New York Agricultural Experiment Station. 159 



is caused by spores which fall upon the ground and are washed down 

 to the tubers by the rain. In some cases the fungus may pass down 

 the stem and the tubers become infected in that way ; but this method 

 is the exception rather than the rule. 



So far as known, the potato blight fungus has no spores which 

 live over winter. It is believed that the fungus survives the winter 

 in slightly affected tubers. Hence it is advisable to avoid planting 

 tubers which show any signs of disease. 



The philosophy of spraying as a preventive of blight and rot in 

 potatoes is this: — The leaves are coated with a substance (bordeaux 

 mixture) which either prevents the germination of the spores or 

 else kills their delicate germ tubes before they can penetrate the leaf 

 tissue. Consequently, the fungus is unable to establish itself in the 

 leaves and there are no spores to fall upon the ground and cause 

 rot. 



CONCERNING THE USE OF POISON WITH BORDEAUX 

 MIXTURE IN SPRAYING POTATOES. 



In Bulletin 221 the writers advised against the use of paris green 

 alone for " bugs," and recommended the use of bordeaux mixture 

 containing paris green whenever it is necessary to fight insects. The 

 experience of the past season tends to confirm us in this opinion. 

 The extra expense of using bordeaux with the poison is slight and 

 the benefits are likely to be considerable. (See Bulletin 221, pages 

 261-262.) In the Fleet experiment (Page 150) the expense of ap- 

 plying " Green Arsenoid " with a Leggett powder gun was 49 cents 

 per acre for each application, while in the Jagger experiment (Page 

 134) the expense of applying bordeaux and paris green was only 98 

 cents per acre for each application. About the same quantity of 

 poison per acre (two pounds) was used in both cases and the " Green 

 Arsenoid " cost 43^ cents per pound less than the paris green. 

 Hence, the actual extra expense of using the bordeaux was only 40 



