AbstractA chemical hybridizing agent (CHA: WL 84811, azetidine‐carboxylic acid. Shell Chemical) was applied to annual ryegrass (Lolium rigidumGaud. cv. Wimmera) at four levels: 0, 1·6, 2·4 and 3·2 kg active ingredient (a.i.) ha−1, at booting and at anthesis with a view to reducing seed set and increasing the proportion of cell solubles in the senescing and dead plants. The CHA treatments reduced stem elongation by up to 40% and reduced the proportion of pollinated florets progressively according to the concentration of CHA. At 3·2 kg (a.i.) ha−1only 14% of florets were fertilized compared with 86% on the zero (control) treatment.The CHA treatments also resulted in progressive increases in the number of secondary tillers. Since there was no increase in the amount of neutral‐detergent solubles associated with increased CHA application, it was concluded that storage carbohydrates, which might otherwise have been directed towards seed development, were partitioned towards increased tillering. There was no effect, therefore, on the proportion of neutral‐detergent soluble material in senescing an