170 EXPERIMENT STATION. [Jan. 



age in Massachusetts; and in order to prevent attacks from 

 this, farmers should commence to spray when the potatoes 

 are not more than one-fourth grown, which would ordinarily 

 be about the 20tli of June. Much of the injury to potatoes 

 is due to the flea beetle, which affects them in a manner sim- 

 ilar to the early blight. 



We believe that a first spraying of potatoes should be made 

 with Bordeaux and '' Disparene," instead of Paris green, 

 since " Disparene " is a reliable insecticide, while Paris green 

 is not, at the present time. 



Copper Sulfate Treatment of Stagnant Water. 



In a previous report we gave the results of a copper sulfate 

 treatment of the college pond.^ This pond is located on the 

 college grounds, and contains about 8,000,000 gallons of 

 water; it is quite shallow and has a muddy bottom. The 

 amount of water which it receives during the summer months 

 is not sufficient to cause a very constant overflow, and partly 

 for this reason it occasionally becomes stagnant. There is 

 also some pollution from cesspools which drain into it, and 

 during freshets considerable amounts of fine sand, silt and 

 clay are carried into tlie pond. Much of this silt, etc., re- 

 mains in suspension for a long time, giving the water a yellow- 

 ish tinge and roily appearance. Evaporation tests show that 

 the water contains 45.6 parts sediment to 10,000 parts of 

 water. During June the water usually has a disagreeable 

 odor and becomes quite obnoxious. This odor is similar to 

 that which rises from frog ponds where considerable decom- 

 position takes place, and at other times it has the odor which 

 is characterized as " fishy." 



The pond has frequently been drained, which is responsible 

 for stimulating growths of algse, particularly Spirogyra, and 

 for the past few years Anabsena has been present in greater 

 or less amounts. It should be stated at the outset that our 

 object in treating the pond was not to clear up points of 

 controversy in connection with the copper sulfate method of 

 treatment ; it was done largely to obviate a nuisance. 



That copper sulfate has an effect upon alga3 has been known 



1 Eighteenth annual report, Hatch Experiment Station, 1906, pages 143-146. 



