Fruit thinning is an important measure to guarantee a high fruit quality and a constant harvest over several years by avoiding biennial bearing. Apart from the market price, the amount of fruits and the percentage of first class fruits are key factors for the grower’s income. Furthermore, labour costs for hand thinning and harvest will be reduced with an optimal crop load. Therefore, fruit thinning is essential for the economic profitability of an orchard, mainly in apple production.
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In Switzerland, producers mainly use chemical growth regulators to reduce the crop load. Different registered thinning agents allow various strategies, depending on the variety, the weather, the experience of the farm manager and the risk of frost or fire blight. Most of the thinning agents influence the tree’s hormones (NAA, NAD, BA, and Ethephon). Potassium Bicarbonate burns the flowers. Metamitron reduces the photosynthetic activity, which finally leads to fruit drop. Apart from chemical fruit thinning, growers can also thin their trees by using mechanical devices (e.g. Darwin).
Since 2008, Agroscope focused their research activity on the efficacy of the new thinning agent Brevis. Brevis is registered in Switzerland since 2015 to thin apple and pear. Together with other research institutions in Europe, Agroscope investigates how the efficacy of Brevis can be predicted by the use of weather data. A second approach to improve the use of Brevis is by quantifying the efficacy shortly after the application by measuring the photosynthetic activity. These measures can help to estimate the influence on the crop load, which finally saves the amount of pesticides used in orchards.
Some new sweet cherry varieties tend to have a high crop load. For that reason, fruit growers would like to thin cherry trees to reduce the risk of biennial bearing and to increase the cherry’s fruit size. However, no chemical agents are registered in Switzerland to thin cherries now. Therefore, Agroscope evaluated different chemical products since 2004 to reduce the crop load of sweet cherries (ATS, BA NAA, Metamitron).
Agroscope has also executing functions on behalf of the Swiss Federal Office for Agriculture. Researchers of Agroscope write expertises on the efficacy of new thinning products.