Articles
Bloom timing and fruit set of ‘Improved French’ prune following dormant application of horticultural oil or nitrogen fertilizers as rest-breaking agents
Article number
1260_19
Pages
117 – 124
Language
English
Abstract
Dormant-season use of high rates of horticultural oil (≥28 L ha-1) for pest control and rest-breaking (enhanced bud-break, bloom advance, and compression) is a common practice in Improved French prune (Prunus domestica L. Batch) orchards in the Central Valley of California, USA. Despite adequate chilling in most winters, traditional rationale for rest-breaking with horticultural oil has been the perceived need to shorten bloom duration while allowing more timely bloom fungicide application over large plantings with limited spray equipment.
Recently, crop losses associated with maximum temperatures above 28°C at bloom have prompted interest in advancing bloom.
High rates of horticultural oil can be phytotoxic to dry trees; consequently, there is limited use of rest-breaking rates of oil in prunes in drought years.
As rest-breaking alternatives to horticultural oil, dormant-season canopy sprays of N fertilizers were applied in mature, commercial prune orchards in the Sacramento Valley of California, USA, in 2008-2010. Separate treatments CAN17 + non-ionic surfactant (NIS), KNO3 + NIS, N-sure® 28-0-0 + NIS, Erger G® + CAN17, horticultural oil, or untreated control were applied to individual trees after 50-53 dynamic model chill portions accumulated (58-65 days before full bloom), and bloom progression and initial fruit set were subsequently measured.
In 2008 and 2010, all treatments significantly advanced bloom timing by 2-7 days and the percentage of fruit set increased or remained unchanged compared with the untreated control.
In 2009, only horticultural oil or Erger G® + CAN17 treatments significantly advanced bloom compared with the untreated control, and the percentage of fruit set was unchanged from the control for all treatments except KNO3 + NIS, which significantly reduced fruit set.
Horticultural oil provided consistent bloom advance (1-3 days) without fruit set reduction throughout the study, while CAN17 + NIS and Erger G® + CAN17 advanced bloom the most in any one year (6-7 days) with commercially acceptable fruit set.
Recently, crop losses associated with maximum temperatures above 28°C at bloom have prompted interest in advancing bloom.
High rates of horticultural oil can be phytotoxic to dry trees; consequently, there is limited use of rest-breaking rates of oil in prunes in drought years.
As rest-breaking alternatives to horticultural oil, dormant-season canopy sprays of N fertilizers were applied in mature, commercial prune orchards in the Sacramento Valley of California, USA, in 2008-2010. Separate treatments CAN17 + non-ionic surfactant (NIS), KNO3 + NIS, N-sure® 28-0-0 + NIS, Erger G® + CAN17, horticultural oil, or untreated control were applied to individual trees after 50-53 dynamic model chill portions accumulated (58-65 days before full bloom), and bloom progression and initial fruit set were subsequently measured.
In 2008 and 2010, all treatments significantly advanced bloom timing by 2-7 days and the percentage of fruit set increased or remained unchanged compared with the untreated control.
In 2009, only horticultural oil or Erger G® + CAN17 treatments significantly advanced bloom compared with the untreated control, and the percentage of fruit set was unchanged from the control for all treatments except KNO3 + NIS, which significantly reduced fruit set.
Horticultural oil provided consistent bloom advance (1-3 days) without fruit set reduction throughout the study, while CAN17 + NIS and Erger G® + CAN17 advanced bloom the most in any one year (6-7 days) with commercially acceptable fruit set.
Authors
F.J.A. Niederholzer, K. Glozer
Keywords
Prunus domestica, dynamic model
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