Evaluation of Lime Sulphur as a Thinning Agent for Pears

Garriz, P.I., Alvarez, H.L., Colavita, G.M. and Gajdos, M.S.
Faculty of Agriculture, Comahue National University, Argentina

Organic foods are produced using agricultural methods that emphasis conservation of renewable resources. Thinning is a central management activity in the production of high quality fruit required for the domestic and export market. Finding an organic blossom thinner is a major challenge as hand thinning is a costly practice. Furthermore, early thinning of fruit trees is important since it influences fruit size in the year of application and affects flower bud formation for the following season.

At the High Valley region of Argentina (lat. 38°56’ 67°59’W), lime sulphur was evaluated as flower thinner on ‘Abbé Fetel’ (Pyrus communis L.) pear trees trained to palmette leader. Treatments were 1) control, and 2) 7 % lime sulphur applied at 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, fruit weight was determined with an electronic scale and the maturity indices were measured. Fruit was then graded into size categories. Growth equations were developed with SYSTAT procedure and mean separations were computed with Student’s t-test.

The lime sulphur sprays significantly increased mean FD, starting from 115 DAFB. Logistic models best fitted the fruit growth vs. time curves. Treatment 2 increased final fruit weight by 16.5 %, as compared to the untreated pears. Percentage of fruit <65mm was 25 % for the control and 5.26 % for treatment 2. 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.

Consequently, our data indicate that the application of lime sulphur at 7 % was an effective practice to thin flowers of ‘Abbé Fetel’ pears.