WIND-BLOWN RAIN, A FACTOR IN DISEASE 

 DISSEMINATION 



By R. C. Faulwetter, 



Associate Botanist and Plant Pathologist, South Carolina Agricultural Experiment 



Station 



INTRODUCTION 



In an earlier article ^ the author presented data from field experiments 

 which lead to the conclusion that the spread of that disease was due to 

 the combined action of wind and rain. It was also shown that the 

 spread of similar diseases of plants affecting the leaves, flowers, fruits, 

 and twigs, caused by motile bacteria had not been satisfactorily ex- 

 plained by investigators, while nothing in the literature on the subject 

 precluded the possibility of such an explanation applying equally as 

 well in these cases. Numerous statements appear which permit a very 

 general application of this explanation. 



The film of water over the surface of the afiected leaves caused by 

 dew contains viable bacteria which emanate from the lesions, as was 

 demonstrated by several experiments, and it was held to be reasonable 

 that this condition would exist during rains. The spread of such a 

 suspension of bacteria by the combined action of wind and rain most 

 plausibly explained the dissemination of the disease noted in the field. 



Experiments have been conducted with the object of analyzing this 

 agency of disease dissemination, and, so far as the results of laboratory 

 tests permit application to natural and field conditions, added support 

 to the earlier conclusions has been the result. The method and the 

 results of these experiments in which the influence of size of drops, 

 distance of fall, depth of surface film, elevation and inclination of sur- 

 face film, and motion of the air upon the distance of splash have been 

 studied are presented here, together with a consideration of the impor- 

 tance of this agency of disease dissemination, which is justified by the 



newer information. 



METHOD AND APPARATUS 



Several drawn-glass droppers of different diameter were made and 

 fitted separately to a burette having a glass stopcock. The diameters 

 were such as permitted drops of 0.02, 0.04, 0.06, and o.i c. c. in volume 

 to fall. Such surfaces as dry glass plates, dry blotting papers, wet glass 

 plates, saturated blotting papers, and water i cm. deep in a petri dish 

 were used and in this way the results of the fall upon a dry impervious 

 surface, a dry porous surface, a very thin film of water (such as would 



' Faulwetter, R. C. dissemination of the angular leafspot of cotton. In Jour. Agr. Research, 

 V. 8, nc. 12, 457-475, 2 fig. 1917. Literature cited, p. 473-475. 



Journal of Agricultural Research, Vol. X, No. 12 



Washington, D. C. Sept. 17, 1917 



jw Key No. S. C— 2 



(639) 



