Within this large territory, centers of infection by limb rust have been observed in most of the National 

 Forests where there are ponderosa or Jeffrey pines, but distribution of the disease is not continuous. In- 

 fection centers have been observed as follows: In the Black Hills and Medicine Bow National Forests in 

 Wyoming; in the Roosevelt, Arapaho, Pike, San Isabel, Rio Grande, San Juan, and Uncompahgre National 

 Forests and Rocky Mountain National Park in Colorado; in the Ashley, Fishlake, Manti-LaSal (both parts), 

 and Dixie (all divisions) National Forests and Bryce Canyon National Park in Utah; in all 12 National Forests 

 and on both rims of Grand Canyon National Park in New Mexico and Arizona; in ponderosa pine stands of 

 the Charleston Division and in Jeffrey pine stands of the Mono Division of the Toiyabe National Forest in 

 Nevada; in Jeffrey pine stands in the Plumas National Forest and the 11 National Forests south of it as well 

 as in Kings Canyon and Sequoia National Parks in California; and in the Parque National Sierra de San Pedro 

 Martir in Baja California. 



Although there are several other rusts of pine trunks and branches in eastern North America, Europe, 

 and Asia, limb rust has not been reported in these regions. 



REPORTED DAMAGE 



Concern expressed by forest managers in southern Colorado prompted Hedgcock's studies and early 

 reports of limb rust (7, 8). He found the disease to be abundant, long- established, and destructive in the 

 San Juan National Forest. Garrett's observations in 1920 (5) revealed a destructive outbreak of long 

 standing in what is now Bryce Canyon National Park. 



Subsequent records did not reflect serious concern by land managers about limb rust until W. Drew 

 Chick made a survey at Bryce Canyon in 1935, as reported by Mielke (11). Chick concluded that limb rust 

 and dwarf mistletoe were causing the most serious damage to ponderosa pine in the Park. One speculation 

 in his file report is of particular interest: "If rust and the Black Hills beetle should work in association 

 (there is little present indication in the stand), the results are likely to reach disastrous proportions." 



During the 1940's, forest managers began to seek advice regarding limb rust problems in Arizona, 

 New Mexico, and the Dixie National Forest in Utah: prime mature and large overmature pines were being 

 lost to the disease. In response, Mielke summarized available information on linxb rust in a report 

 distributed in 1944 to National Forests in the Southwest. He recommended that rust infection be considered 

 a major factor in selection of trees for harvest. He pointed out that a drastic job of selective cutting would 

 be needed on the Powell (now included in the Dixie) National Forest because the number of infected mature 

 trees was so large. Management guidelines for this Forest at that time called for a 50-year cutting cycle, 

 which was too long an internal if infected trees were to be salvaged without serious losses. Mielke later 

 reported that about 11 percent of pines 3.6 inches d.b.h. or larger were infected by limb rust in one area 

 on this Forest and that the percentages were much higher in selected plots (11). Damage was concentrated 

 in trees 12 inches d.b.h. and larger. 



In the Southwest generally, where infection levels are lower than those on the Dixie, the prospect of 

 losses from limb rust didn't appear too serious. In the supposedly hard-hit Apache National Forest, F. G. 

 Hawksworth in 1951 found that symptoms like those of limb rust were probably related to drought and 

 insects rather than to rust; rust trees occurred at the low rate of five or fewer per hundred acres (17). 

 Infection at this level or at the higher levels found in some districts could be handled almost without loss 

 by the "improvement selection system" combined with short (not over 20-year) cutting intervals that had 

 been recommended by Pearson (12). 



In the Sierra Nevada, the limb rust problem became apparent on the Inyo National Forest in 1948. 

 Wagener provided information the following year that was used as a basis for a program of salvage logging 

 for infected Jeffrey pines By this means, as in ponderosa pine stands in the Southwest, incidence of limb 

 rust has been steadily reduced in managed stands . Additional centers of heavy infection are being found , 

 but the percentage of trees infected appears low over broad areas (4, and author's reconnaissance). 



Memorandum to Inyo Forest Supervisor dated June 3, 1949. 



5 



