….is muttered so often when evaluating trees that the term can almost be believed. Why do leaves stay on some trees all winter, only to fall in the spring? Why did my tree “suddenly” die after I built a pool and patio around it? Why is the foliage on my coniferous tree changing colour at odd times of the year? The questions are sometimes to complex to answer, or so obvious that it's hard to explain, especially with the changing colour of coniferous foliage. The big 3; insects, disease and the environment, all cause this symptom in one way or another. One of the most consistent answers is to look for though is needle cast. A fungal infection that attacks all popular varieties of Spruce and Pine trees, and several Fir trees also. Norway Spruce have been found to be slightly more resistant to the disease, but unfortunately, still not immune. Fungal infections can be tricky, not to be taken lightly.
What am I supposed to do?
There are several specific needle cast varieties that infect our trees, but they have consistent signs and repercussions. The spores of the fungus are almost microscopic, and should be tested to pinpoint what is actually attacking your tree. The wrong treatment can damage your trees, and magnify the problems. An accurate diagnosis is always step 1.
What's happening to my tree?
If your tree(s) has been diagnosed with a needle cast infection, it’s important you know what it is going to do to it, or them. The disease probably arrived from a neighbouring tree, through the rain and the wind. You won't see your tree become infected, the wind and rain will leave their calling cards though. It is somewhat transportable via insects and other wildlife too, which can give the disease a much longer range.
The 3 faint spots in the yellow patch of this pine needle give a good indication on the subtlety of the emerging problem. This was taken in the autumn of the 1st year of infection. Once infected though, the fungal spores generally become noticeable in their 2nd year. They come to life in the spring, when wet conditions are favourable. Given the prairie climate, every spring is wet and this is why this disease is prominent in Manitoba. If excess moisture lingers and high humidity continues around the foliage, the fungus will only grow and make it harder to deal with. It’s really beneficial for trees to be adequately spaced to allow good airflow and speedier drying in damp environments. Consideration of mature size at planting can be key to prevent unnecessary situations too.
As the infection enters its 2nd year, it still goes virtually undetected until well into the summer. From the spring time, until you see the foliage changing colour, the spores of the fungus are busy growing into, and clogging, the stomata of the needles. The stomata are how the tree exchanges gases with the environment, and unable to breathe the needles begin to die. Depending on the species of tree, the foliage can change colour from yellow, to red, to brown, to purple. The needles in the picture to the right have infected this twig for 2 years. Much more noticeable after some solid incubation time, and more obvious damage to sound the alarm bells.Keep an eye on the colour of the needles throughout the year, early detection is key to successful treatment. Small lesions on the foliage is a good sign there’s something up.
When should I be inspecting my trees?
The banding and discoloured tips on this pine foliage are good signs of a localised needle cast problem. Trying to see spores as tiny as they are can be difficult, made even harder with the fact they don’t have a schedule. Best times to spot them are after a rain fall, during high humidity. It’s these conditions that promote growth. If you have sprinklers splashing your trees everyday, this is not helping and needs to be stopped. As the fungus begins to erupt spores from the needles, any moving water is spreading them; onto new growth, other parts of the tree, and the ground. If you have neighbouring trees that are susceptible, they can be unnecessarily infected too.
Once infected, sanitation is key. Diseased needles will become weakly attached to twigs as the disease advances, or possibly fallen by late summer. Washing your tree toward the end of the growing season, and removing and destroying the needles, is crucial at the beginning of treatment. The pathogen overwinters on the infected needles and getting it our of the vicinity of the tree is helpful. If you have mulch surrounding your tree, which is beneficial for many reasons, removing the top layer and adding some clean material is recommended. It may be a frustrating task, but it’s the little things can make a huge difference. Like a lot of fungal problems, they are tough to control. Diligent management is needed to try and eliminate the spores from the environment, but is achievable with a little commitment and hard work.
Can I just spray my tree?
Chemical control* will not “cure your tree.“ Your diligent efforts to eliminate the fungus from the area, and keeping it clean will. Registered fungicides will give you your best chance of keeping it down while you get to work on your tree. They need to be applied early spring, and ideally 2 or 3 more times through the year, but other factors can reduce the need for excessive applications of pesticides. The weather will determine how often you should spray for best management of the pathogen. If your tree is not treated properly, the disease will spread, slowly killing branches and diminishing aesthetic value in older trees. The tree here has never been dealt with, and the lower branches have been defoliated, and lost much of its charm. Younger trees, especially saplings, can be heavily defoliated and die if repeat infections occur.
As with any tree in the urban environment, regular watering and root zone attention are essential to the trees long term development and survival. Backyards and sidewalks are not natural for a tree, and will leave them exposed to all sorts of problems as they grow older, it’s up to us as tree owners to keep them healthy for themselves, the community and for our planet. This scots pine below is well maintained and lived into old age, with a little love and dedication there's nothing stopping us from all having trees this healthy and beautiful lining our streets and parks.
*With any chemical use, please ensure it is registered for use in your local area. Always follow the labels accurately, or consult licensed applicators if your trees are too large for you to apply effectively. Applying incorrect products, or in an unsafe manner, can lead to dire consequences ranging from water pollution to wildlife death.