Use of amide compound for promoting plant root growth

A root growth promoter comprising, as an active ingredient, a compound of formula (1):

• wherein R1 represents a C1-C6 alkyl group optionally substituted with (a) halogen atom(s);
• R2 represents a C1-C6 alkyl group optionally substituted with (a) halogen atom(s), a C3-C6 alkoxyalkyl group optionally substituted with (a) halogen atom(s), a C3-C6 alkenyl group optionally substituted with (a) halogen atom(s), or a C3-C6 alkynyl group optionally substituted with (a) halogen atom(s);
• R3 represents a halogen atom, or a C1-C6 alkyl group optionally substituted with (a) halogen atom(s);
• R4 represents a hydrogen atom, a halogen atom, a cyano group, or a C1-C6 alkyl group optionally substituted with (a) halogen atom(s);
• R5 represents a hydrogen atom, a halogen atom, a cyano group, a C1-C6 alkyl group optionally substituted with (a) halogen atom(s), a C1-C6 alkoxy group optionally substituted with (a) halogen atom(s), a C1-C6 alkylthio group optionally substituted with (a) halogen atom(s), a C1-C6 alkylsulfinyl group optionally substituted with (a) halogen atom(s), or a C1-C6 alkylsulfonyl group optionally substituted with (a) halogen atom(s);
• and R6 represents a halogen atom, or a C1-C6 alkyl group optionally substituted with (a) halogen atom(s).