Flower Thinning of the Pear Cultivar `Abbé Fetel' with Lime Sulphur

Abstract

Flower thinning of pears has advantages over fruit thinning in that the earlier it is performed the greater the potential effect on fruit size. At the Comahue National Univ. in Argentina (lat. 38°56' 67°59'W), lime sulphur was evaluated as flower thinner on 10-year-old `AbbAbbé Fetel' (Pyrus communis L.) pear trees trained to palmette leader. Cultural practices were similar to those of commercial orchards in the High Valley. Treatments were 1) control, and 2) 7% lime sulphur, applied on 16 Sept. 2002 (30% bloom) using an orchard sprayer. Fruit diameter (FD) was recorded two weekly (n = 20 per date and treatment). At 144 days after full bloom (DAFB), or initial commercial harvest, crop load, fruit weight and the maturity indices were determined. Fruits were then graded into size categories. Growth equations were developed with SYSTAT procedure and mean separations were computed with Student's t-test. Mean FD was significantly increased by the lime sulphur sprays, starting from 115 DAFB. Logistic models best fitted the fruit growth vs. time curves. The equation was: FD = 77.87/1+e2.26-0.03DAFB (R2 = 0.97), for the non-thinned trees. Treatment 2 increased the percentage of fruits ≥70mm by 42.16%. At 144 DAFB, thinned trees showed firmer fruits than the controls (64.4 vs. 61.7 N) and there were no statistical differences among treatments in soluble solids concentration and starch index; the values were 11.5 °Brix and 3.55, respectively, for the control fruits. Consequently, our data indicate that lime sulphur applied at 30% bloom was an effective practice to thin `Abbé Fetel' pears and to enhance fruit quality at ripening.