REPORT OF THE SOCIETY 71 



significant that plants from seed of diseased vines always suffer more severely 

 than plants from seed of health}^ vines. 



Control 



Spraying with Bordeaux 4-4-50 is effective in controlling hopperburn pro- 

 vided that the underside of the leaves is sprayed thoroughly. This is obvious 

 when considering the fact that nymphs feed on the underside of leaves as above 

 noted. 



(b) Mosaic and Mosaic Dwarf. 



W. A. Orton first described Mosaic as a disease of potatoes from observ- 

 ations he made in potato fields at Giessen while visiting in Germany, although 

 Quanjer believes that the disease has been known for a long time in Europe. 

 Orton on his return fcund the disease to be quite prevalent in Maine in the 

 Green Mountain variety. This was in 1912 and since that time the disease 

 has been found in practicall}' every potato-growing area of the United States 

 and Canada. 



The cause of the disease is not yet determined, although it is certainly a sys- 

 temic disease, and it has been placed here in Group 1 because of the established 

 fact that aphids are agents of inoculation. 



While the disease may be regarded as new, as compared with Late Blight 

 for instance, it is highly infectious and has spread with alarming rapiditj'. In 

 1919 careful estimates made in Aroostook County, Maine, of 40 fields of Green 

 Mountain and the same number of Bliss Triumph showed an average of 28 per 

 cent of infected hills of Green Mountain and 46 per cent in the case of Bliss 

 Triumph. In some cases the diseased plants amounted to 100 per cent. It is 

 therefore of paramount importance that efforts be continualh' made to check 

 the spread of this insidious disease. The difficulty involved hes in the fact that 

 the potato tuber, a vegetative part of the plant, is used for seed purposes and 

 the causal principle may be present in the tubers as a result of late infection 

 without there being distinct signs of the disease in the foliage. 



Symptoms of the Disease 



The disease maj^ manifest itself in either of two ways according to the 

 variety or according to the locality. The typical symptom from which the name 

 arose is the mottling of the foliage. Lighter green areas occiu- in the leaves and 

 these lighter green areas may be few cr numerous, they may be very small or 

 reach the size of a quarter of an inch, and in shape are usually angular. The 

 leaflets may also be more or less ruffled or wrinkled owing to the modified growth,, 

 and where this is the case the wrinkles are likely to obscure the mottling at first 



