ORCHARD COOLING WITH OVERTREE MICROSPRINKLER IRRIGATION TO INCREASE FRUIT RUSSET ON 'CONFERENCE' PEAR

The efficacy of the use of overtree micro-sprinklers to increase fruit russet on ‘Conference’ fruit was studied over a period of 3 years. The objective was to increase fruit wetting at night by irrigating 1 mm/day. Irrigation was performed every day at midnight, from the end of petal fall, and for a period of 40 days. This strategy was compared to an untreated control and a standard practice consisting of making two applications of cupric hydroxide: at the end of petal fall and 1 week later. Applying micro-sprinkler irrigation significantly increased fruit russet compared to the untreated control in the first two years, but this treatment was less efficient than applying cupric hydroxide. In the last year of the trial, rainfall and relative humidity in April and early May were higher than in a normal year and this caused similar russet development in fruit of the control and overtree micro-sprinkler treatments. For all three years, the percentage of fruit in the extra russet category (with russet on over 50% of their surface) was 10% higher in the micro-sprinkler trial than in the untreated control (36 vs. 26%). However, cupric hydroxide increased russet to a higher degree: 75% of these fruit were assigned to the extra russet category (with russet on over 50% of their surface). Even so, applying copper did induce a reduction of over 25% in the final yield.