Thinning is one of the most tedious and exhaustive operations in row-crop plant cultivation. It is mostly done manually by employing many labours during hot days in summer. In this study, a pneumatic mechanism was developed to automatically root up the redundant plants to provide enough space for the remaining sugar beet plants. The algorithm designed for thinning the sugar beet plants when there is significant overlapping between the adjacent plants. Retaining the single plants untouched was regarded in the algorithm not to diminish the overall yield of the field due to bare spaces. The performance of the machine was investigated at three different levels of forward speeds. Results showed that the best accuracy of the machine in providing the desired thinning distance between the remaining crops was gained at the speed of 2 and 3.5 km/hr. The machine also achieved well in leaving the single plants untouched with an accuracy of 99.1% while the speed did not have a significant influence on this achievement. Both laboratory and field experiments showed a reasonable performance which encourages the use of automatic thinning for sugar beet cultivation.