Yellow is not one of my favorite colors. As a gardener, I should love it – after all, it is the color of the sun. However, on the dark side of gardening, it signifies trouble when a beloved plant is turning shades of yellow and struggling to survive. It is often difficult to course correct this issue once it starts and it now can go one of two ways. The plant lives on with a little or perhaps no course correcting, or it dies regardless of our best efforts.
I was at this crossroads recently with the spruce trees in my wood lot. The needles on the ends of the branches were turning yellow, with the bottom branches most severely affected. I agonized over what it could be and what to do about it. I concluded that these were spruce needle rust symptoms. What is spruce needle rust, you ask? Well, let’s read on to learn more and discover how to treat spruce needle rust.
So, how do you go about identifying spruce needle rust? Forgive the visual, but from a distance, a tree afflicted with spruce needle rust reminds me of a person with frosted hair tips. This image of Guy Fieri from Food Network pops in my head or even Mark McGrath when Sugar Ray was in its heyday in the 90’s. But you probably need more descriptive spruce needle rust symptoms than that in order to make a positive identification.
What is spruce needle rust? There are two fungi responsible for spruce needle rust: Chrysomyxa weirii and Chrysomyxa ledicola. While both of these fungi foster spruce needle rust symptoms in trees, they do so in slightly different ways. Most spruce species are susceptible to the disease but it is most prominent in white, black and blue spruce.
Chrysomyxa weirii: The spruce needle rust caused by this fungus is also known as Weir’s Cushion. The rust caused by Chrysomyxa weirii is referred to as “autoecious.” What this means is that the life cycle of the needle rust is completed without an additional host. So, it starts with spruce and ends with spruce, there is no intermediary host.
One-year-old needles display pale yellow spots or bands in late winter or early spring, which intensify in color and later develop waxy looking yellow-orange blisters swelling with rust-colored spores. These blisters eventually rupture and release the spores, which infect the newly emerging growth, which, in turn, will exhibit spruce needle rust symptoms the following year. The one-year-old diseased needles will drop from the tree prematurely shortly after releasing the spores.
Chrysomyxa ledicola/Chrysomyxa ledi: The spruce needle rust wrought by these fungi is “heteroecious” in nature. This means that its life cycle is dependent on more than one host. You may wonder why you are being schooled on the life cycle of a fungi. The answer is: It’s very important for effective disease management.
The alternate hosts for the rust produced by Chrysomyxa ledicola are Labrador tea (Ledum groenlandicum) and leatherleaf (Chamaedaphne calyculata). The fungus overwinters on Labrador tea and leatherleaf and spores are produced and released from these alternate hosts in early summer. The spores travel by wind and come in contact with spruce trees, infecting the current year’s needles.
In July and August, the current year needles turn yellow and develop whitish waxy blisters filled with yellow-orange spores. The spores released from these pustules travel by wind and rain to, you guessed it, the alternate hosts, where the spores germinate and infect the evergreen leaves they overwinter on. The diseased spruce tree needles drop from the tree in late summer or fall.
How to treat spruce needle rust is probably first and foremost on your mind if you’ve ever been confronted with it. Even though spruce needle rust is caused by fungi, a fungicide treatment is not recommended for spruce needle rust control. Why? Because once the tree displays symptoms, it’s already too late.
The needles are already infected and can’t be cured. If you’re thinking about annual fungicide sprays in order to be pro-active against spruce needle rust, I would advise against that as well because spruce needle rust infections are hard to predict and don’t happen every year. It may linger for a year or two but is not known to excessively overstay its welcome.
Spruce needle rust also does not kill trees; the damage is primarily cosmetic. It also does not prevent the formation of healthy buds on the ends of branches nor the production of new needles the next year. If you identify your rust as being caused by Chrysomyxa ledicola, you could remove any Labrador tea and leatherleaf plants (the alternate hosts) that are found within 1,000 feet (304 m.) of your spruce trees in order to stem the spread.
Rhizosphaeria symptoms on blue spruce
Reader question: I planted several Colorado spruce and Norway spruce a few years ago. While the trees seem to be doing fine and are covered in new growth right now, two of the Norway spruce have bare spots where the branches lost their needles. What’s happening?
Roots and Shoots: While spruces are pretty hardy trees there are a few things that can cause problems. Diagnosing the issue will take a little more observation and information.
Spruce does best with full sun, acidic soil and adequate water. They’re adapted to colder climates like ours, and in hot, dry conditions, spruce will suffer. Both of your varieties, Colorado and Norway, are susceptible to drought and even mature trees will need watering, just an inch per week, when there isn’t sufficient rainfall.
Healthy needles on a Norway spruce.
If any of these needs aren’t met, the tree might still grow, but it will be weakened and more susceptible to pests and disease. Mistakes made when planting can also affect it. Planting it too deeply or shallowly, burying it in more than 2 to 3 inches of mulch or mulching up to the trunk will prevent the tree from thriving and these mistakes are hard to correct later.
First, try to rule out any issues caused by not meeting these conditions for optimal health. A soil test will determine the quality of nutrients the tree is getting and observation will tell you a lot about everything else.
Pest damage could be detected by checking for the signs of the spider mite, a common spruce invader. Evidence of spider mites could be as obvious as a white web with eggs on a branch or more subtly as discolored needles if the mites have been feeding on it. They’ll go dormant in hot weather, though. The best time to find them is in cooler weather. If you find that the mites are widespread throughout the tree, it might need a pesticide and calling an arborist for assistance will get the best results.
There are several possibilities for damage caused by funguses and pathogens. The range of diseases that infect spruce surprised me. The Illinois Cooperative Extension office has a helpful online resource that identifies the most common. The possibilities that could cause damage like what you’ve described include root rot and spruce needle rust.
Root rot symptoms could be exhibited through dead branches, brown needles and make it look like it’s dying. Although you described your tree as having a lot of new growth, the damage could be in an early stage.
Spruce needle rust has been found throughout our area since the 1990s and infects many trees. It doesn’t usually kill them, but makes them look bad by causing the kind of bare spots that you describe and it gets worse over time. A close look at the needles will help identify it.
A bare spot on a Norway spruce could be caused by site conditions, pests or a fungus.
The needles will have yellow bands in spring and then show broken pustules. That’s the sign that the fungus is releasing more spores to infect the tree. The issue usually develops lower on the tree, too, so it could explain bare spots on lower branches. It will eventually work its way up the tree. You can find images of infected needles online to help identify it.
Pruning infected areas of the tree early on may help contain it. A fungicide can be applied by an arborist if the problem needs more attention. In either case, if the tree is valuable to your landscape, and most are, contacting a professional for help is always a good choice. An arborist is one possibility and the Putnam County Cooperative Extension Office offers diagnostic services, too, that are either free or low cost and they can also help you figure out a plan to save the tree. (More about rust here.)
As our climate warms and we’re faced with summer droughts and heat waves more frequently, doing everything we can to help preserve these native trees is worth the effort. Our forests are struggling with climate change, new pests and pathogens and challenges from invasive plants. Closely observing changes in our landscape can catch the kinds of problems you’re noticing quickly before it becomes too advanced.
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