In recent years machines for mechanical thinning of apple flowers have been developed in Germany, Switzerland and the USA.
- The crudest types of machine use a series of knotted ropes, which are dragged through the trees to knock off a proportion of the flowers.
- The ropes are attached at regular spacings to a curved beam which, using the tractor PTO, is lifted to be just above the tree canopy.
- The tractor is then slowly driven down the alley pulling the ropes through the trees and knocking off many of the flowers.
- The crudest machines, which drag knotted ropes through trees to knock off blossoms, cause considerable damage to the trees and cannot currently be recommended in the UK.
Trials conducted in Switzerland (Bertschinger et al., 1998) have focused on using what is known as the ‘wire-machine’ (designed by H. Gessler, Friedrichshafen-Hirschblatt, Germany).
- The machine is powered by and pulled by a conventional orchard tractor (Schröder, 1996).
- It comprises a vertically turning axle with nylon wires of approximately 40 cm long attached.
- The tractor is driven at approximately 4 km/h and the wires on the axle rotate at 1500 revolutions/min.
- Further details of this machine can be gleaned from Stadler et al., (1996) and from the UK importer N P Seymour.
- Use of the machine at the balloon stage of flowering reduced fruit set in orchards of Jonica, Golden Delicious, Maigold and Idared significantly (35%-65%).
- Thinning earlier at bud swell caused significant damage to the trees and thinning later at full bloom caused some deformations to the fruits remaining; thinning between green cluster and balloon seems the best timing for use of the machine.
Thinning efficacy was not adequate on pyramidal shaped trees with branches longer than 70 cm and this was especially true on the tree tops and in the centres, close to the central leader.
- Some increases in pests (aphids) and diseases were noted on the machine-thinned trees.
- The authors concluded that for machines of the type described to be effective, tree architecture must be adapted significantly.
- Slender cylindrical trees with short branches would be ideal.
- Further research is warranted on the development of orchard canopy systems and suitable machines for mechanised flower and/or fruitlet thinning in UK apple orchards.