critical winter game ranges, Avoga webstevi is not believed to have serious, long-term 

 effects. The moth is subject to insect parasites and predators and does not completely 

 kill off sagebrush stands (Hall 1965). In time sagebrush naturally reinvades its old 

 sites which in the mean time have become more diverse plant communities. During drought 

 periods grasshoppers have been known to defoliate A. tridentata (E. F. Schlatterer, 

 letter 12/1/77). Galls of many kinds of flies (Diptera) are found on sagebrush (Hall 

 1965; Jones 1971; C. F. Tiernan, data on file at the Shrub Sciences Laboratory, Provo, 

 Utah). The effect of the galls is not known. Sagebrush hosts many other insects of 

 various orders. Some of these may protect the plant from disease vectors. Several 

 microbial-induced diseases are known (Krebill 1972). Some of these are widespread and 

 may be locally destructive; however, sagebrush populations are resilient and generally 

 are not significantly affected in the long run. D. L. Nelson (data on file at the Shrub 

 Sciences Laboratory, Provo, Utah) has recently isolated several fungal species of the 

 genera Vertioitl'iumi Fusari-uiVj and Rhi-zootonia from dying sagebrush in uniform gardens. 

 We have observed similar symptoms (dying desiccated plants) in natural populations. We 

 believe diseases induced by these fungi may be among the most serious sagebrush diseases. 

 Some microbes are likely useful for the vigor and growth of sagebrush. Wallace and 

 Romney (1972) found preliminary evidence that A. tvidentata formed symbiotic relation- 

 ships with microbial endophytes to fix atmospheric nitrogen. Williams and Aldon (1976) 

 found endomycorrhizae within A. tridentata roots and abundant spores around the roots. 

 Endomycorrhizae, in general, have a beneficial influence on plant growth by promoting 

 nutrient absorption through infected roots (Williams and Aldon 1976). For sagebrush, 

 the beneficial effect is suggestive but not yet proven. 



Use . --Artemisia tridentata is one of the more nutritious shrubs on western winter 

 livestock and game ranges. Subspecies tridentata has higher protein levels than the 

 other two subspecies (Welch and others 1977). Unfortunately, this species also contains 

 considerable aromatic oil, which may reduce its digestibility (Nagy and others 1964). 

 Nevertheless, because of its widespread abundance, its ability to grow with associated 

 grasses (figs. 4, 28), forbs, and other shrubs and its nutritious nature, big sagebrush 

 is the most important winter forage in foothill areas through much of the West for live- 

 stock and big game. Furthermore, the volatile oil content varies with subspecies and 

 accession (Sheehy and Winward 1976; Scholl and others 1977; Welch and McArthur, data 

 on file at the Shrub Sciences Laboratory, Provo, Utah) . Perhaps the oil content could 

 be reduced in improved planting stock. It is one of the best shrubs available for 

 use in revegetation of depleted winter game ranges in the Intermountain area (fig. 29) 

 (Plummer 1974) . 



29 



