80 BULLETIN" 951;, U. S. DEPARTMENT OF AGEICULTURE. 



Fungi which parasitize Cronartium ribicola are not imcommon. 

 Their use in artificial inoculation of infections on pines has been 

 attempted (172, 173, 174), but with little success. There appears 

 to be little prospect for success commensurate with the expense 

 involved. 



The separation of the pines from the Ribes plants is the most 

 efficient method of controlling the disease in a given locality. To 

 judge from the frequency of this recommendation for combating 

 the disease in European literature, apparently considerable work of 

 this kind has been done in Europe; but no definite statement of 

 results in specific instances have been found. 



The use of screens of another species of tree between Ribes and 

 Pinus strobus has been recommended in Europe (131, p. 41). No 

 one has stated the results of such treatment in any given instance, 

 however. 



There must be a chance to secure much valuable data on the 

 success or failure of various methods of treatment which have been 

 tested in Europe, but which have never been published. This can 

 only be done by making definite investigations in Europe from the 

 American standpoint. It must be remembered that from the 

 European point of view the white pine is an introduced and com- 

 paratively unimportant tree. Its diseases, therefore, are not made 

 the subject of systematic and prolonged study. Many facts of value 

 fundamental to the control of this disease in America can only be 

 determined by the intimate study on the ground of the much older 

 infections of Europe. 



Experiments in Control in North America. 



In all control of parasitic plant diseases the fundamental thing is 

 to determine the extent and the distribution of the disease to be 

 controlled. The parasitic fungi are so generally distributed by the 

 wind and are so insidious in their spread that they usually have 

 gotten well started before their presence is discovered. Newly dis- 

 covered imported diseases must be attacked at once or not at ail, 

 if eradication is to be accomplished, but more attention should be 

 given to the matter of determining reliably the extent of outbreaks 

 of such diseases. Scouting is a very important part of any disease 

 eradication or control campaign. A well-conducted, intensive, 

 plant-disease survey will do much to aid in determining the status 

 of a new disease. 



METHODS USED. 



The control of white-pine blister rust has been attempted in 

 North America (1) by means of quarantines of the host plants, 

 (2) by the eradication of advance infections, (3) by the separation 



of the two hosts, (4) by sanitation, (5) by screening Ribes or pines 



