CROP LOAD MANAGEMENT OF TREE FRUITS IN THE PACIFIC NORTHWEST OF USA

Since 1998, the Washington Tree Fruit Research Commission (WTFRC) has conducted more than 300 replicated crop load management trials in commercial apple (Malus × domestica), pear (Pyrus communis), sweet cherry (Prunus avium), peach (Prunus persica), nectarine (Prunus persica var. nectarine), and apricot (Prunus armeniaca) orchards throughout Washington, testing 60 materials as apple chemical bloom thinners, including: caustic salts, growth regulators, photosynthetic inhibitors, plant oils, surfactants, particle films, fish byproducts, and weak acids and bases.
Results from trials on 11 apple scion cultivars on a range of commercial rootstocks clearly indicate lime sulfur was the most effective bloom thinner, whether applied alone or in combination with horticultural spray oils.
These programs consistently reduced fruit set, increase harvest fruit size, and promote return bloom in chemical bloom thinning trials and are acceptable in organic systems.
In apple postbloom chemical thinning trials, tank mixes of carbaryl and 6-benzyladenine (BA) produced similar responses more consistently than tank mixes of carbaryl and naphthaleneacetic acid (NAA). Serial summer applications of NAA and ethephon rarely increased return bloom in apple.
Gibberellic acid applications to reduce return bloom in biennial apple orchards showed promise.
Fruit size was increased by both BA and ammonium thiosulfate (ATS) in trials on three pear cultivars, even when fruit set was not reduced.
ATS and tergitol reduced fruit set and increased fruit size in Prunus trials, but results were inconsistent.

IX International Symposium on Integrating Canopy, Rootstock and Environmental Physiology in Orchard Systems

T.R. Schmidt, T.D. Auvil, I. Hanrahan, F. Castillo, J.R. McFerson

Malus × domestica, apple, Pyrus communis, pear, Prunus sp., chemical thinning, bioregulators, return bloom

https://doi.org/10.17660/ActaHortic.2011.903.105