’ would have been the only lifecycle stage of phylloxera present at the time of flooding in the North East PIZ. This is based on known phylloxera population dynamics and the cool seasonal conditions experienced. Root-galling phylloxera overwinter as hibernants, and they are strongly attached to vine roots. If these hibernants were physically detached from vine roots, they are unable to reattach and thus pose no threat. It is also extremely unlikely that the floodwaters would sever a portion of vine root with a hibernant attached to create an opportunity to enter the River Murray system.
Vinehealth will maintain a watching brief on all factors over coming months and reevaluate as required.
The expert assistance of Dr Clarke and Professor Robinson in undertaking this assessment is greatly valued and appreciated.
* Standard terms for describing the likelihood of an event occurring
| Likelihood | Descriptive definition |
| High | The event would be very likely to occur |
| Moderate | The event would occur with an even probability |
| Low | The event would be unlikely to occur |
| Very low | The event would be very unlikely to occur |
| Extremely low | The event would be extremely unlikely to occur |
| Negligible | The event would almost certainly not occur |