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Extension > Garden > Yard and Garden > Pine needle rust

Pine needle rust

Rebecca Koetter and Michelle Grabowski

Importance

Pine needle rust is a disease that discolors needles, slows tree growth and may disfigure needles on young pines with 2 or 3 needles per bundle (Table 1). Management is rarely required because needle rust does very little overall harm to well-established trees.

Pathogen and susceptible plants

Pine needle rust is a native fungal disease caused by Coleosporium asterum. Like many rust fungi, C. asterum needs two different host plants to complete its life cycle; one plant from the Pinaceae family and the other from the Asteraceae family.

Table 1: Plants infected by Pine Needle Rust in Minnesota

Host Plants in Pinaceae Host Plants in Asteraceae
Most commonly affected: Most commonly affected:
Austrian (Pinus nigra) Aster (Aster)
Jack pine (P. bankisana) Goldenrod (Solidago)
Red pine (P. resinosa) Occasionally affected:
Ponderosa pine (P. ponderosa) Daisy fleabane (Erigeron)
Mugo pine (P. mugo) Gumweed (Grindelia)
Scots pine (P. sylvestris) Goldenaster (Heterotheca)

Identification

Host plants in Pinaceae

P. Kapitola, Bugwood.org

Spore producing structures sticking out on needles infected with pine needle rust.

Host plants in Asteraceae

Biology

M. Grabowski, UMN Extension

Pine needle rust fungus on golden rod.

The needle rust fungus creates multiple unique types of spores that all play a different role in this complex life cycle and allow it to move between pine trees and plants in the aster family. All of the different spore types of the needle rust fungus need moisture on leaves and needles to start a new infection.

The needle rust fungus survives winter within living plant tissue including infected pine needles and infected leaves at the crown of plants in the aster family. Yellow to orange spore producing structures appear as spots or bands on infected pine needles in early spring. By early summer, these give rise to white tube-like spore producing structures which split open, releasing powdery orange spores. The spores produced on pine needles cannot re-infect other pine needles but rather are carried by wind to infect the leaves of a susceptible member of the aster family.

Infected leaves of plants in the aster family produce powdery yellow-orange spores on the lower leaf surface all summer long. These spores can only re-infect another member of the aster family and cannot infect pine needles. In fall, however, a different dark brown spore type is formed on the aster that are carried by wind to infect nearby pine needles.

Management


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