A METHOD FOR DETERMINING THE FUNGICIDAL 



COEFFICIENT OF LIME SULPHUR AND OTHER 



COMMON FUNGICIDES. 



BY HARRY C. YOUNG AND E. H. COOPER. 

 INTRODUCTION. 



The physiological effect produced upon fungous spores by the great 

 number of substances used at present or in the past as fungicides, has 

 been made the basis of a wide series of investigations. These studies 

 have naturally divided themselves and have been conducted along two 

 distinct lines. 



The first of this work taken up aimed at determining in the laboratory 

 the exact action of various fungicides upon the germination of fungus 

 spores. It was conceded that the effectiveness of fungicides depended 

 upon their ability to either prevent spore germination altogether, or to 

 cause the death of the young mycelium after its appearance. Exposure 

 of spores to solution of various types and strengths was the fundamental 

 factor in work of this kind. 



Attention was first turned to laboratory methods which as near as 

 possible, approximated field conditions. An attempt of this nature was 

 made by Blodgett, Wallace and Hesler (10) in 191L The laboratory 

 tests carried out by them are in brief as follows. They worked in the 

 main with lime sulphur solutions. Slides were sprayed with the fungi- 

 cidal mixture and then were exposed to the air until the coating had 

 dried thoroughly. A few drops of water containing viable spores of the 

 fungus were put on the slide. Only one side of this slide was sprayed 

 the other side being left as a check. The slides were then placed in a 

 moist chamber long enough for the spores to germinate. The microscope 

 was then used for determining the comparative fungicidal values of the 

 various mixtures. These tests are supposed to represent as nearly as 

 possible exact field conditions. No definite values can be placed on 

 fungicides in terms of a standard by this method, as the process of 

 drying would cause various chemical changes, thereby strengthening or 

 weakening their fungicidal properties. However the plan gives better 

 results than could be had by field tests as in the latter too many factors 

 enter in. 



19th Mich. Acad. Sci. Rept., 1917. 



