Abstract
The progression of pitch canker disease, caused by Fusarium circinatum, was followed over 4 yr (1992–1996) in urban stands of Monterey pine, Pinus radiata, with initially zero, light, moderate, and severe disease intensity. The disease progressed from a few to many branch tip symptoms, followed by the appearance of cankers on the main stem. Symptomatic branch tips at the start of the study were predictive of tree mortality or removal after 4 yr. Trees with canopy dieback and stem cankers were often attacked by the red turpentine beetle, Dendroctonus valens. Among initially disease-free trees, disease progression and final severity were greater in plots with initially severe and moderate disease intensity. Apparent infection rates did not differ between plots with different initial disease intensities. Over the 4 yr of the study, 2% of trees in the five plots with most severe disease never exhibited disease symptoms and thus may be resistant to pitch canker. In addition, 7% of symptomatic trees in these plots never had more than two symptomatic branch tips, which may reflect a moderate level of resistance. FOR. SCI. 48(4):694–700.