Effects of plastic mulch and paclobutrazol on bolting and yield of autumn sugar beet yield in Mashhad region

In this study, the effects of plastic mulch and paclobutrazol on bolting, yield and quality of autumn-sown sugar beet was studied in a split plot design based on randomized complete block design with four replications in Mashhad during two cropping seasons (2018-19 and 2019-20). Planting dates at three levels (10th, 20th and 30th of October) were allocated to main plots and bolting control at four levels (control, plastic mulch, paclobutrazol, and simultaneous application of paclobutrazol and plastic mulch) to subplots. The average reduction of bolting in plastic mulch, paclobutrazol, and simultaneous application of paclobutrazole and plastic mulch compared with control was 69.06, 32.98 and 91.88%, respectively. The treatments of plastic mulch, paclobutrazol, and simultaneous application of paclobutrazol and plastic mulch increased white sugar yield by 1.11, 1.93, and 1.19 t ha-1, respectively. There was no significant difference between different planting dates in terms of white sugar yield which could be due to the bolting occurrence in early planting and as a result reduction of sugar content and also the decrease in yield in late planting. In bolting control treatments, plastic mulch increased the yield by reducing about 70% of bolting on the second planting date compared with the first planting date. Results showed that the use of paclobutrazol and the simultaneous use of paclobutrazol and plastic mulch had a significant reduction in white sugar yield. On the other hand, due to the significant effect of the simultaneous application of paclobutrazol and plastic mulch on bolting reduction, it is necessary to conduct more studies regarding the amount and timing of paclobutrazol application to eliminate the negative effects on yield.