Thinning
In fruit growing, thinning is the term used to describe the removal of excess fruit from the tree during the growing season. Thinning can be done mechanically or chemically. Chemical thinning dominates the commercial expansion, which is only supplemented by mechanical thinning.
Thinning is done for three main reasons: (1) To remove small fruits that have no market potential. (2) to leave more nutrients in the remaining fruits. (3) Thinning prevents alternation .
Starting position
In fruit growing
In the case of pomaceous fruit, it is sufficient if around 5 to 7 percent of the fruit are ripe in order to achieve a so-called "full harvest". For example, apples already lose a significant proportion of their fruit when they fall in flower, fall in June and fall before the harvest. Even so, the nutrients from the entire tree are not enough to bring all of the fruits to their full size and aroma. Larger fruits, in which the proportion of core and shell in the total fruit is automatically significantly lower, achieve a higher market value and are therefore preferable from the grower's point of view. The ratio of leaves to fruits is important for the fruit size, with the largest fruits being produced at a ratio of around 100 to 1.
In addition, irregularities in the distribution of carbohydrates cause an alternation sequence. The thinning removes further fruits from the tree at an early stage in order to ensure an optimal harvest and to prevent alternation as far as possible. In the case of varieties that have a strong tendency to alternate, it may be that more thinning is required than would be necessary for an optimal harvest in order to reliably prevent the alternation from swinging up.
A special situation arises on poorly growing roots . Here the trees begin to produce fruit as early as the second or third year of life. This early shift of the assimilates into the fruit has an unfavorable influence on the growth of the young tree, which can only develop a weak crown due to the lack of carbohydrates there. In order to allow the tree to fully grow, the flowers on particularly young trees are completely removed.
In viticulture
In viticulture, thinning takes place in order to thin out overcrowded grapes. With some types of wine, compact, narrow-berried grapes can lead to poor ventilation and thus to moisture, with the result that the risk of mold within the grapes increases.
Period
Flower thinning
The earlier the thinning takes place, the greater its impact on yield and alternation. The flower thinning, the removal of flowers on the tree, is therefore the most important step in thinning today. However, if thinning is still in the flowering stage, unexpected late frosts can destroy further flowers and overall too little fruit can grow.
Thinning after flowering
If apples are thinned more than a month after flowering, it no longer has any effect on the alternation of the trees. For trees that actually have large fruits, thinning occurs relatively late to avoid oversized fruits. Because apples stop dividing around four to six weeks after flowering, what happens in those four to six weeks is particularly important for their final size. The larger fruit size and number of cells is mainly due to increased cell division when the tree is cleared.
Mechanical thinning
The oldest method used in fruit growing is mechanical thinning. Originally, surplus flowers or weakly growing fruits were knocked from the tree using mallets. This thinning "by hand" is carried out in a modernized form, and is, for example, in the cultivation of apples after harvest, the operation for which is used the second most time. Often today this manual thinning only takes place once a year late in order to readjust the previous chemical thinning.
In recent years, mechanical thinning has been gaining in importance again, as various widely used chemical thinning agents have lost their approval and no adequate replacement is available. For example, the Tree Darwin , which is mounted on a tractor, is widespread in Germany . On a vertical rotating spindle, plastic bundles hit the trees horizontally and knock out flowers. The technology can only be used sensibly between narrow trees with a crown diameter of up to 1.20 meters, as otherwise it would remove the fruit that grows well on the outside of the tree and leave the poorly growing, shaded ones inside the tree. The device was developed in 1990 by Hermann Gessler. The Bonn-type device is newer and has several horizontal spindles that are guided into the tree. The device is more cumbersome to use, but more flexible. In this way, wider trees, and thus other types of fruit than apples, can also be treated. For stone fruit there have been portable devices for some years with which even high crowns can be achieved. Here the spindle is attached to the end of a portable telescopic pole.
Chemical thinning
Chemical thinning emerged primarily from an effort to reduce the amount of work involved in thinning. In Germany, two methods are widespread: reducing photosynthesis to build up stress in the flowering period, or releasing ethylene to promote the detachment of the 10 to 24 millimeter large fruits. In the first method, the photosynthesis capacity of the tree is reduced by ammonium thiosulphate (integrated cultivation) or sulfur lime (ecological cultivation) during the flowering period . The tree gets stressed and sheds more flowers. The second method uses benzylaminopurine or ethephon (integrated cultivation). This leads to the formation of the already created separating layer at the base of the flower stalk, and to the separation from the fruit.
For legal and practical reasons, chemical thinning must take place in a relatively narrow time window. The effect of the means depends heavily on the weather conditions at the time of application, and the possible time window and suitable weather do not always coincide. Other substances used for thinning are naphthylacetamide , ammonium thiosulfate , benzylaminopurine and 1-naphthylacetic acid .
In viticulture, chemical thinning occurs primarily through the use of phytohormones , for example gibberellic acid .
consequences
Fruits from thinned trees are larger and more colorful. However, they are also more prone to some diseases such as specks , and may be more likely to suffer from calcium deficiency. The fruits also tend to be less firm. In 2013 apple cultivation in Baden-Württemberg was around 1000 to 2000 euros / hectare, which could be increased by thinning.
history
The oldest written sources, which report of surplus fruits and their mechanical reduction, come from Theophrastus of Eresos from the 4th century BC. In the 20th century, it was recognized that early thinning reduces the tendency to alternate during flowering. The first large-scale attempts at chemical thinning were made in the USA in 1934 by Auchter and Roberts. The chemicals of this time not only thinned out the fruits, but also caused defoliation and damage to the remaining fruits.
The first large-scale commercial thinner was Elgetol , which had been used regularly since the 1940s. In 1990 this substance lost its approval by the Environmental Protection Agency in the USA .
literature
- Ross E. Byers: Flower and Fruit Thinning and Vegetative: Fruiting Balance in: DC Ferree and IJ Warrington (eds.): Apples. Botany, Production and Uses. CABI Publishing 2003, ISBN 0-85199-592-6 . Pp. 409-436
Remarks
- ↑ a b c d e Lutz Damerow, Michael Blanke and Peter Schulze Lammers: Research report 143: Regulation of the density of the fruit cover in pome fruit growing (PDF; 579 kB) , Rheinische Friedrich-Wilhelms-Universität Bonn Faculty of Agriculture, Chap. 1.1
- ^ A b c Ross E. Byers: Flower and Fruit Thinning and Vegetative: Fruiting Balance in: DC Ferree and IJ Warrington (eds.): Apples. Botany, Production and Uses. CABI Publishing 2003, ISBN 0-85199-592-6 . P. 410
- ^ A b Ross E. Byers: Flower and Fruit Thinning and Vegetative: Fruiting Balance in: DC Ferree and IJ Warrington (eds.): Apples. Botany, Production and Uses. " CABI Publishing 2003, ISBN 0-85199-592-6 . P. 413
- ^ A b c Ross E. Byers: Flower and Fruit Thinning and Vegetative: Fruiting Balance in: DC Ferree and IJ Warrington (eds.): Apples. Botany, Production and Uses. CABI Publishing 2003, ISBN 0-85199-592-6 . P. 411
- ^ A b Ross E. Byers: Flower and Fruit Thinning and Vegetative: Fruiting Balance in: DC Ferree and IJ Warrington (eds.): Apples. Botany, Production and Uses. CABI Publishing 2003, ISBN 0-85199-592-6 . P. 414
- ↑ a b Erwin Haas, Christian Roschatt, Wolfgang Schweigkofler: Chemical thinning in viticulture , fruit growing viticulture 2/2009 pp. 80–82
- ↑ a b Michael Zoth: Thinning pays off ( Memento of September 26, 2015 in the Internet Archive ) , BWagrar 14/2013 pp. 34–35
- ↑ a b c Albert Widmer, Michael Gölles, Reto Leumann: - Mechanical thinning in fruit growing ( Memento from May 4, 2014 in the Internet Archive ) , leaflet 1-02-001 of the Agroscope Changings-Wädenswil ACW research station
- ↑ Thin out by machine with the right twist
- ↑ Bernhard Torggler: Suggestions of the advisory ring on fruit thinning (PDF; 215 kB) , Obstbau Weinbau 2/2009 pp. 71–73
- ↑ Ross E. Byers: Flower and Fruit Thinning and Vegetative: Fruiting Balance in: DC Ferree and IJ Warrington (eds.): Apples. Botany, Production and Uses. CABI Publishing 2003, ISBN 0-85199-592-6 . P. 415