DISEASES OF THE VINE. ] 573 



are of great economic importance, and a short review of 

 the principal diseases and pests is necessary to enable 

 the vine grower to recognize his enemies and to place 

 him in a position to combat them with .some measure of 

 success. There are also certain diseased conditions of the 

 vine which are not due to the aclion of parasites, but 

 may derive their origin from adverse conditions of the 

 soil or of the climate, and sometimes their real cause is 

 still obscure. 



NON-PARALITICAL DISEASES. 



Chlorosis or Yellows. This is characterized by the 

 yellowish aspect of the foliage and of the green parts of 

 the vine, with the formation of small, deformed, and 

 almost colourless leaves, which generally dry off in a few 

 days or weeks. Afterwards, small, thin and rachitic 

 shoots develop from the lower dormant buds on the 

 stem, often several arising together from the same bud 

 or point, and these soon share the same fate as the 

 foliage. This disease may be due to cold, or to exces- 

 sive or stagnant humidity in the soil, or it may be the 

 result of a serious disturbance of vital processes brought 

 about by parasitism. American vines, with the exception 

 of Vitis Berlandieri and to a certain extent also of V. 

 rupestris, planted in calcareous soils are particularly 

 subject to a very persistent form of chlorosis to which 

 they often succumb. Therefore American hybrids in- 

 tended for grafting stock, as well as American hybrid 

 ' 'direct producers", must have a satisfactory coefficient of 

 resistance against lime, otherwise they would be wholly 

 unsuitable for planting in the calcareous soils of these 

 Islands. Fortunately there are now many hybrids of 

 V. Berlandieri, V. rupestris, etc , which are able to 

 tolerate a soil with a high percentage of lime. Vines grow- 

 ing on moist calcareous soils are more easily affected by 

 chlorosis than those growing on dry or well drained soils. 



