Measurement of phytotoxicity of commercial and unformulated soil‐applied herbicides

Summary The relative potencies of analytical‐grade lenacil (99% ai) and its commercial formulation, Venzar® (80% ai), technical‐grade ethofumesate (96%) and its commercial formulation Nortron® (21% ai) were evaluated using oats (Avena sativa L. cv. Selma) as test plant. In all experiments the dose‐response curves of the pure herbicide and its commercial product were parallel. The average potency of Venzar relative to lenacil, assayed twice in a sandy loam, was 0⋅80 and thus equal to the expected 0⋅80. The average potency of Nortron relative to ethofumesate, assayed in a sandy loam and a loamy sand, was 0⋅25 and close to the expected value of 0⋅21. The implication of using the technique of parallel‐line assay in herbicide studies is discussed and its potential use in other contexts than the present one is suggested.