Another factor to consider is cluster weight. Traditional spur pruning generally retains fewer nodes per vine than cane pruning. Thus spur pruning is useful for varieties with high crop weight production per retained node, and cane pruning is used for shy bearing varieties with small cluster weight. Disease susceptibility Fruit and the buds in the renewal zone tend to be produced in the same place. Shaded renewal zones also tend affect the micro-climate of the fruit zone.
Dense canopies restrict air flow, increase drying time and interfere with spray penetration.
For varieties which are sensitive to bunch rot, such conditions can spell disaster. This is the reason that the most valuable fruit is often Pendlebogen trained. When pendlebogen trained vines are vertically shoot positioned, summer pruned and given leaf removal treatment, their fruiting zones become very well ventilated. Such procedures are costly, but can substantially reduce fruit infection. Cheaper alternatives such as Umbrella Kniffin are compromises where fruit crowding is avoided by distributing the clusters widely over the trellis, and are suitable for moderately valued fruit.