REPORT OF THE SOCIETY 53 



borne, are killed by contact with the colloidal membranes giving off free copper, 

 or by the alkaline solution derived from the lime particles. 



2. The germination of the spores is inhibited or retarded when they, lie 

 close to either the colloidal membranes or lime particles. 



3. Tip-burn is prevented to a large extent in a manner that is not fully 

 understood. 



4. Flea beetles are repelled and the number of punctures reduced. 



5. The plants live out a normal indeterminate growth until killed by frost. 

 This period of lengthened growth often reaches two weeks, and results in a larger 

 number of first class tubers. 



The next most important factor influencing the efficiency of spraying is the 

 time of application with reference to rain periods; this is especially important at 

 the stage in the development of the potato when late blight causes its heaviest 

 losses. Since new outbreaks of blight can be correlated definitely with rain 

 periods of the proper character, spraying should be done before such rain periods, 

 if it is possible to predict their arrival. This insures that all the new growth up 

 until the rain period is covered. Infection which would be accomplished during 

 the rain period is thus prevented to a large extent. 



Even after there is little danger of late blight killing the tops in time to 

 reduce the yield, it is advisable to continue the spraying, since heavy tuber 

 infections may follow relatively unimportant late foliage infections. 



The advantages of spraying are so apparent, and the procedure so easy of 

 successful application, that it is unfortunate that growers of small acreage find 

 themselves hampered in many ways from adopting the practice. It is because 

 of this fact that I want to outline a simple scheme of cooperation which will 

 largely avoid the objections of the small grower, and at the same time probably 

 more efficiently accomplish the best results. 



The most important reason why small growers do not spray are, first that the 

 investment in machinery and materials is prohibitory and, second, that the amount 

 of labour involved throughout the season seriously interferes with the necessary 

 care that other crops demand. It is with a view to removing these difficulties, 

 which must be overcome to extend potato spraying, that the following plan is 

 suggested. This method may be called community or cooperative spraying: 



A single efficient potato sprayer will take care of 100 or more acres of potatoes 

 according to weather conditions. In regions where each grower raises ten 

 acres or less a single machine will thus serve for several fields and reduce the 

 investment. 



By simply passing the machine from one grower to another, many difficulties 



