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Abstract
In each of three years, paclobutrazol was soil-injected at about a 15 cm depth and 1 m from the ‘Flavorcrest’ peach [Prunus persica (L.) Batsch] tree trunk. In the randomized complete block design, many significant differences between paclobutrazol-treated trees and controls were measured in the following categories: reduction of canopy growth, increased numbers of vegetative and floral buds in the lower portions of the tree, elimination of the need for summer pruning, increased hand fruit thinning time in two of three years, increased fruit yield and size, advanced fruit maturity, decreased leaf K, and increased leaf Ca. Paclobutrazol increased cumulative yield over controls from 30.1 to 41.8 t·ha−1 for the 3-year experimental period. This yield increase exceeded the controls by at least 22%, 71%, and 76% for 1984, 1985, and 1986, respectively, and occurred without measurable fruit quality loss, except for soluble solids, which were decreased in two of three years. Chemical name used: β-[(4-chlorophenyl)methyl]-α-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).
Various rates of Wilthin were applied at full bloom to limbs carrying 150 to 250 flowers to study their activity on blossom thinning of `Loadel' peaches. Wilthin applied at 0.75% and 1.0% significantly reduced fruit set to 29% and 30%, respectively, while the control produced 94%. The effectiveness of the 0.75% rate was dramatic, but it is interesting to note that the 1.0% rate did not lead to excessive thinning nor phytotoxicity on foliage or fruit. More extensive studies need to be done to fully determine the potential of this material. However, these results suggest that further testing of Wilthin on a larger scale is warranted.