Brassicaceae seed meals produce ionic thiocyanate (SCN (-)), a bioherbicidal compound. This study determined the fate of SCN (-) in a field soil amended with seed meals of Sinapis alba, Brassica juncea, and Brassica napus and quantified crop phytotoxicity by monitoring carrot ( Daucus carota) emergence. Meals were applied at 1 or 2 t ha (-1), and soils were sampled to 35 cm for SCN (-). Maximum SCN (-) (211 micromol kg (-1) of soil) was measured at 5 days in 0-5 cm samples from plots amended with S. alba meal at 2 t ha (-1). Less than 30 micromol of SCN (-) kg (-1) of soil was measured at soil depths below 15 cm. At 44 days, SCN (-) was <15 micromol kg (-1) of soil in all treatments. Emergence inhibition of carrots seeded 15-36 days after meal amendment was found only in S. alba treatments. The rapid decrease of SCN (-) concentrations in Brassicaceae meal-amended soil indicates limited potential for off-site environmental impacts.

Control of green peach aphid (Myzus persicae), a globally important pest, using plant‐derived oils is a promising alternative to conventional insecticides. Although various plant‐derived oils are potentially useful for insect control, dose–response studies and efficacy comparisons among oils have not been widely reported. Our objective was to compare M. persicae control by plant‐derived oils, focusing on oils derived from Brassicaceae species that exhibit rotational and environmental quality benefits. We thus applied sprays of emulsified ethyl esters from the seed oils of yellow mustard (Sinapis alba), oriental mustard (Brassica juncea) and rapeseed (Brassica napus) to M. persicae in a laboratory bioassay. A dose–response relationship was modelled for the S. alba spray yielding LD50/LD95 values of 18.2 ± 0.87/128.1 ± 5.10 μg ester per cm2 (P < 0.0001). Ethyl esters of oils from all three species and soybean (Glycine max) ethyl ester were compared to determine the efficacy of Brassicaceae oils relative to the dominant plant‐oil spray currently available. All ethyl esters were equally efficacious despite measured differences in fatty acid profiles among the oils. Oils derived from mustards B. juncea and S. alba are potentially useful feedstocks for the production of insecticidal sprays, and testing on additional insects is warranted.