Effects of Foliar Paclobutrazol Applications on Plant Growth, Yield, Quality, and Residue Levels in Greenhouse Cucumber Cultivation

This study evaluated the effects of foliar paclobutrazol (PBZ) applications at different doses and intervals on plant growth, yield, fruit quality, and residue levels in cucumber (Cucumis sativus L. cv. Olay F₁) cultivated under greenhouse conditions. The experiment was conducted using a randomized complete block design with three replications. PBZ was applied to shoot tips at concentrations of 10, 20, and 40 mg/L, at 7- and 14-day intervals, while distilled water was used for the control group. PBZ treatments significantly reduced plant height and internode length. The most notable reduction in plant height (20.3%) was observed with the 20 mg/L dose applied weekly. The highest marketable yield (184.03 t/ha) was achieved with the 40 mg/L PBZ treatment applied every 14 days, which was 1.08% higher than the control (182.07 t/ha). In contrast, the 20 mg/L weekly application resulted in an 11.7% decrease in yield. The average marketable fruit weight increased by 13.5% (reaching 98.44 g) under the 40 mg/L weekly treatment. However, this increase was accompanied by a 13.6% reduction in fruit number per plant. There was no significant relationship found between chlorophyll index (SPAD) and PBZ applications; however, the highest SPAD value (55.47) was measured in the 40 mg/L 7-day PBZ treatment. Fruit and leaf dry matter contents were not significantly affected. The PBZ doses and application methods used in the study did not leave detectable residues in cucumber fruits, and this finding demonstrates that the application is completely safe for food, representing one of the most critical outcomes of the study. In conclusion, foliar PBZ applications effectively suppressed vegetative growth. The 40 mg/L treatment applied biweekly offered an optimal balance between compact growth, fruit weight, and total yield, without compromising fruit quality. or leaving harmful residues.