formulations of Bordeaux have been used, some with partial control 

 as mentioned previously. 



Control work in the past has not been entirely confined to spray- 

 ing. Many European investigators advocated legislation to prohibit 

 the importation of Douglas-fir nursery trees, in an effort to exclude 

 R. pseudotsugae from established plantations (11, 60, 62). 



Some of the earliest control recommendations were based on 

 felling of diseased trees during autumn and winter and burning 

 infected branches before spring (27, 42). Geyr (19) maintained that 

 the best method was by developing resistant or immune varieties. 

 As this view became accepted many reports of varietal differences in 

 resistance were published (6, 31, 35, 36, 39, 44, 46, 47, 54, 73). 



The selection of resistant trees on warm dry sites has been advo- 

 cated by Merkle (34) for the control of Adelopus needle cast disease, 

 and might well apply for the control of R. pseudotsugae. Wide 

 divergences in relative resistance of the various strains of Douglas-fir 

 to the disease are readily seen in the plantations of the Northeast 

 (Fig. 22). The intermingling of branches of healthy and diseased 

 trees has been continually observed throughout the duration of this 

 study. It seems apparent that selection of individuals for needle 

 cast resistance, with coordinate programs of propagation, whether 

 by means of cuttings, grafts, or both, will be necessary if Douglas-fir 

 is to be grown successfully in the region. Of interest here is the 

 increasing concern shown, by Douglas-fir plantation managers in 

 the Pacific Northwest, toward the dual threat posed by severe and 

 continuing outbreaks of R. pseudotsugae and A. gaumanni in their 

 natural and original locale. Such a combined menace in the natural 

 range of the Douglas-fir adds an imperativeness to the question of 

 selection for disease resistance not presented by even the most favor- 

 able economic inducements in the Northeast and Europe. 



56 



