626 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



to the use of lime in their potato fields by these growers, and in part 

 to climatic conditions specially favorable to scab. In respect to 

 yield and market quality this variety continued to be very satisfac- 

 tory. This difficulty with potato scab serves to illustrate the fact 

 that it is not yet possible to safeguard all our potato-growing sec- 

 tions against the introduction and spread of wart by the use of 

 immune varieties without placing a severe burden on the growers 

 in certain sections for which well-adapted immune sorts have not 

 been determined. The release of the " safety zone " from the re- 

 quirement of immune planting has resulted in an extensive return 

 to the growing of the highly wart-susceptible Kusset-Rural variety. 

 Special measures are being taken by the State department of agri- 

 culture to insure thorough inspection at digging time of all such 

 plantings. This experiment, if it may be so called, should at least 

 give additional and positive information regarding the distribution 

 of the disease, if any, beyond the old determined areas of infestation. 



In Maryland the furnishing of an approved immune variety of 

 potato for planting in infested gardens was undertaken by the State, 

 with the result that all the known infested gardens in which potatoes 

 were grown this year were planted to a pure stock of Irish Cobblers. 



As a result of the exi^erience that has been acquired and the studies 

 that have been made on potato wart since its discovery in Pennsyl- 

 vania five years ago, it is the belief of the specialists that American 

 potato culture is not seriously threatened by the disease. It is their 

 belief that if the growth of immune varieties can be enforced for 

 a period of years, as now seems possible under State quarantines, 

 there is reasonable hope of entirely eliminating potato wart from 

 this country within no great period of years and at no great cost 

 either to the States concerned or to the growers in areas under 

 quarantine. It is still highly important that accurate information 

 as to the distribution of the disease, particularly as regards its ap- 

 pearance in new areas, be secured, and the strict use of only immune 

 potatoes in all infested gardens must be enforced. 



Investigational work complete and published, or nearing com- 

 pletion, affords a sound basis for determining the future attitude 

 which the Department of Agriculture may take toward this disease. 

 The conditions of infection and the factors operative in dispersal and 

 elimination of the parasite have been worked out to reasonable com- 

 pleteness. The application of soil sterilization to the problem of wart 

 extermination has been investigated and new information has been 

 secured regarding the use of heat and chemicals for this purpose. 

 There remain several scientific questions of importance and great 

 interest which will receive further attention in the Bureau of Plant 

 Industry. 



WHITE PINE BLISTER RUST QUARANTINES. 



Following up the quarantine of certain counties of Washington 

 lying west of the summit of the Cascade Mountains, promulgated 

 March 15, 1922, on account of the discovery by agents of the Depart- 

 ment of Agriculture of several blister-rust infestatione, principally 

 on black currants, in the Puget Sound region of Washington, it be- 

 came necessary in March of this year to extend this quarantine to 

 cover the entire State. This action followed an amendment to the 



