Alder Tree Diseases

Updated February 21, 2017

If you have an alder tree in the United States, it is one of many that were introduced to North America. The alder trees are native to the North African countries, from Morocco to Tunisia. They can be found growing as far north as Russia and Siberia. Alder trees were introduced to the United States and Canada in the colonial times, and they are now a valued tree species of the new world. Alder trees are regarded as having very little disease and insect problems. However, like many other trees, they are often faced with disease. These are some of the more common alder tree diseases.


Alder trees are from the botanical family, Betulaceae, and their botanical name is Alnus glutinosa. Considered a pioneer species, the alder trees are a birch tree species. They can grow to heights of 20 to 30 meters tall, and they live for about 150 years. New trees can sprout up from the rooting system of a dead tree. This deciduous variety produces rounded leaves that turn reddish or brown in colour, before they fall in late autumn.

Phytophthora alni Infection

Phytophthora alni is a noteworthy alder tree disease that drastically affects the lives of these trees. It is a highly virulent hybrid species. Its exact origins are under investigation, because of its ability to kill entire alder trees.

Didymosphaeria oregonensis Infection

Didymosphaeria oregonensis is a fungus that causes deformation in young alder trees, according to Forestry Development in British Columbia. The fungus was discovered on red alder, Sitka and mountain alder trees. However, as the tree matures and grows a thicker bark, the fungus is rendered ineffective, though traces of the previous damage will remain.

Alder Blight Aphid and Alder Psyllid

Alder blight aphid and alder psyllid cause damage to the alder tree leaves, which--if allowed to affect many of a tree's leaves--will cut off its oxygen and photosynthesis cycles. This will mean that the leaves will not be present to take in the sun's rays for nutrient production, and it will not be able to absorb carbon dioxide from the air, in exchange for its oxygen release. Protecting the alder trees from the alder blight aphid and the alder psyllid will lengthen the life of the tree.

Other Diseases

According to STIHL, alder trees can face several other diseases. Artist's bracket is a tree fungus, and a birch leaf-roller causes the leaves to wilt and roll up. Blushing bracket is another fungus that affects the trees, and chicken of the woods is a yellowish fungus that makes brown rot form on the trees.

Furthermore, other diseases listed by STIHL include powdery mildew, spring hazelcup, willow bracket, tinder bracket, lumpy bracket, and the common sawfly. Detailed information and images of these, and other alder tree diseases are available online at the STIHL website.

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About the Author

Naima Manal's articles on health, diet, nutrition, alternative medicine, education, parenting, crafts, travel, home and garden and home improvement have appeared on various websites. Manal received her Bachelor of Science in biology/pre-medical studies from Molloy College in 1994 and has been a freelance writer, teacher and homeschooling mom since 1993.