Both Younger (1958) and Snow (1959) have noted that the pond- 

 weeds (Potamogetons) , are somewhat resistant to this chemical in 

 rates up to 2.5 p. p.m. Another disadvantage is that fish in 

 treated ponds occasionally may be rendered unpalatable for some 

 time after treatment. It should not be used in irrigation systems. 



On the credit side, Silvex under 5.0 p. p.m. is not hazardous 

 as a poison to humans, livestock or fish. 



Granular 2,4-D and Silvex 



Granular or pelletized 2,4-D and Silvex have been found effective 

 for control of parrots feather, water lilies, watershield, bladder- 

 wort, etc., when applied at rates of 20 to 40 pounds acid equivalent 

 per acre. The rate of 150 to 200 pounds of 20 per cent 2,4-D 

 granules has been found to be effective but slow acting, sometimes 

 requiring as much as 4 to 6 weeks to clear an area. Prolonged residual 

 effects may follow. Truchelut and Williams (1960) have observed 

 that pH of the water affects the success of 2,4-D applications which 

 are more successful under acid conditions. Lack of consistent results 

 with pelletized 2,4-D may be due in part to this ecological factor. 



Sodium Arsenite 



Sodium arsenite is a cheap and very effective chemical for 

 control of nearly all species of submersed aquatic plants. During 

 the warm summer months, 4.0 parts per million will kill even very 

 dense growths in both hard and soft waters . Where the vegetation 

 is not dense, 2.5 parts per million will provide adequate control. 

 If the vegetation is dense, a sudden and complete kill of vegeta- 

 tion should be avoided, particularly if the pond does not have a 

 fresh supply of water which can be turned in to meet the oxygen 

 demand of decaying vegetation. 



In the control of weeds along the shorelines of large lakes, 

 where there is the maximum of diffusion, up to 10 p. p.m. are re- 

 quired for successful treatment. In the treatment of fish ponds, 

 sodium arsenite has a wide margin of safety in its toxicity to 

 fish. About 11 to 12 parts per million are required to kill fish. 



In fish ponds, in midsummer, the critical period for fish occurs 

 about 3 days after treatment, when the plants which have fallen to 

 the bottom, begin to decay rapidly. The decomposition uses up 

 oxygen which is also necessary to maintain fish life. In ponds with 

 supply pipes, a moderate amount of fresh water can be turned in, 

 if necessary. In ponds without an inflow, it is recommended that 

 not more than one-half of the total area of the pond be treated at 

 one time. The congregation of fish at the surface or along the 

 shoreline is an early sign of oxygen depletion. 



A standby pump of 200 gallons per minute or more capacity can 

 be used for emergency purposes in aerating water where there is no 

 inflow. 



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