GRAPE PESTS AND THEIR CONTROL 



205 



, Phylloxera. 



This minute sucking insect (Phylloxera vastatrix), injures 

 the grape by feeding on its roots. Decay usually follows its 

 work on the roots and is often more injurious than the harm 

 done directly by the parasite. This decay is always much 

 more serious on European vines than on those of our native 

 species. The phylloxera is a native of the United States east 

 of the Rocky Mountains, from whence it was introduced into 

 France and from France into California, where it causes much 

 greater damage than elsewhere in the United States. Wherever 

 the pest is found, it is more injurious in heavy than in sandy 

 soils. In fact, in very sandy soils the vines are often sufficiently 

 resistant to be prac- 

 tically immune. 



The life history of 

 the phylloxera is very 

 complex where the dif- 

 ferent forms of the in- 

 sect appear and need 

 not be entered into in 

 detail here. East of the 

 Rockies, the most evi- 

 dent indication of the 

 presence of the pest is 

 great numbers of leaf- 

 galls on the under side 

 of the leaves of the 

 grape as shown in Fig. 

 36. These galls, how- 

 ever, are seldom to be seen in California and are not present 

 on Concords and some other varieties in the East. The winter 

 egg may be taken as the beginning of the life cycle of the 

 phylloxera. From a single winter egg a colony may arise, the 



FIG. 36. Leaf ^galls of the phylloxera. 



