Cause Three rust fungi have been reported: Coleosporium asterum on lodgepole (alternate hosts such as aster and goldenrod) from Washington; C. pacificum (alternate host, tarweed) from Oregon; and C. jonesii (alternate host, Ribes spp.) from Idaho. Generally, basidiospores infect pines in late summer to early fall. Aeciaspores are produced in the spring and infect the alternate host. Urediniospores are produced on the alternate host and may have many cycles during the summer before telia are produced in the fall. Young trees seem to suffer the worst from loss of growth and proximity to alternate hosts, but generally the disease is not a severe problem.
Symptoms Coleosporium asterum-needles may develop reddish-orange dots on yellow spots or bands. A month later, flat-sided, white columns break open at the sides (aecia). Needles may remain on the tree for 1 or 2 years, producing new crops of spores. Young trees may have heavy needle loss on lower branches. Bright orange pustules (uredinia) develop on the aster host. These become reddish brown and crusty (telia). Alternate host may defoliate from severe infections.
C. pacificum-The aecia are very wide and tongue-shaped and may be on all needle surfaces.
Cultural control These rusts generally cause little damage and do not warrant control most of the time.
- Provide good air circulation; do not crowd plants.
- Practice good weed control so lower needles are not kept moist for extended periods of time.
- For high-value trees, remove and destroy fallen needles that collect in branch crotches and on the ground.
Chemical control Protect trees in late summer when telia are seen on alternate hosts.
- Armada 50 WDG at 9 oz/100 gal water. Do not use a silicone-based surfactant. Not for nursery or greenhouse use. Group 3 + 11 fungicide. 12-hr reentry.
- Heritage at 1 to 4 oz/100 gal water plus a non-silicone-based wetter sticker. Registered for conifers including Christmas trees. Group 11 fungicide. 4-hr reentry.
Reference Mihail, J.D., Bruhn, J.N., Meyer, T.R., and Bell, F.W. 2002. Pine needle rust effect on Pinus banskiana in response to interspecific plant competition and telial host density. Canadian Journal of Forest Research 32:1372-1380.