Spruce tree needle rust appearing in northern MN
Homeowners in northern Minnesota are noticing their spruce trees turning tan, yellow, orange or sometimes, pink. Most likely these trees are infected with the spruce needle rust fungus, which presents an aesthetic problem but seldom a tree health problem, according to the Minnesota Department of Natural Resources (DNR).
Spruce needle rust infects current-year needles of blue spruce but can also be found on white and black spruce. Infected needles will turn yellow and then shed in the fall. However, healthy buds on the ends of the branches will produce new needles the following year.
“Seeing favorite ornamental trees turn a rusty color and appear to be dying can cause concern, but homeowners shouldn’t rush to cut them down,” said Mike Albers, DNR forest health specialist. “The fungus only infects the current year’s needles, and does not spread from tree to tree.”
In some years, like this one, spruce needle rust is very common; but in most years it is difficult to find because it requires other plants and specific growing conditions to complete its life cycle.
In early summer, the rust fungus produces spores on the leaves of Labrador tea or leather leaf, which grow in peatlands, bogs and swamps.
Winds can blow these spores onto current-year spruce needles. If the weather is wet and cool, needles can become infected. Rust fungus produced by the infected tree can reinfect and overwinter on alternate host plants, but this is generally interrupted by changing weather conditions. A widespread infection one year can be undetectable the next.
Chemical control with a fungicide is usually not helpful and cannot cure the infected needles.
Albers recommends keeping spruce trees healthy during a spruce needle rust outbreak by:
- Watering trees during dry times; avoid using sprinklers because the needles will stay wet and can lead to additional infections.
- Mowing weeds and grass around small trees to keep needles dry and prevent infection.
- Mulching around trees to maintain soil moisture and discourage weed and grass growth. Keep the mulch off the tree’s trunk.
Homeowners and other landowners can find information about tree care and tree diseases on DNR website.