Effects of adjuvants on the effectiveness and rainfastness of rimsulfuron in potato

Adjuvants are used with herbicides to increase their efficacy. In this study, it was demonstrated that the application of 0.1% of the non-ionic surfactant (NIS, Contact) and 0.5 L ha⁻¹ of a crop oil concentrate (COC, Renol) did not improve the efficacy of rimsulfuron on Amaranthus retroflexus. In contrast, the same treatments enhanced performance and rainfastnes of rimsulfuron in Chenopodium album. Increasing non-ionic surfactant concentration to 1 L ha⁻¹ increased rimsulfuron performance around 10-fold for A. retroflexus compared to around 3-fold for C. album. The same treatment reduced 12-fold the rainfastness of rimsulfuron on A. retroflexus while improving 2-fold the rainfastness of rimsulfuron on C. album. Measured ED₅₀ and ED₉₀ doses of rimsulfuron indicated that the addition of the 0.2 L ha⁻¹ of NIS improved the recommended (60 g a.i. ha_-1) and the reduced (30 g a.i. ha⁻¹) dose effect of rimsulfurom in potato crop in the field. The highest potato yield was recorded (60 tons per ha) when 60 g ai. ha⁻¹ of rimsulfuron was applied at three growth stages [leaf development (S1) + vegetatively propagated organs (S4) + development of tuber (S7)] of the crop without using a NIS; not significant differences were measured when the same dose of rimsulfuron was applied at the three (S1, S4, and S7) and two (S1, S4) growth stages with NIS.