Chemical thinning of apple blossoms in organic production

Abstract

An experiment on chemical blossom thinning on apple variety 'Summerred'/ M9 was performed in an experimental plantation in Brdo pri Lukovici. Different chemical thinners were applied on apple’s fruitlets in organic production. The experiment was designed in 7 randomized block with 13 treatments: 1. unthinned trees (as a control), 2. hand thinning in June, 3. 1% NaCl, 4. 1,5% NaCl, 5. 1% CH3COOH, 6. 3% CH3COOH, 7. 3% CaSx, 8. 1% rape oil, 9. 3% rape oil, 10. 3% of sunflower oil, 11. 3% soybean oil, 12. 5% dextrin, 13. emulsifier 100 + OCA 30. Chemical thinners were applied in a phenological stage at peak blooming with a manual knapsack sprayer. The best thinning of fruitlets (similar to hand thinned trees) was observed with 3% rape oil, however, relatively strong russeting of fruit skin was detected in this treatment. Statistically significant reduction of final fruit set also occurred when 1,5% NaCl and 3% soybean oil were applied, but with less fruit russeting.