Pesticide interaction creates hybrid residue.

When applied in combination, the herbicides N-(3,4-dichlorophenyl)-propionamide (propanil) and N-(3-chloro-4-methylphenyl)-2-methyl-pentanamide (solan) were transformed in soil to an unexpected residue-asymmetric 3,3',4-trichloro-4'-methylazobenzene. Each herbicide contributed one-half of the asymmetric azobenzene molecule.