Deciding how much material to remove is often one of the big questions when pruning, and unfortunately there is no one-size-fits-all answer.
Pruning is all about managing vine vigour and crop potential, although frost risk is also a consideration for the timing of pruning and the amount of material to remove.
Early pruning tends to encourage earlier bud burst, which may then be susceptible to frosts. Many growers like to fill the fruiting wire with more buds than necessary, or leave sacrificial canes, as an insurance policy, removing excess material once frost risk has passed. This can be effective, but requires time and labour to go back through the crop, and care not to damage remaining buds.
When deciding how much material to remove, and retain for next year, charge counting is a useful indicator, in theory at least. The amount of buds to keep is based on a tally of the number and size of canes produced this year, however given the extra time it takes to count every bud, charge counting is often used more as a guide rather than an exact rule to follow for every vine.
Bud dissection is even more time consuming, but can provide valuable information about next year’s crop potential. It is widely practiced in New Zealand and Australia, although only a few large-scale UK growers do it.
Once buds are dormant from January onwards (before green tip), remove a few canes that are representative of those you would retain, then carefully dissect the bud straight through the middle. With a microscope of 10-50 times magnification it is then possible to identify the dormant inflorescences, giving an accurate measure of how many bunches buds are carrying.
It is time consuming and fiddly, but provides a good indication of the success of floral initiation, and can help pruning decisions – i.e. should you leave fewer buds because each one will yield well, or retain extra buds because they only contain one bunch, then focus more on managing those canopies?
Don’t push new vines too soon
For those with newly planted vines that have had strong growth over the summer and reached the top wire, it can be tempting to avoid pruning too hard and tie shoots down in an attempt to produce a crop a year early in the second season.
This is not recommended though, as root systems are still relatively underdeveloped and are unlikely to support a crop so soon. Preferably, in year two, remove any rootstock shoots and select the strongest canes, bringing them down to two buds plus the basal – the strongest cane becomes the trunk the next year.
Even leaving just a few strong vines to crop early – perhaps to dissipate that vigour – can cause more problems than it’s worth long-term, because vines are usually managed for uniformity. Trying to produce a crop from a few vines when nutrition, disease control, and canopy management is being tailored to those not cropping until year three may also let in more disease and exhaust young vines before they mature.
Also, young vines should be pruned as late as possible to mitigate the ‘warming effect’ and tendency for early growth that often occurs when using grow tubes.
Strict hygiene is essential to minimise the risk of trunk disease infection and spread between vines.
Ideally, clean secateurs with a disinfectant wipe after every vine. It is a quick, simple task that can significantly reduce the spread of fungal pathogens.
Try to avoid pruning in the rain, which increases infection risk. Cold, dry days are better, although beware that pruning below freezing can also induce trunk disease flare ups, particularly where large cuts are made.
If disease, such as Downy mildew, phomopsis, or trunk disease, has been observed, consider the carryover risks of mulching material around vines. In some cases, it may be necessary to properly compost material off-site to kill pathogens, then return material as a mulch later.
Finally, when making pruning cuts, always leave enough die back space to ensure any infection runs out of steam before it reaches the bud. In 2023, we saw die back extend further than for many years because damp conditions were perfect for infection spread once sap started flowing.
There are varying opinions on how much space to leave. Some prefer cuts closer to buds where stems are narrower and there is less surface area for infection, while others like to leave the diameter times two – especially when making large cuts off the crown. There is also a theory that cutting directly through a bud may be better as this is where the plant’s immune system is highest, and the vascular system growth is perpendicular to the internode vascular system growth at that point, even though the surface area is greater.