1919.] PUBLIC DOCUMENT — No. 31. 23 a 



apparent diminution of the trouble as a result. Irish Cobblers 

 and Green Mountains were about equally affected by this 

 trouble, but the former, an earlier variety, usually succumbed 

 first. Dibble's Russet was noted as especially resistant to 

 drought conditions. 



The presence of the fungus Phoma in a large number of fields 

 throughout the State, the typical stem lesions caused by the 

 fungus, and the uniformity with which these appeared under 

 certain conditions, furnish strong evidence that this so-called 

 disease was responsible for a considerable amount of damage to 

 the potato crop last season. Laboratory tests, not yet com- 

 pleted, indicate that the fungus is at least mildly parasitic 

 under conditions of moisture. After examination of a few 

 fields in which Phoma was in evidence, it became apparent 

 that the injury from the fungus was practically limited to low- 

 lying areas, usually of rather heavy moisture-holding soil. 

 Where a field consisted of both high and low land there was 

 a gradual diminution of the trouble along the upward slope, 

 and often a merging into the trouble previously attributed to 

 drought. At a distance Phoma infected plants are yellow and 

 stunted in appearance. This condition is followed by wilting 

 and dying of the tops. Such plants invariably show conspicuous 

 brown lesions on the stem, and these often in combination form 

 a complete girdle. Typical Phoma pycnidia appear on the older 

 lesions. Pure cultures of the fungus were obtained from which 

 inoculation experiments are in progress. The present incom- 

 plete knowledge of this fungus makes impossible any definite 

 conclusions as to whether Phoma may be considered a serious 

 destructive parasite of the potato. However, preliminary 

 studies in the field and laboratory and careful observations 

 incline us strongly to the opinion that the Phoma disease of 

 potato will not, under normal seasonal conditions, prove of any 

 consequence. We believe the weather to be a prime contribut- 

 ing factor in the parasitism of the fungus, and that the disease 

 need not be considered in the general schedule of treatment 

 for diseases of this crop. 



Mosaic disease and leaf roll of potato were unusually preva- 

 lent and severe. Few fields of the Green Mountain type were 

 free from mosaic, and a rather careful survey indicates that 



