Spruce cone rust (Chrysomyxa pirolata)

(Written by Dr. Herb Cerezke)

Last Review/Updated: January 6, 2003

Spruce cone rust caused by the rust fungus, Chrysomyxa pirolata Wint., periodically damages cones of spruces in localized forest areas and can be a serious problem in spruce seed orchards. Infection in cones seriously reduces seed yield.

Primary Hosts andDistribution

  • White spruce (Picea glauca (Moench) Voss)
  • Engelmann spruce (P. engelmannii Parry)
  • Black spruce (P. mariana (Mill.) B.S.P.)
  • Blue spruce (P. pungens Engelm.) (occassionally)

Spruce cone infections can occur throughout Alberta, but are generally heaviest along the east slopes of the Rocky Mountains. Spruce species are the primary hosts of this fungus but the disease also requires the presence of non-conifer host plants to complete its life cycle.

Disease Cycle

Spruce cone rust infects only the cones of spruces and will not infect the needles. Required alternate host plants for completion of the rust life cycle include wintergreen species such as Pyrola spp. and Moneses spp. Its development is annual and systemic or partially systemic in spruce cones and perennial and systemic in its alternate host plants.

Infection Cycle

In spring and early summer, about the time of cone pollination, basiospores produced on alternate host plant leaves become wind-disseminated and infect young female conelets. Development of pycnia on the conelets follows shortly after, and by mid- to late-summer infected cones turn light brown, dry, and open prematurely releasing masses of yellow-orange powdery spores (aeciospores). All spore types of this rust disease require microscope enlargement to identify.

Aeciospores are wind-disseminated (during July to September) and infect the leaves of alternate host plants in late summer to early fall.

In the following spring, uredinia (with urediniospores) develop on the leaves of alternate host plants and overwinter, producing telia (with teliospores) and basidiospores in the following spring.

Detection and Damage

Look for the following signs and symptoms:

  • Infected wintergreen leaves in mid- to late-summer may be atrophied, chlorotic, and less shiny than uninfected leaves.
  • Diseased cones become evident in mid- to late-summer when they turn light brown, dry, and the scales open prematurely releasing powdery yellow-orange spores (aeciospores).
  • Note orange-colored pustules (uredinia and telia) on the under surface of alternate host plant leaves, indicating presence of the disease.

Up to 50% or more of a cone crop can be infected in localized areas and most of the seeds in infected cones are not viable or show poor germination. Seeds from infected cones generally have reduced weight.

Management

  • Control of spruce cone rust disease is not practical in wild stands of spruce but may be necessary for protection of the seed crop in high value seed orchards.
  • Avoid collecting infected cones in the fall because of their low and poor quality seed yield.
  • Seed orchards established in areas where alternate host plants are abundant are at high risk for infection.
  • Control or reduction of alternate host plants adjacent to seed orchards may reduce cone infection risk.
  • Cone rust infection in seed orchards may be reduced by an appropriately timed fungicidal application.
  • Monitoring certain weather factors such as periods of high humidity and wind conditions can help to predict basidiospore infection of conelets in the spring.