Encouraging Dormancy with Defoliation and Coordinating Budbreak with Dormant Oil Kitren Glozer, Chuck Ingels and Jenny Broome

 Dormancy begins with defoliation and ends with bud break  Lack of ‘good chilling’ results in straggly bloom, weak flower buds and poor leaf out  Buds don’t develop good vascular connections, so aren’t strong ‘sinks’ for nutrients and PGRs  Strategy to overcome lack of chilling includes ‘pushing’ trees into dormancy (chemical defoliation) and compensating for some of the chill requirement with dormant oil

How to measure chilling? The Dynamic Model was developed in Israel where there are also warm winter periods Unit of chilling = Chill Portion (CP) Chill hour model doesn’t adjust for heat cancellation Based on four trial years, the broad definition of chill hours as a requirement for ‘Bartlett’ pear should be considered as 56 to 66 chill portions for a minimum to adequate requirement, using the Dynamic Model, forced bloom in mid-winter and full bloom dates

When and Why to defoliate?  Fall defoliation may help to induce early dormancy  Inducing early dormancy may help to satisfy chilling requirement –Reducing some of the ‘need’ to chill –Shortening the dormant period  Fall urea applications increase cold hardiness in some crops

Defoliation treatments in  1% CuEDTA + 2% urea applied 0, 2, 4 CP  Earliest defoliation on 26 Oct, 0 CP –  fruit weight and firmness; no diff. in Brix –  #1 fruit and estimated total yield –  #2 fruit by approximately 50%  Defoliation on 3 Nov, 2 CP –slightly decreased rat tail flowers  All timings  #2 fruit, no  in #1 yields  Tendency to thin fruit most with earlier defoliations

Fall Defoliation Chelated Copper + Urea = Fertilizer grade urea (2% v/v) and chelated copper (1% of Monterey Copper-All; Monterey AgResources Bartlett/Winter Nellis, planted in 1960 spaced at 12’ x 20’ (182 trees/acre) on the Polder Ranch Orchard on Russell Road. The soil was Columbia silt loam over Sacto silty clay CRBD, 3 blocks, 1 acre = 5.5 rows, total trial ~8 acres xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx = Untreated = Defoliant at 3 CP ( ) = Defoliant at 1 CP ( ) = Defoliant at 7 CP ( )

Fall Defoliation Results, 2 trial years Defoliation treatments in 2006 and 2007 Slightly delayed primary bloom thinned primary bloom improved fruit size and yield (more than doubled %crop picked at first harvest) later defoliation more beneficial (3-4 CP in 2006, 7 CP in 2007) Defoliation in 2007 at 7 CP thinned rat tail bloom This may be a tool to manage harvest timing and reduce the number of picks reduce cullage Reduce frost and fireblight risks No phytotoxicity

Dormant Oil Timing for Control of Bloom  Timing of dormant oil is usually mid-Dec to Jan 1 for convenience  This doesn’t account for state of dormancy in the tree and how much chilling has accumulated  Polder Ranch, trees planted 1960 and 1970; 10’ x 20’ (218 trees/acre)  Clean Crop Dormant Plus applied in CRBD, 3 reps of rows each (rows varied from 207 to 408 trees per row)  timings for dormant oil applications: Dec 31 (35 CP), Jan 7 (40 CP), Jan 14 (45 CP)  Collected bloom data (primary bloom, rat tail bloom) and yield data

Trial Trial  23 Dec, 30 CP  #1 & #2 fruit,  total yield and  Brix (too early)  Rat tail flowers reduced by treatment at 43 and 54 CP (2 last timings)  Yield decreased in the first pick with oil at 35 CP, Dec 31 (too early)  Yield ↑ in the first pick with oil at 40 CP, Jan 7  Oil at 45 CP  fruit per tree by 80 to 100 fruit, both for #1 and #2 fruit

Where to get chill data and information about calculating chill portions  Fruit and Nut Center Website (How-to Guide on the Dynamic Model and dataloggers)  Your farm advisor!

Acknowledgements Our appreciation to our grower cooperators Joe Green Ranch Greene and Hemley Ranch Van Loben Sels Ranch and to the California Pear Advisory Board for ongoing support