Aromatic solvents at 100 to 150 p. p.m. applied during a 15 -minute period 

 have satisfactorily controlled filamentous green algae in western irrigation 

 canals. 



In Reservoirs and Large Canals Carrying Water for Potable or Industrial 

 Uses or for Irrigation 



For control of algae or rooted submersed aquatic species in slowly moving 

 w^ater: Copper sulfate applied continuously in sufficient quantity to maintain 

 0.6 to 1.0 p. p.m. concentration in the water throughout the growing season 

 for aquatic w^eeds. The concentration should be maintained at 1.0 p. p.m. 

 early in the season. It may be reduced gradually after midsummer to as 

 low as 0.6 p. p.m. late in the growing season. These treatment rates give 

 adequate control and are well below the maximum concentration of 3.0 p. p.m. 

 of copper ion or 7.5 p. p.m. of copper sulfate in potable water supplies, as 

 established by the U. S. Public Health Service. 



In Ponds and Lakes 



(1) For control of rooted submersed species in still water: Sodium arsenite 

 at 3 to 4 p. p.m. will give adequate control usually for all, or most, of one 

 grow^ing season. For treating localized areas along the shoreline of a lake, 

 concentrations of 6 to 10 p. p.m. may be necessary for adequate control 

 because of diffusion into untreated areas. 



Comments and precautions . --Arsenical compounds are recognized poisons 

 and must be handled with extreme care to avoid injury or death to hunnan 

 beings, livestock, or ganne animals. Wash application equipment and empty 

 containers thoroughly with water after each use. Wear goggles during 

 spray application and wash hands thoroughly afterw^ard. Delay use of 

 treated water for bathing, swimming, lawns, gardens, or animals for 3 

 days. Do not use the arsenical treatment in any waters intended for use 

 in rice culture. Carefully observe all State laws on applications of arseni- 

 cals. 



Fish are not killed by concentrations of sodium arsenite below 1 1 to 

 12 p. p.m., which are in excess of the concentrations recommended for 

 aquatic w^eed control. 



(2) For control of rooted species (such as parrotfeather, waterweed, coon- 

 tail, pondweeds, and naiad): Dichlone at 10 to 20 pounds per surface acre. 

 At these rates, concentrations of the chemical in treated water range from 

 2.7 p.p.m. to 10.8 p. p.m. in w^ater 5 to 10 feet deep. Toxicity of dichlone to 

 fish has been variable and safe concentrations have not been definitely 

 determined. 



(3) For control of blue -green algae: Dichlone at 1 pound per surface acre 

 of water has given effective control without injury to higher aquatic life, 

 fish, or zooplankton. Repeated applications usually are necessary to main- 

 tain control. 



(4) For control of filamentous green algae: Copper sulfate at 0.5 to 1.0 

 p.p.m. 



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