Necessity, legality and safety of the plant growth regulators applied in viticulture

The plant growth regulators (PGRs) are widely used in Chinese viticulture, with a substantial number of registered products; however, the applied necessity and safety remain subject of ongoing debate. This study first examines the alignment between the regulation needs in grape production and currently registered products to demonstrate the necessity and legal basis for using PGRs in viticulture. It then evaluates the safety of PGR-treated grapes from the perspectives of maximum residue limit (MRL) regulations, actual residue levels, and dietary risk, and further compares the registration status and MRL standards for commonly used PGRs on grapes between China and other countries. The main findings are as follows: Firstly, PGRs are indispensable in modern viticulture. The usage of registered products is legal, which basically matches the Chinese viticulture needs in terms of active ingredients and key regulatory points. However, the registration information lacks the specificity of cultivars and cultivation modes compared to frameworks in Japan and the USA. Secondly, the domestic MRLs have already covered the commonly used active ingredients used in viticulture, such as cyanamide, forchlorfenuron, thidiazuron, and S-abscisic acid, but the overall coverage remains notably inadequate relative to the range of currently registered PGRs. In addition, the domestic and international MRLs for forchlorfenuron and thidiazuron on grapes exhibited significant discrepancies. Thirdly, the residues and dietary exposure risks of PGRs from grapes were all at relatively low levels, indicating that grape consumption is safe from a food safety standpoint. Based on these findings, the authors propose several recommendations to improve the application and regulatory system of PGR used in viticulture, including establishing a differentiated pesticide registration mechanism targeting specific cultivars and cultivation models, synchronising the residue standard with the pesticide registration, promoting standardized cultivation practices, and enhancing routine science communication and public outreach. These measures aim to provide a scientific foundation for the rational use of PGRs on grapes and inform future revisions of registration policies and MRL standards.