VIEW ARTICLE

Ecology and Epidemiology

Epidemiology of Pitch Canker Disease in a Loblolly Pine Seed Orchard in North Carolina. E. G. Kuhlman, Principal plant pathologist, U.S. Department of Agriculture, Forest Service, Southeastern Forest Experiment Station, Research Triangle Park, NC 27709; S. D. Dianis(2), and T. K. Smith(3). (2)(3)Southern nursery operations manager and assistant western seed manager, respectively, Weyerhaeuser Company, Hot Springs, AR 71901 and Tacoma, WA 98477. Phytopathology 72:1212-1216. Accepted for publication 8 February 1982. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1982.. DOI: 10.1094/Phyto-72-1212.

Incidence of pitch canker disease among 550 ramets in 28 clones in a 16-yr-old loblolly pine seed orchard varied from 2% of nine resistant clones to 39% of nine intermediate clones and 92% of 10 susceptible clones in 1976. Some branches died back after inoculations in all months of the year, but more dieback resulted from fall and winter inoculations than from those in spring and summer. Seventy-one percent of the dieback from inoculations happened in May–July regardless of when inoculations were made. Since more dieback developed from inoculations of wounds on susceptible than on resistant or intermediate ramets, resistance does not appear to involve penetration. Spores of Fusarium moniliforme var. subglutinans were present throughout the 1977 growing season on dead branches in the crown, in rainwater falling through infected trees, and in the air; the total indigenous inoculum was sufficient to cause up to 52% of wounded pine seedlings to die back. Nevertheless, symptoms of pitch canker from 1977 natural infections were extremely rare in 1978. In spite of the high incidence of pitch canker in the orchard in spring 1976, cone and seed production was more than twice as large in 1976 as in the preceding 3 yr. Cones initiated in 1975 and 1976 during the pitch canker epidemic matured into record crops in 1976 and 1977. Although resistant ramets produced a plurality of cones most years, intermediate and susceptible ramets also yielded heavy crops in 1976 and 1977.