Selectivity of Soil Herbicides on Vigour and Physiological Responses of Grafted Cuttings of Ryahovo

Between 2018 and 2021, at the IASS “Obraztsov Chiflik” experimental vine nursery – Ruse, trials were conducted to investigate the effect of pendimethalin (alone and in combination with clomazone) on the vegetative and physiological parameters of grafted vine cuttings. The study was carried out on leached chernozem using the table-grape cultivar Ryahovo grafted onto rootstock SO4 (Berlandieri × Riparia), and compared with an untreated control. Results show that pendimethalin applied alone or combined with clomazone had no statistically significant effect on the percentage of cuttings which sprouted, with values remaining from 92.5 to 96.3%. A slight suppression of shoot length was observed with the combined treatment, whereas pendimethalin alone did not produce meaningful deviations from the control. Analysis of growth rate indicates that the primary significant factor with proven influence was the year (climatic conditions), whereas the herbicides and their interaction were not statistically significant. Chlorophyll and carotenoid contents remained stable under pendimethalin treatment, which indicates lack of adverse effect on the photosynthetic apparatus. The pendimethalin + clomazone combination produced a mild to moderate phytotoxic effect manifested as a chlorotic halo on the first emerged leaves of the cuttings; this symptom resolved later and did not affect further development. The tested soil herbicides exhibited high selectivity towards grafted vine cuttings and can be determined as safe at the doses used and under the conditions. Climatic factors had a dominant influence on growth dynamics, while herbicide treatment did not cause substantial physiological disturbances.