[Apple chemical thinning]
1992
Gil S, Gonzalo (Universidad Catolica de Chile, Santiago (Chile). Fac. de Agronomia)
The use of chemicals is the only possibility to produce thinning early and fast enough to regulate cropping. Dinitros are caustic products that avoid fecundation on a proportion of flowers if they are applied at 80% anthesis. They are a good option for difficult to thin and alternate bearing cultivars if spraying can be done in that precise time and if blooming is uniform. Other products can be used 1 to 3 weeks after bloom. They enhance organ competition for nutrients stimulating their growth and metabolism, reducing photosynthesis, or producing stress via ethylene; the weaker fruits do not satisfy their needs, stop growing, and drop. Naphthalenacetic acid (NAA) is useful in cool and humid climates that favor its absorption whereas in other conditions higher doses that cause damage must be used. Because of its auxin nature NAA is also applied at full bloom for difficult to thin cultivars as it reduces seed number. Carbaryl is a reliable fruit thinner at a wide range of concentrations and under different conditions; it has been very effective for Spur Delicious in Chile. Its tendency to induce some russetting and to favor development of mite populations is controlled by mixing with NAA and reducing the rates of both chemicals. Benzyladenine appears as a new promising alternative. Ethephon is an effective product applied at many stages of development and concentrations, but the greatest benefit has been obtained at full bloom; it offers a good possibility for difficult to thin cultivars. Inhibition of photosynthesis by shade or terbacyl induces fruit drop, but it is difficult to regulate. Every cultivar grown in a given environment requires an specific standard of thinning. Actual recommendations from different parts of the world are summarized in a table
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