40 



bloom forms before the plants start to grow. The bloom 

 must be heavy enough to shade out the rooted plants and 

 should be maintained throughout the season. A bloom 

 thick enough so that the bottom cannot be seen at the 

 depth of 1 foot is heavy enough for this purpose. The 

 pond will have tobe watched closely, as there is danger 

 that the bloom may become heavy enough to cause an 

 oxygen depletion during warm nights. This method has 

 the advantage of producing fish food while controlling 

 the weeds. 



In some ponds fertilization may not control the 

 weeds and hand cutting will be necessary. In shallow 

 ponds a scythe will be the most satisfactory tool, but 

 in deep ponds one of the mechanical weed cutters is 

 necessary. When possible, the vegetation should be 

 raked up on the banks to prevent an oxygen depletion 

 when it decomposes. 



Weeds can be killed by solutions of copper sulphate 

 and sodium arsenite that are too weak to kill the fish, 

 but this method should be used only as a last resort 

 because either of the chemicals will kill most of the 

 minnow food organisms. These chemicals should not be 

 used without the supervision of a trained biologist. 



Two or three hundred carp placed in a small pond 

 during the winter will eliminate all the weeds. This 

 procedure is prohibited by law in most States and 

 cannot be undertaken without special permission because 

 of the danger of introducing carp in forbidden waters. 

 A new chemical (Butyl Ester of 2, 4-Dichloro- 

 phenoxy Acetic Acid, usually called 2,4-D) has been 

 effective in killing emergent vegetation. The chemical 

 2,4-D is sold under various trade names as a dandelion 

 killer. For use on aquatic vegetation a solution of 1 

 part of 14 percent active ingredient 2,4-D to 130 parts 

 of water is used. One part of Vatsol (a wetting agent) 

 should be added to each 2,000 parts of solution to 

 reduce the surface tension and thus increase the wetting, 

 power of the solution. The chemical 2,4-D is applied to 

 the plants underpressure from a hand-operated sprayer. 

 The spray should be applied from a suitable distance so 

 that the solution will adhere to the leaves. The plant 

 will die even though its entire surface is not covered. 

 The plant may turn yellow 24 hours after the application 

 of 2,4-D but will not be completely dead for a week or 

 two depending on the species of plant and the weather. 

 New shoots and seedlings will come up later, and for 

 complete control these must be killed too. The chemical 



