This investigation studied simazine (2-chloro-4,6-bis(ethylamino)-s-triazine), atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine), propazine (2-chloro-4,6-bis(isopropylamino)-s-triazine), and prometone (2-methoxy-4,6-bis(isopropylamino)-s-triazine). Preemergence applications of granular formulations of simazine on attaclay or calcium sulfate of simazine at 1 to 2 ppmw controlled Potamogeton, Najas, Ceratophyllum, Heteranthera and Zannichellia. Higher rates were required to control filamentous algae (Cladophora and Pithophora) and chara (Chara vulgaris). Early postemergence applications of wettable powder to submersed aquatics and filamentous algae were often effective. Atrazine gave similar results. Concentrations of 0.5 to 1.0 were effective in controlling Cladophora and Pithophora and three species of Potamogeton in pond applications. Spray applications, generally, were more effective than broadcasting granular atrazine. Propazine and prometone did not control submersed species in concentrations up to 3 ppmw.

Simazine had a relatively high margin of safety with respect to acute toxicity to fish. It was less toxic than propazine, prometone or atrazine. Granular forms were less toxic than wettable powder or emulsifiable concentrates. Laboratory tests on bottom organisms gave an acute LD50 toxic dosage of 28 ppmw. Field observations did not demonstrate a serious reduction in the production of bottom organisms. However, the control of aquatic vegetation brought about ecological changes affecting bottom dwelling and weed clinging organisms. These changes would affect certain fishes with special food habits.