Six, 9, and 12-mm diam dicalcium phosphate tablets were evaluated for their release of acetochlor, metolachlor, and metribuzin. Greenhouse bioassays with Italian ryegrass demonstrated that herbicides from the smaller tablets did not control grass as long as from the larger tablets. Italian ryegrass was controlled within a 5- to 7-cm diam circle around the 12-mm diam tablet and a 5-cm diam circle around the 6-mm diam tablet. All tested herbicides responded in a similar fashion. Six-mm diam tablets released metolachlor for 11 weeks, while the 12-mm tablet was active for 28 weeks.