Many fruit-bearing trees maintain a complete change of leaves, in a regular annual cycle.
Therefore, every year they are dormant and their branches are exposed without leaves for several weeks or months.
In a cycle of dormancy and shedding with awakening and blooming, they bloom for a short and defined period.
They are also characterized by a fairly regular period in which their fruits ripen.
The beginning of the shedding phenomenon occurs as a result of the influence of the external conditions on the tree, usually in fall and winter.
As a result of the shortening of the day and the lengthening of the night, a mechanism is activated in the tree that affects the photochromatic substances in the leaves.
The process of assimilation gradually stops and the nutrients in the leaves are transported and stored in the roots, trunk and branches.
At the end of the process, the tree goes into dormancy.
In the meantime, the connective tissue between the leaf and the branch weakens and it becomes a disconnection tissue.
In this situation, a slight movement in the wind is enough to cause the leaf to fall.
Many fruit trees have an internal genetic trait, which results in the shortening of the day to a decrease and changes in the level of the active growth hormone – gibberellin.
These trees, most of which came to us from northern regions (such as members of the Rosaceae family: apples, pears, plums, cherries), may enter the fall even before the climate cools at the end of autumn. However, the cooling almost completely stops the gibberellin activity.
In contrast, trees of Mediterranean origin (pomegranate, fig, strawberry and even almond) are even more affected by the shortening of the day and less by the cold of winter and therefore will wake up from winter dormancy when the day gets longer again in the spring.
Most fruit trees of northern origin will be able to break dormancy only after accumulating multiple cold doses in the winter.
In a hot winter, when enough cold doses are not achieved, the awakening of the trees goes wrong and is not uniform.
It is known that in plants there is a transfer of dormancy from extreme and upper growth apices to lower growth apices.
Therefore, the awakening of the tree from slumber begins in the high tops or those flower buds that are not inhibited.
That is, the apical and high buds have an “initial advantage” over the rest of the delayed buds.
How do the fruit trees wake up from dormancy?
In some deciduous fruit trees, the “ripening of the conditions” for the emergence of flower bulbs takes two years and the flowers appear on branches that are two years old or older and not on annual growth rods.
During winter pruning, it is therefore important to leave enough branches with bulbs that will bloom next season.
The growth hormones, under the influence of accumulated cold temperatures, undergo a change until they bring again (probably through their influence on the arrangement of the atoms in the molecules of the components of the dividing-reproducing tissues) a renewal of the activity of flowering and growth.
In order to get a uniform and abundant bloom and to break complete dormancy, several artificial means can be used.
This brings the tree to embalming and giving a lot of fruit and in a uniform period.
These measures are not necessarily cheap:
A. Trees from climate zones similar to our climate zones
B. Lighting to extend the day for dormant trees.
C. Prune apical tubers.
This leads to the transportation of gibberellins to the sub-vertices
and a more even “dispersion” of the growth between the buds
(without the delay caused by the Amiri bud – greater branching is
also achieved, for example, by pruning seedlings).
D. Spraying with substances that have a hormonal effect.
There are substances (such as “cytokinin” hormones, chemical
defoliants, “winter oil” in orchards) that cause uniform shedding and
entry into a necessary coma.
E. Use of substances (such as “gibberellins” hormones, certain nitrogen solutions, also ethylene-generating chemicals and “summer oil”) that cause a more uniform awakening and break dormancy.
Fertilization in deciduous fruit trees:
Sexual fertilization takes place in the flowers, when the pollen grains are transferred, by means of insects, an internal mechanism in the flower or by the wind and are absorbed in the scar (on the leaf) in the flower.
Following fertilization, the fruit develops.
There are species/varieties in which the embalming of the fruit is done parthenocarpically, for fertilization.
In order for the pollen grains to be absorbed, there must be genetic compatibility and availability, that is a sufficient amount of ripe pollen grains, exactly at the time corresponding to the ripening of the leaf in the flower.
In some fruit species, neighboring trees, sometimes of different varieties, are required for fertilization.
It is customary to plant several trees in close proximity, preferably of different varieties of the same species (for example: pear, almond, apple varieties).
Due to genetic reasons and the adjustment of the ripening time of stamens / leaves, the fertilization in the flowers of the same tree will be very small.
A single tree will yield very little fruit while two neighbors can give full crops.
Pests and damage to deciduous fruit trees:
There are various insects, in addition to the Mediterranean fruit fly, that are “fruit lovers”.
They first lay eggs inside the fruit while it is unripe and very small.
As the fruit ripens, larvae (‘worms’) will emerge from the eggs and eat the fruit from the inside. Therefore, harmful insects are dealt with already in the early stages of embalming the fruit.
Another group of pests are those that suck and/or eat leaves and fruit skins.
There are pests that burrow inside the leaf tissue.
A very deadly group of pests are especially beetles, whose larvae feed on the trunk, branches and roots.
Their damage to the bark or the woody material is evident in the secretion of dark resin on the tree or the appearance of sawdust around the trunk.
There are several methods to deal with pests and sometimes it is useful to combine them.
Wrapping the young fruits in bags, or wrapping the whole tree in an anti-insect net.
Biologicaly, by dispersing predators and parasites that reduce the pest population, and there are also fungi that kill pests.
Use of non-toxic insect repellents.
Dispersions of sterilized males, which disrupt the reproduction of the population.
Use of hormonal baits (pheromones), also in combination with traps.
Yellow adhesive plates – attract many insects.
Spraying chemical poisons, mainly against the aforementioned group of sucking pests.
Irrigation of the tree with insecticides, especially against burrow pests, which are difficult to eliminate by spraying.
Many injuries can be caused by fungi.
There are fungi that damage the roots and the trunk.
some damage the leaves and some that damage the fruit and leaves.
They are fought with fungicide sprays and with “soapy” or “greasy” substances.
It is important when the tree is injured by pruning or breaking, to apply wood paste to the wounds.
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