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



Peridermium harhnessii may be recognized from the following 

 characteristics : Pycnia, if present, and aecia on well-defined spherical 

 to oblong, woody branch galls up to 8 cm. (rarely up to 30 cm.) in 

 diameter, and on trunk cankers that commonly originate from branch 

 galls adjacent to the trunk; small galls on 1- to 2-year-old twigs 

 frequently taking the form of a small pear ; aecia resembling irregular, 

 yellow, and usually confluent blisters 1-8 mm. wide and 1-3 mm. high, 

 rupturing laterally (circumscissile dehiscence), the peridial covers 

 falling away in large flakes soon after dehiscence ; filaments not abun- 

 dant, projecting from the dome and the floor of the aecium, frequently 

 continuous; aeciospores subglobose to obovoid and ellipsoid, 14—24 X 

 23-35/x; spore walls colorless and coarsely verrucose except for an 

 elongate, lateral smooth spot, 



Western gall rust is probably caused by a number of closely related 

 species or races of fungi, some requiring alternate hosts for survival 

 (see Hosts: Scrophulariaceae, below), some unable to infect alternate 

 hosts and transmitting the disease by aeciospores from pine to pine, 

 and some, as suggested by Meinecke, infecting both, alternate hosts and 

 pine, with aeciospores ("facultative heteroecism") . Races not needing 

 alternate hosts are a real danger to Old World hard pine forests. 



The spread of western gall rust can be stopped by thorough inspec- 

 tion of susceptible pines in the field and the annual removal of all 

 rust galls and cankers. The eradication of telial hosts (Scrophularia- 

 ceae, see below) in the vicinity of hard pines is of dubious value 

 for rust control unless their susceptibility to the particular race of 

 gall rust has been demonstrated. Systemic fungicides may become 

 useful for chemical control of gall rust. Since symptoms of gall rust 

 in pine may not appear for many years after infection has taken place, 

 the only practical safeguard against accidental introduction and inter- 

 continental spread of the disease is to prohibit entry of all living 2- 

 and 3-needle pines from North and South An ierica, except for experi- 

 mental use following rigorous inspection and retention in quarantine 

 for at least 4 years. 



Range: In North America it occurs along the Pacific coast from 

 Alaska to Mexico, eastward to the Atlantic coast from Nova Scotia 

 to New York. Also found in Central and South America. 

 Hosts: 

 Pinaceae — 



Indigenous in North America: 

 Pinus attemmta Lemm. 

 P. hanhsiana Lamb. 

 P. contort a Dougl. 

 P. coulteri D. Don 

 P. elliottii Engelm. var elliottii (as P. caribaea Morelet and 



P. heterophylla (Ell.) Sudw.) 

 P. engelmannii Carr. (as P. apacheca Lemm. and P. maynana 



Sudw.) 

 P. jeffreyi Grev. & Balf. 

 P. muricata D. Don 

 P. ponderosa Laws, var ponderosa 

 P. ponderosa Laws, var scopulorum Engelm. 

 P. radiata D. Don. 

 P. sabiniana Dougl. 



