88 Vermont Agricut,tttral Report 



hangs in the balance. If once carried safely past this critical 

 period and well started toward tuber formation, with foliage 

 healthy and abundant, its life may be prolonged for many weeks, 

 indeed almost indefinitely ; but if during this critical period the 

 plant is seriously weakened by insects, fungi, or other agencies, 

 so as to start it upon a decline, it seldom fully recovers. More 

 usually under these conditions it succumbs to the enervating 

 process of tuber formation and soon dies. 



The practical importance of this condition is apparent when 

 it is understood that the entire crop qf salable tubers is formed 

 after this critical period is past, and that the full success of the 

 crop depends upon retaining the healthy foliage for from one to 

 three months after the blossoming period. 



The following figures showing the time and rate of develop- 

 ment of the potato tuber, were secured at the Vermont station 

 by digging successive plots at intervals of ten days, beginning at 

 the close of the blossoming season, the plants being preserved 

 in healthy condition by spraying: 



YIELD OF TUBERS AT DIFFERENT DATES. WHITE STAR POTATOES, 



PLANTED MAY 20. 



Yield of 

 Date of Total Yield marketable Average size 



Digging per acre size of tubers 



In the majority of potato fields in this State the plants are all 

 dead by the last week of August, yet in the case cited above, 

 which fairly represents average conditions, fully one-half of the 

 marketable crop was formed after that date. The importance of 

 maintaining the perfect health of the potato foliage during the 

 last few weeks of its possible development is much underesti- 

 mated. 



The potato requires more water than do most plants ; in- 

 deed, the production of a full crop demands that fully one-fourth 

 of all the water that falls on the soil during the entire season 

 shall be absorbed by the plant and either retained or passed off 

 through its leaves. Moreover the time of most active demand 

 for this water is at and shortly following the critical period. 



