TIMING APPLICATIONS OF DORMANT OIL IN ‘BARTLETT’ PEAR BY THE DYNAMIC MODEL

California pear growers use dormant oils for pest control and dormant bud stimulation, applying late December to mid-January.
However, bud development and full bloom dates differ year-to-year with variable weather cycles. “Delayed foliation” or irregular bud break caused by inadequate winter chilling results in lower yields, poor tree architecture, less uniform fruit size and makes orchard management practices (such as pest control) more difficult.
Rest-breaking agents are used in California cherry production with application timed by the Dynamic Model from Israel and chill portion accumulation, affording more reliable results than the “chill hour” model (hours ≤7°C). Winters in California are similar to those in Israel, with intermittent warm periods and frequently insufficient chilling.
Trials in 2004–2005 and 2005–2006 tested dormant oil applications at timings based on the Dynamic Model.
The bloom period was advanced and compressed and fruit size and total estimated yield improved by treatments within a certain range of chill portion accumulation; percentage of undersized fruit was decreased by 65–83%. The first year of trials was a ‘high chill year’, while the second was a ‘low chill year’. Defoliants applied in 2005 at timings based on early chill portion accumulation found defoliation on 26 Oct, 0 chill portions, delayed bloom development, increased fruit mass and firmness, with a reduction in the undersized fruit by approximately 50%. Defoliation on 3 Nov, 2 chill portions, advanced bloom and reduced production of secondary blooms (rat-tails), which were also reduced by some dormant oil applications.

VIII International Symposium on Modelling in Fruit Research and Orchard Management

K. Glozer, C. Ingels

Pyrus communis L., chilling, dormancy, chill model, chill hour, defoliant, chill portion, bloom, secondary bloom, rat-tail bloom

https://doi.org/10.17660/ActaHortic.2008.803.32