Isothiazole and pyrazole derivatives for use as plant growth regulators

Use of a compound of formula (I)

• wherein
• X is S, N or NR5 and Y is N or NR5, with the proviso that one, but not both, of X or Y is N;
• R1 and R3 are, independently, hydrogen, or optionally substituted alkyl, alkenyl, alkynyl, heterocyclyl, trialkylsilyl, arylalkyl, aryloxyalkyl, arylthioalkyl, aryl or heteroaryl;
• R2 is optionally substituted alkyl, alkenyl, alkynyl, heterocyclyl, arylalkyl, aryl or heteroaryl;
• R4 is H or acyl;
• R5 is hydrogen or optionally substituted alkyl, alkenyl, alkynyl, heterocyclyl, trialkylsilyl, arylalkyl, aryloxyalkyl, arylthioalkyl, aryl or heteroaryl;
• or a salt or N-oxide thereof;
• as a plant growth regulator.