Effect of Stem Rust Fungi on 45-yr-old Jack Pine. D. W. French, Professor and Department Head, University of Minnesota, St. Paul 55108. Dale L. K. Smeltzer, Research Assistant, and N. A. Anderson, Professor, Department of Plant Pathology, University of Minnesota, St. Paul 55108. Plant Dis. 67:26-28. Accepted for publication 7 May 1982. Copyright 1983 American Phytopathological Society. DOI: 10.1094/PD-67-26.

A plantation of jack pine (Pinus banksiana) surveyed for stem rust infections in 1958 when 25 yr old had 34% of the trees with sweetfern rust (Cronartium comptoniae) infections on the main stem. In 1978 this stand was sampled again, and 49% of the trees had sweetfern rust cankers on the main stem. A significant number of sweetfern rust cankers were not visible until 1978. Cross sections through a sample of these "latent" cankers indicated that the infections had been present since the trees were very young. Diameter of infected trees at 1.4 m was reduced with increased stem circumference affected by the sweetfern rust. Trees with pine-oak rust (C. quercuum) infections had slightly higher mortality and slightly smaller diameters than rustfree trees. The incidence of decay was low in 25 sampled trees.