Canopy Management

Laterals or side shoots

Once a shoot starts to develop it may produce additional shoots from each leaf axil. These are lateral or side shoots and generally these must be managed to prevent overcrowding.

Commercial growers cannot usually afford the time to tend every single shoot and one of the main aims of the trellising method, soil and canopy management is to produce the maximum grape yield for the minimum cost - including labour cost. This means limiting side shoots and the rule of thumb is that the fewer nodes per vine that are left after pruning, the more they will tend to produce laterals. Unpruned vines produce the fewest side shoots and, indeed, this is one training method, but not one recommended for amateur growers.

The amateur is not so constrained and can pinch out or leave selected side shoots as required. With a newly planted vine it is customary to remove all side shoots in order to build up a strong shoot that will form the main stem of the vine. With a mature vine it is for the grower to decide how to treat the side shoots.

One year I returned from a brief holiday to find the leaves on my vines looking as though they had been machine gunned. I discovered that whilst I was away there had been ‘hailstones as big as golf balls’. To compensate, I allowed the laterals to develop and stopped these (i.e. pinched out the lateral leader) at just one leaf.

Another important factor to remember is that leaves are the ‘factories’ that produce the wherewithal for the plant to grow – including the sugars for the grape. A young leaf is created either from reserves stored in the plant or from products ‘exported’ from mature leaves. It is a waste of the vine’s efforts to create lots of side shoots (if these are not allowed to bear fruit). Even worse, the unwanted foliage may screen sunlight from the bunches and discourage ripening.

What is clear is that the lower the leaf is on the stem (i.e. the earlier it was created) the sooner it becomes a net exporter rather than an importer of photosynthesis products. Moreover, a leaf below the first bunch cannot shade the bunch (assuming the shoot is growing upwards), so it should be beneficial to allow one or at the most two leaves on the laterals below the first bunch. In practice, these get in the way of the developing bunches and if not removed can make harvesting more difficult. Above the bunch it is a matter of compromise – shaded bunches versus exporting leaves. The side shoot at the top of the full length shoot is the least likely to become a net exporter, but it is also the least likely to shade the bunches; so it is really a matter of experiment to see what produces the best results with your vines on your plot using your method of trellising. According to Smart a leaf needs about 30 days to become a net exporter – and that in warmer climates than the UK. Remember that untended laterals can very quickly cause shading and overcrowding that makes canopy management difficult and time consuming, so the simplest rule is to remove all laterals.

My personal practice is to remove all side shoots except the ones at the top which I pinch back to one or two leaves depending on where they are. New side shoots will develop and these are again pinched back to one or two leaves. This practice causes a ‘flower’ of leaves to develop at the top where they are exposed to the maximum sunlight without any risk of shading the bunches.

Some methods grow shoots downwards. In this case the above needs to be modified as appropriate.

Laterals do have one very useful property, however. Should the tip of a growing stem break, the top lateral will take over as the leader; this sets the shoot back, but the stem is not wasted.

Shoot thinning

Frequently more shoots begin to develop than are needed; this will lead to overcrowding. Extra shoots can arise from three sources:

  • ‘Spare’ nodes on a spur or occasionally a rod.
  • Multiple shoots from a single node
  • Water shoots – i.e. shoots that spontaneously erupt from old wood.

Excess shoots should be removed. It is best to do this in stages. Start early – soon after bud burst – and remove those shoots that are definitely not wanted; leave all ‘not sure’ shoots and remember shoots may be required for fruiting in the current season or as part of the development of the vine’s future shape. On the second pass – ideally when all risk of frost is past – remove all unwanted shoots. Subsequent passes should have to deal with water shoots only.

Tendrils

For the amateur it is wise to remove all the tendrils. It is much easier to manage, move and hence train shoots that or not tied by tendrils. Also it is easier when pruning. The time spent removing tendrils will easily be repaid. Once the tendrils are removed it is necessary to provide alternative means of support as without this the shoot would fall to the ground under its own weight.

I use professional grape clips rather than a twist of wire; they are much quicker and are reusable; you can get them from the shop!

Leaves are both a bane and a blessing. The blessing is that sugars are produced in the leaves. The bane is that they can shade the bunches and so prevent ripening. This is a major factor influencing the training method. If you enjoy blazing sun, only a few leaves are required; however, in the UK it is recommended that at least eight leaves should be left after the last bunch. The growing tip is then pinched out.

A few weeks before the expected harvest, remove the leaves surrounding the bunches. This allows the sun to get at the bunches and also allows air to circulate better and so discourage botrytis (grey mould) which thrives in humid conditions.

Wasps and Birds

Early ripening varieties may be troubled by wasps. Apart from the inconvenience of having them eat your produce, the punctured skins allow juice to seep out forming an excellent breeding ground for diseases including botrytis. There is no solution other than to plant a later variety. (I have experienced trouble with Madeleine Angevine, an early variety, but not with Seyval Blanc).

Birds are the biggest problem for the amateur. They are bigger than wasps and eat more and still leave damaged berries for disease. Expensive nets are the only real solution.

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