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Title: Survival, frost susceptibility, growth, and disease resistance of corkbark and subalpine fir grown for landscape and Christmas trees

item Barney, Danny
item BAUER, MICHAEL - University Of Idaho
item JENSEN, JENNIFER - University Of Idaho

Submitted to: HortTechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/13/2013
Publication Date: 4/1/2013
Citation: Barney, D.L., Bauer, M., Jensen, J. 2013. Survival, frost susceptibility, growth, and disease resistance of corkbark and subalpine fir grown for landscape and Christmas trees. HortTechnology. 23:194-200.

Interpretive Summary: Corkbark fir (Abies lasiocarpa var. arizonica) and subalpine fir (Abies lasiocarpa. var lasiocarpa) trees produced from seed collected in the Desert Southwest of the United States were grown in northern Idaho and northeastern Oregon to test those seed sources for their potential as Christmas trees and ornamental landscape nursery stock. Both variety and seed sources influenced the growth rates of the trees. On average, corkbark fir trees grew faster than did subalpine trees and were taller as early as two years from seed. For the six corkbark fir seed sources evaluated, heights after nine years in the field averaged 2.08-2.89 m. For the 10 subalpine seed sources evaluated, heights averaged 1.31-2.27 m. Across the three planting sites, corkbark fir survival ranged from 43% to 96% and subalpine fir survival ranged from 63% to 99%. Both corkbark and subalpine trees broke dormancy and developed new shoots very early in spring and were susceptible to frost damage. On two sites, frost damage was typically minor and had little impact on the trees' appearance. On another site, frost damage was more severe. A Phoma-type fungal pathogen became a serious problem at one planting site in northern Idaho. On average, subalpine trees were more susceptible to the pathogen than were corkbark trees and seed source in subalpine fir influenced susceptibility. Of the five fastest-growing subalpine fir provenances, four proved highly susceptible to the disease. Corkbark fir trees were more resistant to the pathogen than subalpine fir and seed source did not significantly influence disease resistance. Fungicide programs using Pageant or Pageant plus Bravo Weather-Stik proved highly effective in controlling the disease in corkbark and subalpine fir. Corkbark fir seed sources from the Apache-Sitgreaves, Coconino, and Gila National Forests appeared suitable for Christmas tree production, although fungicides may necessary on some sites in some years. For Christmas tree growers willing to invest in fungicide programs, subalpine fir seed sources from the Cibola, Dixie, Kaibab, and Uncompahgre National Forests showed some promise. In areas where the fungal blight is present, seedlings from the seed sources tested in these trials may prove blight susceptible and landscape use may be unacceptably risky. Neither crop is recommended on sites with frequent or severe spring frosts. Within both crops, we observed trees with growth rates, forms, and disease tolerance or resistance suitable for Christmas tree and landscape use on suitable planting sites. Twenty-three corkbark and eight subalpine trees were transplanted to a commercial nursery for further testing as potential cultivars for landscape use.

Technical Abstract: Trees from six corkbark fir (Abies lasiocarpa var. arizonica) and 10 subalpine fir (A. lasiocarpa var. lasiocarpa) seed sources were grown at the University of Idaho Sandpoint Research and Extension Center (SREC) and two commercial nurseries in Idaho and Oregon. Post transplant mortality was highest during the first two years. After six growing seasons, survival averaged 76% and 80% for corkbark and subalpine fir, respectively. In SREC irrigated plots, survival averaged 96% and 99%, respectively. Spring frost damage occurred annually on 66% to 100% of trees during 2002-2006. In SREC plots, damage was minor and did not adversely affect appearance. Neither crop is recommended for sites subject to frequent or severe spring frosts. Tree heights and growth rates varied significantly between seed sources. In general, corkbark fir grew faster than subalpine fir. After nine years in the field, SREC mean corkbark tree heights ranged from 2.08 m (Santa Fe National Forest (N.F.)) to 2.89 m (Apache-Sitgreaves N.F.). Subalpine fir mean heights ranged from 1.31 m (San Isabel N.F.) to 2.27 m (Kaibab N.F.). 2006 tree heights at the commercial nurseries averaged 24% and 36% less for corkbark and 24% and 55% less for subalpine fir, respectively, than for corresponding SREC trees. Corkbark fir proved moderately resistant to resistant to a Phoma-type fungal blight. Three corkbark seed sources appeared suitable for Christmas tree production. The use of seedlings for landscapes may be unacceptably risky due to disease potential. Subalpine trees were more susceptible to the putative Phoma blight, but some provenances may still be suitable for Christmas tree production. Some trees within both varieties proved resistant to or highly tolerant of the blight. Two fungicide programs (Pageant or Pageant plus Bravo Weather Stik) controlled the blight. Eight subalpine fir and 23 corkbark fir at the SREC were selected for further testing as possible cultivars.