Agriculture Reference
In-Depth Information
Effects of pruning
Pruning is carried out either in the dormant, winter, season or in the season
of active growth, when it is referred to as summer pruning. It is carried out
to develop a desirable tree framework and to maintain tree size to that which
can be easily sprayed, thinned and harvested: also to maintain fruit quality
by reducing the number of fruits, so increasing the size of those remaining,
and by facilitating light penetration, important for fruit colour development,
into the tree. In dormant-season pruning, shoots or older branches may be
shortened or removed entirely. Shoot shortening is called tipping or heading,
branch shortening is called stubbing or heading. Removal of complete shoots
or branches is referred to as thinning. In summer pruning leafy shoots may
be tipped or pinched, or removed entirely, i.e. thinned. The effects of these
treatments on shoot growth, reviewed by Mika (
), are as follows.
The individual shoots arising from a pruned branch are larger than those
on an unpruned branch.
The new terminal shoot following shortening of a branch is longest if
%
of the branch is pruned away.
For any given degree of pruning the size of the shoot growing from a pruned
branch is correlated with the length of the latter before pruning.
If the same amount of wood is removed, heading cuts induce more new
shoot growth than thinning cuts, largely because they release more buds
from correlative inhibition.
Despite the faster growth of individual shoots on pruned trees, the total
length of old branch and new terminal shoot is less than if no pruning has
taken place: pruning reduces the total size of the shoot system although it
stimulates the growth of new shoots.
Dormant pruning results in major increases in the levels of cytokinins,
auxins and, especially, gibberellins in the above-ground parts of pruned
compared with unpruned trees. These may be involved in the shoot growth
responses noted.
Summer pruning early in the season tends to result in the production of
a greater number of shoots than dormant-season pruning (Maggs,
).
Theearlierintheseasonthatsummerpruningiscarriedout,thegreaterthe
amountofregrowth:possiblyasaresultofthehigherlevelsofcytokininsand
other growth promoters early in the season and the build-up of inhibitors
late in the season (Ferree
et al.
,
). Late summer pruning results in
shorter shoots than on controls or winter pruned trees. Summer pruning
has a minimal effect on shoot growth in subsequent years (Marini and
Barden,
).
Summer pruning tends to lead to the production of spurs rather than long
shoots.
