algaecidal activity of some substituted 1,3-diphenylureas, 1-phenyl-3-(2-pyridyl)ureas and the corresponding thioureas

Twelve ureas and thioureas with 1,3‐diphenyl‐ and 1‐phenyl‐3‐(2‐pyridyl) were tested as potential herbicides in a simple screen against two species of algae Chlorella fusca and Anabaena variabilis. Several were shown to inhibit growth at 100 mg litre−1 but only 1‐[2,4‐bis(azidosulphonyl)phenyl]‐3‐(2‐pyridyl)urea and 1,3‐bis(4‐isopropyl‐ idenehydrazinosulphonylphenyl)thiourea showed any activity at 1 mg litre−1. This compares with the well‐established urea herbicide diuron which, in identical tests, gives similar inhibition of growth at concentrations as low as 0.01 mg litre−1.