The 2009 ASHS Annual Conference

Manipulating deciduous fruit tree bloom timing in temperate climates can spread the risk of crop loss from extreme temperatures.  Heavy rates of horticultural oil (4-5% v/v in 100 gallon/acre = 935 l/ha) applied in the dormant season can advance bloom in prune orchards in California.  Risk of phytotoxicity limits this practice.  Calcium ammonium nitrate (CAN17) fertilizer (25% v/v) plus non-ionic surfactant (NIS) at 2% v/v as a canopy spray in mid-winter (30-60 chill portions) can advance prune bloom in the Sacramento Valley of California.  Use of a nitrogen (N) fertilizer spray to break rest and advance bloom may be a viable alternative to horticultural oil for California prune growers. A field trial was established to compare the established CAN17 rate to two other commercially available N fertilizer materials – dry potassium nitrate (KN) and a 28-0-0 urea-triazone solution (UTS).  The KN and UTS treatments were applied at 5% w/w and a 1% v/v rates, respectively.  The three N fertilizer treatments, each applied with 2% NIS, were established in a randomized complete block design (n=4) in January, 2008 and January 2009 in commercial orchards near Marysville, California.  Additional treatments included horticultural oil (4% v/v) and an untreated control.  All sprays were applied between 50 and 54 accumulated Chill Portions.  Treatments were applied to individual trees by backpack mistblower at a spray volume per tree equivalent to 100 gpa (935 l/ha).  Separate orchards under similar management were used in 2008 and 2009.  Three small branches (< 2 cm diameter) equally spaced around each tree and containing 40-100 flowers each were flagged prior to bloom.  Open flowers were counted every 2-3 days through bloom.  In 2008, all rest breaking treatments advanced time of 50% full bloom by 5-6 days over the untreated control.  2009 data will be presented.