Spruce needle rust
Damage, symptoms and biology
The fungus causes rust on the current year's needles and varying degrees of defoliation. The infected needles dry out, turn red, die and drop off. The pathogen over winters on the foliage of a small plant called Labrador tea (Ledum groenlandicum Retzius.). In spring, a first type of spores develops and spreads the disease to other Labrador tea plants. At the start of summer, a second type of spores appears on Labrador tea plants and they infect the needles of spruce. Tiny red dots appear on the infected needles, and a third type of spores develops on these spots. Around the middle of the summer, white pustules containing mature spores ranging from orange to yellow in colour become visible; these spores end up infecting some new Labrador tea plants.
To reduce the risk of disease, spruce trees should not be planted in areas with large numbers of Labrador tea plants, such as in very wet or swampy zones.
Canadian Forest Service Publications
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