Effect of plant growth regulator used with adjuvants in winter wheat (Triticum aestivum L.)

Crop yields depend not only on genetic traits, agronomic practices, and weather but also on effective crop protection. European agriculture aims to reduce the use of harmful chemicals while maintaining yields. Studies show that adjuvants can reduce the required doses of plant protection products. While their role in herbicide and fungicide applications is well documented, research on plant growth regulators remains limited. Field trials were con-ducted at the Institute of Plant Protection – National Research Institute in Poland to evalu-ate the impact of reduced doses of growth regulators, along with adjuvants, on the growth and yield of winter wheat. The study aimed to evaluate the potential and effectiveness of combining the plant growth regulators mepiquat chloride and prohexadione calcium with various adjuvants and additives in winter wheat under field conditions. The experimental treatments included a mixture of mepiquat chloride with prohexadione calcium (Medax Top 350 SC) applied together with citric acid; fertilizers such as urea and ammonium sulfate; and adjuvants—including heptamethyltrisiloxane-modified polyalkylene oxide (Slippa), 76% paraffin oil (Atpolan 80 EC), 80% rapeseed oil fatty acid methyl esters, sur-face-active agents (surfactants), and a pH buffer (Atpolan BIO 80 EC), as well as ammo-nium sulfate ((NH₄)₂SO₄ – 40%), a cationic surfactant (20%), and triethanolamine (5%) (AS 500 SL). The studies showed that it is possible to achieve the same results using half the standard doses of regulators, combined with adjuvants, as when using full doses. This also applied to plant height as well as qualitative and quantitative grain parameters. Additional-ly, the findings demonstrated that the effect of mepiquat chloride combined with prohexa-dione calcium and adjuvants varied depending on weather conditions during crop growth.