Pine Needle Rusts
Pine needle rusts

Click for larger image White pustules of a pine needle rust on mugo pine (Pinus mugo). A. Kunca, National Forest Centre-Slovakia, Bugwood.org

Pine needle rusts are caused by over 20 species of Coleosporium the most common being C. asterum. It results in browning needles and the loss of lower branches. It is rare in the St. Louis area but may affect Austrian, jack, red, Scots, mugo, and ponderosa pines.

Symptoms and Diagnosis

The first sign of the disease is small yellow spots on the needles in fall and throughout the winter. In spring the spots develop spore-producing structures and the needles brown and die resulting in needle drop and the loss of lower limbs. Young pines are most affected.

Life Cycle

Pine needle rust requires an alternate host to complete its life cycle. Goldenrod and asters are most common. Infection on pine needles begins in late summer or early fall when spores released from the fungus growing on goldenrod or asters infects the needles causing small yellow spots. The fungus grows inside the needle where it overwinters. The following spring the fungus resumes growth and the yellow spots develop into white swelling, which grow well above the needle surface. At this time the disease may be confused with pine needle scale. The spore-producing structures split open and release orange colored spores, which then infect goldenrod and asters nearby. The fungus continues to produce spores that re-infect the alternate host until late in the season when spores that infect pine needles are formed, thus completing the rust’s life cycle. The life cycle is completed in one year.

Integrated Pest Management Strategies

1. Live with the disease. Pine needle rusts do very little damage to mature established trees. Young trees or trees grown in a nursery may require more aggressive action.

2. Remove the alternate host. Pine needle rust needs both pine needles and an alternate host of goldenrod or asters to complete its life cycle. Removing these alternate hosts near pines that suffer from the rust disease can break the cycle.

3. Plant resistant species. Replace susceptible pines with Colorado or Norway spruce. White pine is resistant but is not an ideal choice for the St. Louis area.

Organic Strategies

All of the recommended IPM strategies are strictly organic approaches.

More images:

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Brown rust pustules (Cladosporium asterum) on the underside of goldenrod leaves (Solidago speciosa); alternate hose is pine (Pinus)
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Brown rust pustules (Cladosporium asterum) on the underside of goldenrod leaves (Solidago speciosa); alternate hose is pine (Pinus)
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Pustules (aecia) of rust on Scots pine needles (Pinus sylvestris) releasing spores. P.Kapitola, State Phytosanitary Admin, Bugwood.org
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Fruiting bodies of a pine needle rust on red pine needles (Pinus resinosa). USFS-North Central Research Station Archive, USFS, Bugwood.org
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Pine needle rust on mugo pine (Pinus mugo). A. Kunca, National Forest Centre-Slovakia, Bugwood.org
 
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