New York Agricultural Experiment Station. 153 



the blight had made its appearance on a few leaves here and there all 

 through both fields. 



On September i, alternate strips of six rows in both fields were 

 very thoroughly sprayed with bordeaux mixture. As there was at 

 that time fully nine-tenths of the foliage in perfect condition it was 

 thought that the blight could surely be checked by spraying. How- 

 ever, such was not the case. By September 7 from two-thirds to 

 three-fourths of all the leaflets on the sprayed plants were more or 

 less affected and the unsprayed plants were but a trifle worse. A 

 week later the difference was a little greater, but at no time was it of 

 any importance. When the potatoes were dug it was found that in 

 one field the yield of the sprayed and unsprayed rows was the same ; 

 namely, at the rate of 63 bushels per acre. While in the other field 

 sprayed rows yielded 72 bushels per acre and the unsprayed ']2i- The 

 area of each field was about two-thirds of an acre, about one-half 

 being sprayed in each case. In this experiment spraying was a flat 

 failure. 



The explanation seems to be as follows : For a week preceding 

 the date of spraying the weather had been exceptionally favorable to 

 the spread of blight {PJiytoj;>]itJioya). Spores from the affected 

 leaves had been freely scattered over the healthy leaves, germinated 

 and pushed their germ tubes into the tissues of the leaves. Thus at 

 the time of spraying the fungus was already within the leaves out 

 of reach of the fungicide but had not yet made sufficient growth to 

 kill the tissue and cause the appearance of dead, brown spots. In 

 spite of the spraying the fungus continued to spread within the 

 leaves soon killing them. Had the spraying been made a week 

 earlier it is likely that the results would have been much more satis- 

 factory. 



As a rule, it isamsafe to postpone spraying until the appearance 

 of blight. Usually the blight becomes thoroughly established in a 

 field before it is observed. In any case it is necessary to act very 



