I will be visiting ‘my tree’ for the first time later this year but . Dr Valentino Valzano keeps me informed about what my tree is ‘doing’. All the trees are just awaking from a winter nap. The sun is warming the Salento soil in Puglia.
And it is time to prune 60,000 olive trees!
. In the coming days we will start with the Pruning Operations;
In mature trees, pruning is mainly required to renew the fruiting surface of the tree and achieve high yields, maintain vegetative growth of fruiting shoots, maintain the skeleton structure, contain tree size, favor light penetration and air circulation inside the canopy, permit control of pests and diseases, prevent aging of the canopy, and eliminate dead wood. Under certain circumstances, pruning can be required to alleviate the effect of abiotic stress, to re-form the canopy after damage by frosts and pests, to rejuvenate old or abandoned trees, and to adapt an obsolete training system to mechanical harvesting. In modern olive growing, the training system should permit easy movement of machinery in the orchard; little attention needs to be paid to specific tree shapes.
Cutting stimulates metabolism and growth, which makes the plant tissue more susceptible to plant injury. In mild climates, with no spring frosts, pruning can be started in winter. Pruning before bud break is risky in cold climates, however, because of the high probability of frost that may damage the remaining tissue and delay wound repair.
An advantage of pruning after bud break is that even the inexperienced grower is able to assess the number of flowers and the potential crop removed by pruning, whereas flower buds cannot be distinguished macroscopically from vegetative buds at or before bud break.
Waiting to prune until emergence of inflorescences is feasible in small orchards, but may be difficult to manage in large ones, where a longer period for pruning is necessary. Pruning should not be delayed until after full bloom, since it will remove tissues towards which nutrients and carbon reserves have already been remobilized, resulting in a net loss for the plant. Late pruning does not damage the plant but can reduce seasonal vegetative growth substantially.
Summer pruning is done during the growing season when the plant is actively growing. It is not common in cultivars used for oil and it is usually limited to the elimination of suckers and water sprouts. The timing of pruning also influences the plant response. Removing shoots at bud break results in much more vigorous growth of the remaining shoots than if the same operation is performed at the beginning of the summer.
INTENSITY AND FREQUENCY OF PRUNING
Before going into details about the intensity and frequency of pruning, it is useful to note that the current tendency is to prune olive trees as little as possible. Concepts of minimum pruning should be applied in all possible cases to reduce costs substantially and simplify pruning management. These concepts can be summarized as follows:
- Prune only the trees that need it.
- Reduce the frequency of pruning.
- Adopt free-canopy systems.
- Use irrigation and fertilization to stimulate growth and sustain fruiting.
Note, however, that minimum pruning does not mean neglectful pruning.
The intensity of pruning should also take the crop load into consideration. It is especially important because of the alternate bearing habit of the olive tree. In heavy cropping years, the growth of the tree is reduced, so pruning should be limited to the elimination of water sprouts and weak shoots. Alternatively, trees should be pruned more severely after years of low yields.
When trees are not pruned every year, the intensity should be increased.
Less frequent pruning reduces pruning costs and the need for skilled labor as compared to other types of pruning. In this respect, olive trees for oil production are exceptional in tolerating not being pruned every year without yield losses.
The most critical factor in deciding how frequently to prune olive trees is the rate of the current year’s shoot growth. If active growth is maintained, pruning can be postponed until the following year. Pruning every two years or longer can be more easily implemented in irrigated orchards, in fertile soils, and with trees planted at wide spacing. A biennial frequency can be adopted in the majority of cultural conditions, but intervals longer than three or four years are not always suitable. Otherwise, yields decline markedly, and at the end of the four-year cycle, pruning will have to be drastic, with consequences on the vegetative-reproductive balance of the tree. Cultivars with an upright habit and those sensitive to foliage disease are less suitable for infrequent pruning because the excessively thick canopy and upright growth will make harvesting and pest control more difficult and time consuming.