Abstract: 5-Substituted picolinic acid derivatives represented by the formula (I): ##STR1## wherein R.sub.1 represents a straight or branched chain halogen-substituted alkyl group having 2 to 6 carbon atoms or a substituted phenyl group having the formula ##STR2## wherein R.sub.3 and R.sub.4, which may be the same or different, each represents a hydrogen atom, a halogen atom, a lower alkyl group, a lower alkoxy group, a nitro group, an amino group, an N-alkyl-substituted amino group, an acylamino group, an acetyl group, an acyloxy group, a hydroxy group or a halogen-substituted alkyl group or R.sub.3 and R.sub.4, when taken together, represent a polymethylene chain; and R.sub.