POTATO DISEASES AND THEIR REMEDIES. 1 5 



As a result of this conflict of tendencies in the plant there 

 occurs a critical period during which the continued health of the 

 plant, if not its very life, hangs in the balance. 



Whether this explanation is correct or not, the fact is certain 

 that the fortnight including and immediately following the blos- 

 soming period is the turning point, the crisis in the life of the 

 potato plant. 



The production of a profitable crop depends more upon its 

 protection at this period than at any other during its growth. 

 Before this time it will quickly recover from very severe rav- 

 ages of insects ; a little later it will do the same ; but serious in- 

 jury to the foliage or arrest of development from unfavorable 

 soil conditions at this period will start the plant upon a decline 

 which is disastrous to the crop of tubers and leads to the prema- 

 ture death of the plant ; and, in our experience, no subsequent 

 treatment makes amends for neglect at this time. If, however, 

 the plant is carried in full vigor through this critical period it 

 starts upon what is virtually a new lease of life, a vegetative 

 period which, with the more vigorous varieties in our northern 

 climate seems to have no natural terminus. The length of the 

 subsequent period of vegetative development seems dependent 

 not on internal factors primarily, but on external conditions, 

 chiefly climatic, which have so varied at Burlington during 

 recent years as to bring successive crops of the same variety and 

 on the same soil to so-called maturity at dates varying from 

 September 25 to November lo. It is during this second or veg- 

 etative period that all of the marketable crop is developed. It 

 is for this that we have grown the plant, and it is important, 

 therefore, to inquire more exactly when and at what rate this 

 development occurs. In order so to trace the relative rate of 

 growth of the crop, we have during three seasons at the Ver- 

 mont station made a series of partial diggings at ten-day inter- 

 vals from the blossoming period through to full maturity with 

 vigorous varieties, carefully cared for and sprayed. This has 

 covered a period of about seven weeks, and has revealed the 

 miportant fact that there is fully as great a rate of growth dur- 

 ing the last half as during the first half of this seven-week 

 period. The following results of one such season's digging is 

 typical of them all. 



