Does Thinning of Old Apple Trees Improve Fruit Quality and Decrease Pest Incidence?

Abstract

The effect of thinning on fruit weight, color, biochemical composition, and on leaf insect occurrence was studied in an over 80-year-old orchard on two apple tree (Malus domestica Borkh.) old cultivars: Liivi Sibulõun and Paide Taliõun. The study was conducted to restore an old orchard for quality apple juice production. Pruning led to a significant increase in pests, but the number of natural enemies of pests and of neutral insects did not increase. The total number of arthropods was significantly higher on ‘Paide Taliõun’ in the second year after pruning. Consequently, more pests were found in both experimental years on this cultivar. Pruning significantly increased leaf SPAD value leading to a decrease in the total phenolics content of the fruit. The effect of thinning on ascorbic acid content was cultivar dependent. Fruit skin was greener, apple flesh color was yellower, and fruit weight increased by up to 60% after pruning. Among apple taste parameters, the sugar acidity ratio was not influenced by pruning but was positively correlated with skin color, especially in ‘Liivi Sibulõun’. Thinning of old apple trees does not affect the taste of apples but could reduce the impact on the healthy parameters, such as phenolic compounds.