8 BULLETIN 903, IT. g. DEPARTMENT OF AGRICULTURE. 



Infestation from accidental distributing centers may be avoided 

 by strictly enforced quarantine measures. 



Accidental spread has been the main cause of most of the phyllox- 

 era infestation throughout the vineyards of California because of 

 its being an initial inoculation, developing later into a center of 

 natural dissemination. 



A general survey of the growth of the grape industry, which 

 at times, as in the late eighties and early nineties, attained the 

 proportion of a boom, furnishes an indication of the accidental 

 spread which took place concurrently. 



Cuttings were used almost exclusively for planting vineyards in 

 preference to rooted vines, the latter being used for replanting 

 " misses," and even then not commonly used. As will be shown 

 later, there is little, if any, danger in disseminating the phylloxera 

 from cuttings, unless these are heeled in in infested soil while await- 

 ing shipment. It is for this reason that the accidental diffusion 

 was greatly restricted. If rooted vines had been commonly used, 

 originating from the same district as the cuttings, the accidental 

 diffusion would have been so general as perhaps to have precluded 

 before long the growing of vinifera vines on their own roots. 



THE WINGED MIGRANT NOT A FACTOR IN SPREAD UNDER CALIFORNIA 



CONDITIONS. 



Profiting by the investigations and experiments that were being 

 carried on in France, the University of California in conjunction 

 with the State Board of Viticulture made extensive efforts to ar- 

 rest the ravages of the phylloxera, and made investigations pertain- 

 ing to its life history and habits. These deserve special mention 

 in this report. 



Dr. F. W. Morse (16) of Oakland, Calif., during the period 

 1881-1886, as an assistant in the General Agricultural Laboratory, 

 discovered in the course of his investigations on August 26, 1884, 

 specimens of the gall louse or leaf-inhabiting form of the phylloxera. 

 As is noted under the heading " The gallicole and its relation to 

 California conditions 1 ' (p. 95), this is the only recorded instance 

 of the finding in California of the leaf galls. In this connection it 

 may be said that in the experimental vine3 7 ards of the Bureau of 

 Plant Industry, United States Department of Agriculture, in which 

 are collected many varieties and hybrids of species of American 

 vines, not a few of which are susceptible to leaf galls when culti- 

 vated in the Eastern or Middle States, an exceptionally good field 

 for observation is offered. Mr. G. C. Husmann, under whose direc- 

 tion these vineyards are conducted, states that the leaf gall, to his 

 knowledge, has never been found in them. Extensive correspondence 



