Hormones such as auxin are normally moved from apical shoots to the root system to encourage root development. Pruning removes these apical shoots and as a result, decreases root development.
Manage soils & water to control tree growth & increase productivity (part 11)
Pruning (continued from last issue)
With fewer roots, cytokinin production is decreased. In addition, since total leaf area is decreased by pruning, fewer photosynthates are produced. These photosynthates are moved to storage areas of the tree, such as the root system. With less photosynthates produced, root growth is decreased.
Methods of vigour control that minimise the use of summer pruning, through better growth and fruiting balance, lead to more efficient fruiting canopies and therefore higher orchard performance.
Limited summer pruning still has a place for vigour control and particularly for rubbing out of vertical shoots on the upper surface of fruiting units.
Pruning fruit trees in winter invigorates the trees and can lead to excessive vegetative growth and shading which may worsen the quality of fruit and subsequent formation of floral buds. Summer pruning of excess regrowth can help avoid shading, but this is costly.
Unwanted shoots use (and therefore waste) photosynthates that could have been used to grow more and better fruit. Instead, you should rub out (not cut out) watershoots in late spring when they are still soft enough.
If a lot of summer pruning is necessary to keep the fruit trees under control there is something fundamentally wrong with management. The photosynthates being wasted in excessive summer pruning is better directed towards more or better fruit through altering the overall management to avoid this unwanted vegetative growth.
Pruning should be used more to direct growth rather than limit growth.
Generally, managing tree growth has focussed on either genetic means or on cultural practices of the tree (above ground). However, managing the growth of the root system is also possible through root pruning.
Root pruning has been used for centuries in order to decrease vigour of the fruit tree above ground.
This is the principle of bonsai plants. However, the results of root pruning of fruit trees are unpredictable and root pruning can also lead to weak trees, sunburn and small fruit.
In many ways, root pruning restricts the tree rather like hard soil does. The differences are that with root pruning the treatment is imposed once or at most twice in a season, whereas with methods of root restriction the inhibition of root growth persists all of the season and the conditions allow no compensatory new root growth.
High sustained production (cont. next month)
See this article in Tree Fruit JUne 2018