Bob’s Blog: Budburst, grape expectations & a warning

Over how many millennia have the expectations of grape growers been raised by the first appearance of leaves on their vines. The sign of a new vintage and all that implies. We share a common experience with the ancient Assyrians, Egyptians, Persians, Greeks and Romans and all who lived around the Mediterranian sea.Wine played an important role in early western civilization, indeed the Greeks followed their God Dionysos – God of winemaking, grape harvest, and fertility, from the 7th century BC or possibly earlier. The Mycenaean Greeks some 1500 years BC and in ancient Crete traces of the cult of Dionysian followers have been found.Importantly the vines traveled from the fertile crescent in the Middle East to Greece, and all ports west as our civilization developed. Interest in the vine continued to the New World, even the First Fleet brought Vines to Sydney.

The movement of vines seemed a safe thing to do until interest in North American grapes led to their transportation to England and then Europe. A new device to transport live vines across the ocean rather than cuttings was employed. Unfortunately along with these grapes in the soil came a bug, known as phylloxera, which eventually wiped out the native vines of Europe. So when we see our Hunter vines bursting anew we are all aware of the enormous risk they carry from the potential infestation.

There is something truly remarkable in the development of the grapevine buds. These buds develop in the previous season a period known as ‘Conditional Dormancy’ which later translates to “organic Dormancy” in Autumn – a time when no matter what, the buds won’t burst. In preparation for winter, the vines shut down, reducing their water content and building soluble proteins in the bark. They also undergo adjustments to withstand temperature changes but are capable of some basic metabolic functions using the energy from carbohydrates stored in the roots, trunks, and cordons. This is why it is important to look after the vines after harvest, enabling the build-up of starches to set the vines up for budburst.Towards the end of winter, the air temperature starts to rise and this is paramount in effecting budburst. Higher temperatures in late winter can advance the onset of Budburst as we have seen in the last few years. Budburst is positively correlated with soil temperature. Interestingly each varietal has its own inbuilt mechanism for responding to the summation of temperatures from mid-winter and to soil temperature. This leads to budburst occurring in Sangiovese and Chardonnay earlier than Semillon and Shiraz and then Cabernet Sauvignon being some 3-4 weeks later.

Depending on the vineyard site, minor adjustments can be made. In frost prone sites, the timing of the winter pruning later can delay budburst till the risk of frost has gone.In the Hunter, a summer rainfall challenged area, we start our spray programme at this time. Prevention being better than attempted cure.A timely warning was delivered at a recent Spring Vine Health Day by the department of primary industries in the Hunter Valley about the risk of phylloxera with the chilling example of what has very rapidly happened in the Yarra Valley.Back in the mid-1870’s when the aphid-like bug appeared in Victoria, the Yarra was spared but now it is active right in the heart of the valley. The 2017 boundary extension is the sixth expansion of the original Maroondah phylloxera infested zone (PIZ), which was established in 2006.

At the time of its arrival in Australia, it wiped out the vineyards of Sydney including my families Smithfield vineyards, and much of Victoria. The Hunter was spared as was South Australia and as a result of many commercial vineyards still are at risk being planted on their own Vitus vinifera rootstock..Throughout Europe and California, the vast majority of Vitis vinifera vines are grafted onto American rootstocks to protect them from the bug, as this rootstock is resistant to it.For those unfamiliar with it, the little yellow bugs develop a crawler stage and are active in the summer months. It can be spread via clothing, footwear, vehicles, vineyard equipment and machinery and on grapevine material.

Biosecurity has become an important issue with respect to our industry. We are at risk from the accidental transfer of the bug into our Hunter Phylloxera free zone and with Sydney being so close and visitations being encouraged the chances of infection increase.There has been an enormous increase in the cost of production in the Yarra for example. Vineyard owners, wineries, contractors and those who work for them have a heavy responsibility. All machinery, including contracted harvesting equipment, must be cleaned and disinfected prior to moving between properties.Disinfestation procedures include hot water treatment (2 mins at 70C), steam (above 100C), or dry heat (75 mins at 45C, or 2 hours at 40C). Picking bins and buckets have to be cleaned and disinfected and sharing of equipment becomes difficult. Heat treatment sheds have to be built to carry out some of these processes.In the Yarra, documentation is required for the movement of grapes and grape materials, machinery and equipment, diagnostic samples, soil, cuttings, rootlings, and potted vines.Owners must ensure all people who visit their property, clean and disinfect their footwear on entry and exit, in accordance with the “Footwear and Small Hand Tool Disinfestation Protocol.”I have heard various estimates, but the cost so far is estimated to be over $150m and could be up to $700m if the valley eventually needs to be replanted!So, it is time to reassess our biosecurity risks here in the Hunter; plant material coming from a phylloxera area, compost not properly heat treated, machinery moving from phylloxera areas and people visiting our vineyards not disinfecting their shoes etc. More than ever we are at risk as we encourage people to come and enjoy the life of the vineyards – a double-edged sword.Those signs warning about plant material on the outskirts of the winegrowing area are not really enough anymore. Vigilance and a careful review of possible threats should be on everyone’s to-do list.So bud burst heralds another season of grape expectations, and along with the ancients we look on the new life entering those much-traveled vines and guard against the threats which accompany these most universal gifts that bring joy and happiness to all those involved.

I have used the following sources:

iti-notes; bud dormancy and budburst AWRI www awri.com.au

Phylloxera Management Zones in Australia; vinehealth.com.au

Photos of budburst by Neal Crisford

Phylloxera images Wikipedia

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Author: Robert Lusby AM ©Around Hermitage Association