Copper sulfate is still most economically, safely, and widely 

 used as an algicide. In situations where the nuisance algae do not 

 respond well to treatments, Dichlone and Hyamine 2389 may be used 

 although their margins of safety in toxicity to fish appear to be 

 small. The latter chemical is effective in killing those swimming 

 pool, raceway, or pond species of algae or diatoms unaffected by 

 chlorine or copper sulfate. Dichlone killed common blue-green 

 algae at rates as low as 30 parts per billion, but the algae came 

 back as is their habit because they are spore formers and because 

 the plant nutrients responsible for their growth in the first place 

 were still there. 



No chemical will be perfect in all situations because the 

 problem is biological, involving many ecological factors. Copper 

 sulfate is an example. Where one part per million may destroy the 

 heavy scums of Hydrodictyon in hard water at one pond station, three 

 to five treatments at 0.3 p. p.m. will prove safest in soft water at 

 another . 



Fertilization to stimulate phytoplankton growths which shade 

 out the coarse weeds is the most efficient method of weed control 

 and promotes increased biological productivity. Moyle (1949) showed 

 that Aphanizomenon apparently built up resistance in some way to 

 copper sulfate treatments over a period of 26 years of treatment in 

 the Fairmont lakes of Minnesota. In 1921, the species was controlled 

 with dosages between 0.15 to 0.25 p. p.m. In the period 1943-46, 

 0.5 to 0.8 p. p.m., or more than double the amount was required. 



Much progress has been made, particularly in the treatment of 

 emergent and f loating-leaf ed aquatics. The search continues for the 

 perfect algicide and submersed weedicide. Definite and rapid 

 progress is being made and more extensive field testing may show 

 that they are actually at hand. 



Appendix A lists many of the effective herbicides used in 

 aquatic weed control work today, together with the quantities 

 recommended for control of nuisance plants. 



American lotus or yonkapin 



33 



