60 MISC. PUBLICATION 273, U.S. DEPT. OF AGRICULTURE 







Figure 24. — Enlarged buds, or gout disease, of grand fir caused by the 

 balsam woolly aphid (Chermes piceae) . 



main trunk it galls the bark and covers it with a dirty-white 

 encrustation. On terminals it causes a swelling to form around 

 the buds, leaving them in a depression and making the twigs ap- 

 pear to end in solid knobs, hence the name of "gout disease of fir." 

 Infestations, if heavy, weaken trees, cause a thinning of foliage 

 in the lower crown, progressing toward the top and finally killing 

 the tree. Wherever spraying of tall trees is economically feasible, 

 this aphid can be controlled with a 6-percent miscible-oil spray. 



The hemlock chermes (Chermes tsugae (Annand)) (fig. 25) 

 appears as a white, cottony encrustation on the bark and as white 

 tufts on the needles of western hemlock in California, Oregon, 

 Washington, and British Columbia. It seriously weakens and kills 

 trees, particularly ornamentals in the Pacific Northwest. 



