Pine needle rust
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)|
Host plants in Pinaceae
P. Kapitola, Bugwood.org
Spore producing structures sticking out on needles infected with pine needle rust.
- Yellow to orange spots or bands appear on green needles in spring. Needles turn partly or completely yellow.
- Late spring to early summer, tiny raised white tubes form on needles breaking open to release powdery, orange spores.
- Infected needles may remain attached for several years.
- Severe infection causes needles to die, turn brown and fall off.
- Lower branches of young trees are most severely affected.
Host plants in Asteraceae
- Infected leaves develop yellow leaf spots on the upper leaf surface and raised orange spore-filled pustules on the lower leaf surface.
- Powdery yellow-orange spores are produced on the lower leaf surface all summer long.
- Dark brown spores appear within leaf spots on the lower leaf surface in late summer and fall.
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.
- Pine needle rust is a minor stress on the tree and no management is required.
- Increase the vigor of infected trees by watering during dry conditions and mulching to conserve water.
- Removal of alternative hosts such as wild or cultivated species of aster (Aster), goldenrod (Solidago), and several other members of the daisy or aster family (Asteraceae) from the immediate area of the trees will reduce infections of pines (Table 1).
- In areas with large numbers of wild asters, plant conifers resistant to needle rusts like spruce, white pine or balsam fir.