GRAPE-VINE P^VLLOXERA 



159 



upon them also. Some at this time develop into winged females, 

 which escape from the soil and fly to neighboring vines and lay 

 eggs which hatch into males and females. This is the only sexual 

 generation in the whole life cycle. 



Injury. This is a serious pest of the grape, as above intimated. 

 The galls on the roots are frequently accompanied by a rotting of 

 the plant tissue. It is not so destructive, by any means, in America 

 as in Europe. Most varieties of grapes grown here are resistant, 

 yet in California it is regarded as an important pest of the grape. 



Control. The general recommendations are to use resistant 

 vines. There is a marked variation in the resistance of different 





ft 



FIG. 176. The grape-vine phylloxera, leaf form. (Alter Marlatt, U. S. Bu. Ent.) 



species and varieties. Not all varieties can be used as stock 

 for desired scions. As is well known, the wild grape of America 

 makes good stock for roots. 



On deep loose soils carbon bisulfid may be used against the 

 root form, but not on clay nor on dry, rocky hillsides. This treat- 

 ment is hardly practical and has met with only indifferent success. 

 Treatment with carbon bisulfid is rather expensive, costing from 

 $15 to $25 per acre. It is applied by pouring one-half to three- 

 fourths of an ounce of the liquid into holes a foot deep. The holes 

 are made from eighteen to twenty-four inches apart, and not nearer 

 than one foot to the vine. 



