Vebmont Agricultueal Report 89 



The securing of this water supply is dependent upon three 

 thing's ; first, the water containing character of the soil,, deter- 

 mined by humus content and thorough pulverization; second, 

 surface tillage to conserve this; third, healthy foliage to carry 

 on transpiration which is the pumping process in plants. Much 

 of the so-called "blight" of potato leaves is really the physio- 

 logical disease "tip-burn" due to insufficient attention to one or 

 all of these factors. 



Starch manufacture is scarcely second to water supply in 

 importance for tuber formation ; this occurs entirely in the green 

 leaves under the invigorating influence of sunlight. The extent 

 of healthy leaf surface is therefore an exact index to the capacity 

 for starch formation. When it is remembered that one-half of the 

 possible crop is formed after the third week in August the im- 

 portance of the preservation of the healthy foliage through the 

 early autumn becomes apparent. The average potato grower 

 has no just conception of his dependence upon this late foliage 

 for a full crop. 



As evidence of this we are frequently asked whether by 

 spraying or otherwise protecting the foliage we may not unduly 

 stimulate the potato to "run to tops." In one case in our vicinity 

 a man who had sprayed and thus secured a fine stand of healthy 

 plants wrote and asked if he should not go over them with a 

 roller to break them down and check their growth. Another was 

 advised by his neighbor that he was ruining his crop and must 

 cut the rank tops back. This was about the middle of August. 

 He appealed to us for advice. Wishing to secure experimental 

 data we offered to pay him for possible loss if he would cut 

 back the tops by one-half in alternate rows in his field and report 

 the outcome to the Experiment Station. He did so and secured 

 a yield of 152 pounds per row where so top pruned as compared 

 with 221 pounds where allowed to grow. 



The result is the same whether the tops are cut off with a 

 sickle as in this case or destroyed by blight or insects as so com- 

 monly occurs in August, where the plants are not protected by 

 spraying. One season when the blight struck our field about the 

 middle of August we had a gain of over 200 bushels per acre 

 due simply to prolongation of the life of the leaves in this way. 

 We have in previous reports of this Board and in Experiment 

 Station bulletins discussed the advantages and methods of spray- 

 ing. Suffice it here to repeat that as a result of trials extending 

 now through fifteen consecutive years at the Vermont Station we 

 have found the Bordeaux-arsenic-mixture to be an almost perfect 

 "cure-all" for the diseases and insects attacking the potato. The 

 following summarizes our experiments in spraying late potatoes. 



