With vintage well under way, it’s always good to stop and think about whether your use of grape marc could be putting your vines or another grower’s vines at risk.
Do you actively seek out grape marc to apply to your vines? This application brings with it the risk that the marc could act as a vector for transferring phylloxera into your vineyard or adding to your present pest load.
Vinehealth Australia strongly recommends that self-composted grape marc that has been sourced from vines grown in a phylloxera risk or infested zone, is applied with extreme caution to vineyard soil. A similar level of caution should also be applied to using commercially composted grape marc from these zones, unless you are very confident in the composting process to reach adequate temperature/time specifications throughout the piles to ensure pest kill1. Note, the importation of grape marc sourced from vines grown in a phylloxera risk or infested zone is prohibited in some states. Refer to your state’s Plant Quarantine Standard or equivalent for regulated movement conditions.
For growers deciding to apply marc that has been produced from vines grown in a PEZ and composted inside the PEZ, you still need to be aware that this marc could harbour other pests and diseases, which may not have been killed through the composting process.
As part of Vinehealth Australia’s review of the phylloxera-related Conditions in the SA Plant Quarantine Standard, we revisited the published science behind a range of sterilisation techniques currently available for items that can pick up and spread phylloxera. One such vector, being grape marc. According to the National Phylloxera Management Protocol, ‘marc must either undergo completion of three days (72 hours) of fermentation or composting or pasteurisation as per Australian Standard AS 4454.’
Our review concluded that fermentation studies conducted in Australia were old and undertaken using a very limited number of endemic phylloxera strains. These studies provided insufficient evidence that 72 hours of fermentation sufficed in killing our known range of key endemic phylloxera strains. Furthermore, we found that research on composting of grape marc as an effective sterilisation method for phylloxera is scant at best. Researchers noted difficulties even in commercial operations with maintaining and holding marc piles at a necessary temperature to ensure kill of phylloxera right through the piles, even with availability of proper turning equipment and temperature monitoring devices, let alone in a ‘backyard’ composting operation.
Our knowledge of endemic phylloxera strains and their ability to withstand increased temperatures has recently improved2, and this means that even higher temperatures need to be maintained right through these marc piles to ensure effective phylloxera kill. Some of this composting research was conducted nearly 20 years ago and involved an assumed upper thermal limit for phylloxera of between 36-40˚C. We now know the upper temperature of this range would need to be held for at least three hours to be effective.
If you are applying composted grape marc to your vineyards that has been composted in a commercial operation, ask for copies of temperature measured at various heights within the marc piles, to aid your confidence about the efficacy of the pasteurisation undertaken as part of the composting process. Theoretically, if grape marc is composted properly to AS-4454 it should not contain living pathogens such as phylloxera.
1 For example, 40°C for 3 hours or 45°C for 90 minutes.
2 Recent change of dry heat duration at 40°C from 2 hours to 3 hours