104 U.S. DEPT. OF AGRICULTURE MISC. PUB. 939 



cause any swelling of the wood, small cankers frequently diamond- 

 shaped; aecia resembling irregular, yellow, and usually confluent 

 blisters approximately 2 mm. wide and high, rupturing irregu- 

 larly at the apex, the peridial covers soon falling away after de- 

 hiscence; filaments projecting from the dome and the floor of the 

 aecium, rarely continuous; aeciospores subglobose to irregularly 

 ellipsoid, 11-22 X 16-37/x, greatly varying in size and shape; spore 

 walls colorless and moderately verrucose except for an elongate, 

 lateral smooth spot. 



Stalactiform rust may be mistaken for other stem rusts of pine that 

 resemble it, particularly since aecia rarely develop on old cankers. In- 

 fected trees are frequently gnawed by rodents, causing severe resinosis 

 and annual ridges at the margins of cankers. 



Successful control depends largely on early recognition, particularly 

 the recognition of large cankers on mature trees as being caused by this 

 rust. As in white pine blister rust ( Cronartium ribicola J. C. Fischer) , 

 long-distance spread can be avoided by repeated pruning of cankered 

 branches and by prompt removal of trees with stem infections. New 

 infection of pine can at least be minimized by the eradication of telial 

 hosts in the immediate vicinity of susceptible pines. Systemic fungi- 

 cides may be developed for efficient chemical control in the future. 

 Since stalactiform rust may remain dormant and unrecognizable in 

 pine for many years after infection, the only practical safeguard 

 against accidental introduction and intercontinental spread of this 

 dangerous disease is to prohibit entry of all living 2- and 3-needle 

 pines from North America, except for experimental use following 

 rigorous inspection and retention in quarantine for at least 4 years. 



Range : In North America it is largely confined to the Pacific coast 



and Rocky Mountain regions from British Columbia to Idaho, but 



is found as far east as Manitoba and Minnesota, and believed to 



be transcontinental. 

 Hosts : 

 Pinaceae — 



Pinus banksiana Lamb. 



P. contorta Dougl. 



P. jeffreyi Grev. & Balf . 



P. ponderosa Laws. 

 Scrophulariaceae. Confirmed by infection with aeciospores. — 



Castilleja angustifolia Nutt. 



C. applegatei Fern. 



C.coccinea (L.) Spreng. 



G. rhexifolia Rydb. 



Melampyrum lineare Desr. 

 Probable additional suscepts. — Species of Orthocarpus, Pedicularis, 



and Rhinanthus. 

 Literature : 



Arthur, J. C. Manual of the rusts in United States and Canada. 



Purdue Res. Found., Lafayette, Ind., U.S.A. 1934. 

 Mielke, J. L. The rust fungus (Cronartium stalactiforme) in lodge- 

 pole pine. Jour. Forestry 54 : 518-521. 1956. 

 Wagener, W. W. Infection tests with two rusts of Jeffrey pine. 



Plant Dis. Rptr. 42 : 888-892. 1958. 





