Diseases in Trees: Soil-borne Fungal Infections

Do you have a tree that’s in a state of catastrophic decline? Is the foliage pale, dying back in large sections, or even throughout the whole tree? More likely than not, the cause of a widespread dieback can be found in the soil — via chemicals, construction damage, poor water or nutrient conditions, or bacterial or fungal infections. Today we will spotlight two of the most common fungal infections that we encounter in the field: Verticillium wilt and Armillaria root rot.

Verticillium attacks a wide variety of trees and other plants; it is frequently found in maple, box elder, ailanthus, redbud, ash, fruit trees, as well as a number of shrubs and garden vegetables. Honeylocust, birch, and sycamore, sweetgum, and oak are among a few trees with a high resistance to the disease. The fungus typically enters the tree through natural abrasions in the roots, then makes its way to the tree’s xylem tissue — the vascular structure that carries nutrients and water upward. Verticillium causes yellowing and shriveling of the foliage along the pathway of infection, and you can readily identify the fungus by looking inside the cuts when you clip or trim your plants. If you see blackened bands or splotches in the wood, that’s a clear sign of Vertciillium.

The fungus can grow quite vigorously, but can be somewhat controlled by heavy watering — Verticillium does not thrive well in low-oxygen conditions, so it is possible to “drown” the fungus in the soil. (Be sure not to over-water your trees so much that the roots drown as well!) When clipping infected branches from a tree or shrub, be sure to sterilize your trimming tools in between cuts so that you do not transfer the fungus into healthy vascular tissue. If the tree is beyond repair and needs to be removed, be sure not to plant a new tree in the same infected soil. Planting grass for a year or two will help to kill off any remaining soil-borne fungal beds.

Armillaria is famous for being the largest living organism on earth, due to its ability to clone itself over vast tracts of territory. Found worldwide, this fungus also enters the tree through soil contact and dissolves the cell walls of infected plants, leaving bleached-looking wood and causing yellowed foliage and extensive dieback. In the advanced stages of infection mushrooms can be seen growing from the roots or trunk, and sloughing bark may reveal a layer of white fungus underneath. Disastrous as it sounds, Armillaria tends to attack trees that have already been stressed by other factors, and keeping healthy growing conditions can do a lot to stem the spread of infection.

One rather fascinating thing about Armillaria is that exposed, heavily infected wood can actually glow in the dark! The musghroms can glow as well, casting a beautiful greenish or bluish bioluminescence. So if you’ve ever wandered through an enchanted-looking forest or seen one in a movie, chances are what you’re seeing is a widespread, deadly fungal infection. Ah, the dichotomy of nature!

Our experts have decades of experience working with diseased or dying trees, or giving healthy trees the touch-up they need to become outstanding specimens. As always, contact our ISA Certified Arborists for all your tree care needs!

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