Grapevine pruning is one of the most important management practices in the viticultural ‘toolbox’ that helps to achieve the viticulturist’s dream of vine balance. Vine balance is basically the appropriate balance between vegetation and fruit production to achieve the level of yield, fruit maturity and tannin/flavor/color development desired in the grapes.  With too little vegetation, the vines may not have the capacity to ripen the fruit, and with too much vegetation, the fruit can be shaded, the vine focuses on producing more vegetation and does not focus on fruit ripening, and again the fruit can be perceived as under-ripe or dilute and green.  Another main reason to prune is to localize the fruit into an area that will be easy to manipulate for sun exposure, disease control, and harvest.

In a vine, all of the dormant buds which are located at the base of every leaf node are potential growing points for the following season.  If we do not prune, all of these buds will start to grow in the spring, and since there are so many of them, they will compete with one another and not grow very vigorously.  As a result, there will be lots of weak shoots and fruit everywhere.  It will be hard to ripen the fruit, create uniform sun exposure, and control diseases with the fruit spread all over the place.  If we prune too hard, and leave too few buds, these positions will grow so vigorously that they will continue to grow and grow, often forgetting to focus on ripening the fruit.

There are two main types of pruning systems: cordon and cane pruning.  With a cordon training system, there is a permanent horizontal extension of the trunk along the fruiting wire with spur positions where the desired buds will be located.  With a cane pruning system, there is an annual renewal of one year old wood (the most fruitful buds come from one year old wood) along the fruiting wire.  Today we are going to discuss cordon pruning.

After many years of experimentation and knowledge accumulation in the industry, we have industry standards to determine how to prune.  Provided that the site is planted with the appropriate variety, rootstock, spacing, and trellising, there are several rules of thumb in regards to cordon pruning.  One is that the spur positions should be located about 5-6 inches apart from one another, allowing for approximately two positions per foot of cordon.  It is important to not crowd positions, especially where the cordon from one vine meets the cordon from the other vine, because crowded positions will lead to crowded fruit and ripening and disease control problems.

Another industry standard is to leave 2 buds per position.  If the vines are weak and the prior year’s shoots are thinner than a pencil, it is preferable to leave only one bud to focus the vegetative production into producing a stronger shoot.  If the vines are too vigorous and the prior year’s shoots are significantly thicker than a pencil, you may want to consider leaving three buds. However, three buds can crowd the fruit, and it is preferable to devigorate the vines using other means, such as reduced irrigation, less fertilization, permanent cover crops, and other techniques. 

Since last year we would have left a two bud spur, there are two shoots that have matured from each position.  It is advisable to cut and remove the top shoot completely.  The top shoot is chosen for removal in order to keep the spur position as low as possible.  Then, the lower shoot is cut down to a 2-bud spur.  Occasionally it is preferable to pick the top shoot to reduce crowding of spur positions. It is preferable to cut the shoot at an angle away from the nearest bud in order to prevent the sap that bleeds out of the wound from dripping on the bud and making it susceptible to rot. 

One main consideration during pruning is that pruning wounds are susceptible to fungal pathogens such as Eutypa lata, also known as dead arm, and Botryosphaeria species, also known as Bot canker.  These fungi are dispersed in the winter rains, and have higher concentrations earlier in the winter season than later in the season.  The vines are also more susceptible to infection earlier in the season. Therefore, it is advisable to wait as late as possible to prune, often in March in the California north coast regions.  If this is not practical, pre-pruning can be considered. Pre-pruning is pruning to a 4-5 bud spur to remove most of last year’s vegetation off the training wires.  If the wounds become infected, the fungus will not have enough time to move down the longer spur, and any infection will be pruned off during the final pruning later in the season.  Pre-pruning speeds up the final pruning, and pre-pruning can be accomplished with less skilled labor. 

It is best if pruning can be done during a block of weather with little or no rain.  It may also be advisable to treat pruning wounds to prevent Eutypa and Bot canker infections.  Check what materials are registered for your crop in your state and consultwith a licensed Pest Control Adviser before making any treatments. Make sure to follow all label instructions too! 

Happy pruning!  And check out the following video on cordon pruning!