52 PROTECTION OF PLANTS, 1918-19 



give the same relative covering power on the leaf. Vigorous stirring while 

 pouring the dilute copper sulfate solution and lime milk together is necessary to 

 produce the maximum number of thin membranes and thus obtain the greatest 

 covering power. At the same time a mixture containing these small, thin 

 membranes will be easier to keep from rapid settling and thus make possible a 

 more even distribution of the membranes throughout the field. No amount of 

 agitating will yield good results when concentrated solutions are poured together.® 



The mixture is effective as soon as it has dried on the leaves. The copper in 

 the membranes is slowly dissolved when the leaves become wet. The lime 

 particles are also fungicidal. In making an application it is necessary to obtain 

 a uniform distribution of finely divided mist-like particles of the mixture on the 

 leaves. If the sprayer does not develop a high pressure the drops will be large. 

 The mixture will then run olif the leaves and the coating of colloidal membranes 

 will be uneven and much less efficient. The leaf need not be entirely covered by 

 the mixture, however, even under the best of conditions, for should a spore fall 

 on the leaf even at a distance of one-sixteenth of an inch away from a sprayed 

 area the germination of the spore is retarded. From what has been said one will 

 readily recognize how important the proper methods of mixing and applying the 

 solution are in determining its efficiency. 



All the well planned experiments have shown that while three sprayings will 

 often yield paying results, sometimes, however, they fail, due to the fact that they 

 were not applied at just the time required by the conditions of that season. 

 Therefore because of this showing, the advisability of spraying is often con- 

 demned or doubted. We have only to analyze the things accomplished with 

 from five to seven sprayings to understand why this practice is successful and 

 why a less number of sprayings may result in disappointment. 



The first application should be made when the plants are six to eight inches 

 high, or at least soon after this stage in their growth. While this application is 

 largely advised to carry the bug poison; the mixture has then an excellent chance 

 to coat the leaves which will soon be over-grown. Also this early application may 

 aid considerably in reducing the amount of primary infection. It is then necessary 

 to spray at least every two weeks thereafter until frost if the maximum benefits 

 are derived. This frequency of spraying is necessary because of the new growth 

 made by the vines after each application, and this in turn must be coated. The 

 older leaves, after the vines become dense, are not reached by the later sprayings, 

 but the coating they received probably remains effective the entire season. The 

 successive applications which keep the leaves coated with the colloidal membranes 

 and lime particles accomplish the increased yields in the following manner®: 



1. The spores of the early and late blight fungi, which are wind and insect 



