The Effect of Adjuvants on the Location of Herbicide Deposits on Wild Oats

320Studies were initiated to assess whether the addition of selected adjuvants alter the location of herbicide deposits on plants, and to determine if any such changes could be correlated with biological effect. The postemergent grass-killing herbicides, diclofop-methyl as Hoegrass containing 375 g of active ingredient (a.i.) per liter (at rates of 0.05 to 1.6 1 ha ⁻¹) and flamprop-methyl as Mataven containing 375 g a.i. I⁻¹ (at rates of 1.0 to 16.0 1 ha ⁻¹) were applied with and without a nonionic surfactant and an emulsifiable oil to wild oat (Avena fatua L.). A fluorometric technique used to measure spray retention showed that with diclofop-methyl, retention by the top and middle of the plant was similar but lower than that of the basal part of the plant. With flamprop-methyl, retention by the top of the plant was higher than that of the middle, which in turn retained more than the basal area of the plant. While the addition of adjuvant decreased the amount of diclofop-methyl retained on the basal area and increased the amount retained on the top of the plant, with flamprop-methyl, it did not make any appreciable change. Diclofop-methyl potency was improved by 10 to 15% with a nonionic surfactant and by 40 to 50% with an emulsifiable oil. With flamprop-methyl, the addition of adjuvant had a nonsignificant variable effect. The results confirm other work indicating that there is no correlation between total spray retention and efficacy. Furthermore, they show that the location of the spray retention is different for the two herbicides evaluated.