Scout trees now for spruce needle rust

Spruce needle rust can cause spruce trees to lose 25 to 75 percent of their new needles. Know how to reduce the impact of spruce needle rust to your Christmas tree fields and landscape.

Rust fungi represent some of the most advanced fungal species known. Because rusts are complex diseases, they can be described in many different ways. You can categorize them by their life cycles, spore colors, primary or alternate hosts, or the types of symptoms they cause. Using both symptoms and the conifer host is probably your best bet in identifying the rust diseases of Christmas trees.

Basically, there are two types of rusts on Michigan Christmas trees: those that cause diseases of stems and twigs and those that cause diseases of needles. An example of needle rust that is beginning to show up on spruce trees in Christmas tree fields and landscapes in the Cadillac, Mich. area is spruce needle rust. Scouting trees now, you will find needles that have yellow bands with small, yellow-orange pustules.

Spruce needle rust
Discolored needles and foliage from spruce needle rust.

Spruce needle rust overwinters on Labrador tea and leather leaf, and spores from these alternate hosts have moved to the spruce trees via wind and rain events and are now infecting spruce trees. In July and August, yellow, current-year needles with whitish blisters filled with yellow spores will appear on Colorado blue, black and white spruce. Shedding of infected needles will follow these infection episodes. The alternate hosts, Labrador tea and leather leaf, are members of the Heath family and are found in bogs and damp thickets.

White to orange blisters
White to orange blisters on current-year needles.

Care should be taken to plant spruce away from wetlands, especially the rust-susceptible Colorado blue, black and white spruce. Norway spruce is more resistant. The only control options are to scout for alternate hosts, rogue infected branches and trees, and plant resistant stock. Following these activities can reduce the impact of many of these rust diseases.

Tree with spruce needle rust
Tree with orange hue from spruce needle rust.

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