The need and desirability to prune or control the growth of mature avocado trees has been a matter of debate for many years. We have found that pruning does not increase fruit yield in Kenya. Continual and severe pruning generally stimulates vegetative growth at the expense of fruiting, so pruning should be done only when absolutely necessary. There are, however, situations in all avocado-growing areas where tree control by pruning is necessary and desirable.
Reasons for Pruning
- To reduce harvest costs. Increasing harvest costs are becoming a major factor in avocado production. Fruit produced in the tops of tall, upright trees are more difficult and costlier to harvest. It is questionable in some cases if the cost of harvest is compensated by the return. Reducing and maintaining the height of the tree at an economical level is a practice followed by many even though the total crop may be reduced.
- To prevent wind damage. Major damage and breakage may be prevented in areas of extreme winds by lowering the height of fall-growing cultivars.
- To allow more effective pest control. More efficient and effective spray coverage may be achieved where there is less congestion between rows and when tree heights are not excessive, so pruning may be justified in areas which require chemical pest control.
- To permit effective irrigation. Some pruning may be necessary in orchards that are sprinkler-irrigated to assure a uniform water-distribution pattern. Low-hanging branches may interfere with the pattern of low-head sprinklers. These branches should be selectively removed. Similarly, overhead sprinklers may be obstructed by tall trees and tree height control must be practiced allowing uniform coverage.
- To permit cultivation and mowing. Low-hanging branches may interfere with cultivation or mowing where these practices are used. It is best to selectively prune the low branches rather than risk breaking them off accidentally with cultivation or mowing equipment.
- To delay crowding. The need to thin an orchard may be delayed for a year or 2 by selective removal of branches on temporary trees which will later be removed. This provides more illumination to permanent trees and prevents loss of lower foliage and production. Such pruning does reduce the yield of the temporary trees, but reduced production for a year or 2 is preferred to no production at all on the temporary trees.
Methods of Pruning
Selective pruning is accomplished by hand tools or power-assist hand tools in which the cuts made are individual and selective. This is preferred in most cases and is the only type of pruning adaptable to the terrain on which some avocado orchards are planted. Selective pruning, as the name implies, allows the individual selection of branches which are to be removed. It may be upright shoots or branches to limit or reduce the height of the tree,
overhanging side branches to reduce crowding, low-hanging branches which interfere with irrigation or other
cultural operations etc.
Prune sparingly and make cuts as close to a lateral branch as possible when such pruning is necessary. The greatest growth stimulation is nearest the cut. Removal of large branches will stimulate vegetative growth over the entire tree.
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Mechanical hedging and topping
Hedging and topping are non-selective types of pruning which are being used today by economic necessity. Relatively little topping and even less hedging has been practiced in Muranga. However, the use of hedgers and toppers in southern Florida for avocado tree control has increased in recent years and has become an accepted cultural practice.
Hedging and topping are done by large machines which are non-selective in their cutting but which remove growth at a lower cost. The lower cost of this type of pruning may well compensate the temporary loss of production that results and the repeated tree control necessary with the following regrowth. It should be noted that the vigor and productivity of avocado trees vary depending on the cultivar and climate in which they are grown. We are not sure that frequent non-selective cutting to control growth would be a sound or economical practice in climates and with cultivars such as we have in Muranga. More information is needed concerning these practices in other areas. Chemical growth inhibitors to retard the regrowth of pruned trees or to initially train them to a more compact size has been investigated. There are currently no satisfactory materials for use, even though some have shown promise.
Time of Pruning
Light selective pruning may be done at any time of year. Heavy pruning is best done after the crop is harvested but before late summer or early fall. Late pruning may stimulate growth.
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