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T.M. DeJong and K.R. Day

The relationships between shoot light exposure in one year and the flower and fruit production characteristics of those shoots the following year were indirectly investigated in summer pruned and nonsummer pruned peach [Prunus persica (L.) Batsch.] trees by evaluating leaf characteristics (leaf N and dry matter content per unit leaf area; Na and Wa, respectively) on tagged shoots during one season and the flowering and fruiting characteristics during the subsequent season. There were significant positive linear relationships between leaf Na and Wa on shoots in one year and flower and fruit production per unit shoot length during the subsequent year. Summer pruning had relatively little influence on these relationships. There was no apparent relationship between percent fruit set in the spring and light exposure of the shoots the previous summer. Following dormant pruning and commercial thinning, trees summer-pruned the previous year had higher yields than nonsummer pruned trees because of less shoot mortality and more fruit per tree.

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T.M. DeJong, K.R. Day, R. Beede, and R.S. Johnson

Current recommendations for fruit thinning of processing clingstone peaches in California suggest that growers delay thinning until an assessment of fruit size is made at reference date (10 days after first indications of pit hardening) and then adjust the crop load according to the fruit size attained. Recent research on modelling peach fruit growth indicates that delaying thinning until reference date (usually mid-May) can substantially limit final fruit size potential and crop yield when initial fruit set is heavy. In 1991 we initialed a field study to lest these model predictions and evaluate the yield response and economic feasibility of fruit thinning within 50 days of bloom to a specific crop load. The experiment was conducted in commercial orchards of the extra-early maturing cling peach cultivars Loadel and Carson. Three thinning treatments involved thinning different sets of trees on April 10, April 30, (∼30 and 50 dafb) and May 23 (reference date). Although costs of thinning at the earlier dates were 140-290% of thinning at reference date the increase in yield resulting from early thinning more than compensated for the higher thinning costs. There were no major effects of thinning treatment on the occurrence of split pits or other quality characteristics. This research has stimulated a re-evaluation of commercial fruit thinning practices used for clingstone peaches in California.