By: Danny Bagwell, Pioneer Vegetation Manager
As vegetation manager, I receive calls from members for a variety of reasons throughout the year, but this year I’ve received more calls than normal about evergreens in members’ yards losing their green color. You may have noticed that your evergreens don’t look as healthy as they once did. Pine needles are turning brown, and spruce trees are becoming sparse instead of full and lush. Many of these trees that have been in yards for over 30 years are suddenly in a condition that means they’ll likely need to be removed (at the homeowners’ expense). What’s worse is that it’s usually not one, but many trees — along a property line for example.
Why is this happening? Well, there’s not one specific reason, but rather several that could be occurring. Most types of trees have some susceptibility to conditions or ailments. Vulnerability issues are usually caused by common stresses such as drought, native pests, and defects. These issues usually don’t kill the tree but can cause damage.
Some more recently occurring issues are related to fungal diseases, including:
Rhizosphaera needle cast Rhizosphaera needle cast can be found in spruce trees and causes premature death and casting of needles. The Rhizosphaera kalkhoffii fungus can survive on living and recently killed needles throughout the winter, and then from spring to early fall, fungal spores spread to new needles or neighboring trees. Damage and symptoms typically begin on the lower branches and move up the tree. Trees can be protected from Rhizosphaera needle cast with properly timed fungicide applications. Unfortunately, there’s no method that will remove Rhizosphaera from spruce trees.
Diplodia tip blight Then there’s Diplodia tip blight in Scots and Austrian pines. The Diplodia fungus commonly attacks mature trees that have been under stress from drought, root restriction, or other planting site problems. This disease is characterized by the blight, or dieback of the tips of branches that can usually be seen from a distance. Repeated infections over several years can cause the tree to look brown, branches to die, and the tree to become deformed. If trees with Diplodia tip blight are left untreated, they can eventually die.
Dithistroma needle blight And finally, Dithistroma needle blight in pines causes blight — reddish-brown spots can be found scattered on green needles, eventually causing a brown band to form and then the entire needle to turn completely brown and fall off. This usually begins on the needles closest to the trunk and spreads outward to the ends of the branches. Signs of this disease typically begin between late summer and fall. However, if the disease is recurring, brown spots and dead needles may appear anytime during the year.
Fungal diseases are accelerated during wet springs when fungal spores affect the needles, followed by an early, hot summer like we’ve seen the past two years. Some diseases are manageable through changing seasons, dormancy, tolerances, beneficial bugs, or even treatments.
Fungal diseases may attack needles anytime during the growing season, but spring infection is most common. When trees become infected, they will continue to lose the past years’ needles, which leaves only the current year’s growth. Even if treatment is applied, the branches where the needles have died and fallen off will not generate new needles.
Homeowners often seek methods to “cure” affected trees. Before deciding on a treatment plan, homeowners should first consider a few things. First, what value does the tree provide? Is it a windbreak or a privacy fence that would be difficult to replace? Second, what is the long-term investment necessary to apply fungicides to infected trees? You’ll likely need repeated applications for multiple years to improve the tree’s health and appearance, which can be expensive. In cases where the tree is too disease-ridden for treatment, there is no option but to replace it.
Sometimes there can be a positive takeaway from these diseases. Some trees develop a resistance to a disease because they were able to fight it off. We are seeing trees such as American Elm and chestnut slowly coming back into our landscape, with tolerances to withstand certain issues.
As a rule of thumb, it’s a good idea to have a certified arborist look over your property and check your trees. A certified arborist can spot issues in trees before they become severe and advise treatment options before it’s too late.