Thidiazuron (TDZ) Thidiazuron plant cell culture (defoliation), also known as defoliation, defoliation urea, first used as a cotton defoliation agent, is the active ingredient of Dropp®. Cytokinin activity was later found in bean. TDZ is a derivative of N,N’ -diphenyl urea (DPU) and belongs to the substituted phenylurea family of compounds that exhibit similar cytokinin activity to adenosine-based cytokinin compounds.