16 BULLETIN 903, IT. S. DEPARTMENT OF AGRICULTURE. 



phylloxera and the actual death of the vine. The following points 

 have important bearing on this : 



Soil conditions and drainage. — From a survey made throughout 

 the different districts of California, the following general statements 

 can be made in regard to the destruction of vineyards when the vines 

 are 8 to 10 years of age or older before becoming infested : 



Vines live longer in rich, deep, well-drained soils. Under such 

 conditions, vineyards known to have been infested for 20 years and 

 longer still bear crops, have only a .few vines actually dead, and 

 but a small percentage bearing little or no crop. 



Vines die sooner and the crop of the vineyard is more rapidly 

 diminished in quantity and quality when established on rich soil 

 only a few feet deep and with poor drainage, or on side-hill soils 

 lacking moisture. 



Vines are still more rapidly affected in heavy soils, more or less 

 shallow, with compact clay subsoil. In such types of soil, the vines, 

 more or less stunted and enfeebled, may live a number of years. 

 After a winter of unusually heavy rainfall they may show a very 

 rapid serious decline or even a majority of them may die within a 

 year. 



Vines growing in a well- drained, very loose, and friable sandy soil, 

 or one with a surface of blow sand several inches in depth, seem to 

 be almost immune to the attack of phylloxera. 



As a sandy soil becomes heavier in texture and of poorer drainage, 

 so the vine succumbs more readily to the attack of the insect. 



Age of vine at infestation. — Young vines are destroyed more readily 

 during the first three years, before they have established a fairly 

 good root system. When vines are 8 or 10 years old the quality and 

 texture of the soil become main factors, and the more or less rapid de- 

 struction of the vineyard depends on the adaptation of the vine to 

 the soil and the advantages of prolification and diffusion for the 

 insect. The general experience has been as follows: 



Cuttings infested in their early growth rarely survive the first 

 year. 



Rooted vines, infested from the time of planting, produce from the 

 start a very poor vineyard, which rarely lasts more than three or four 

 years, the individual infested vines living after infestation hardly 

 more than two years. If vines become infested during the second 

 or third year from planting, they may last longer if they have 

 a good root system, and in this case the vineyard may produce one 

 or two crops smaller than normal and perhaps last five or six years. 

 When a vine is three years old or more before infestation, its longev- 

 ity depends somewhat on variety, much more on age, and especially 

 on soil conditions. 



