Watch Out for These 5 Evergreen Tree Diseases

When you take the time and effort to plant trees in your yard to improve your landscaping, you want to make sure that things stay looking beautiful. That means tasks like watering, pruning, and fertilizing, but are you also watching them for problems? You don’t want to put all that work into your trees only to see them suffer from a disease and need to be removed. Part of caring for your trees is looking for signs of fungus or infestations.

Like deciduous trees, evergreen trees are also prone to such diseases. Don’t panic if you do discover a problem, though. Identifying the disease in its early stages and taking timely action can make all the difference and help you save your favorite evergreen.

Here’s a list of five evergreen tree diseases that are very common:

1. Cytospora Canker of Spruce

This is a fungal disease that is extremely common in Norway spruce and Colorado blue spruce. Occasionally, it also attacks Douglas fir, hemlocks, larches, and balsam fir.

One of the telltale signs of the disease is dying lower branches and needle browning. As the disease makes its way through the tree, the higher branches also start showing signs of damage. Cankers are also noticeable at the base of the branches, near the trunk of the tree. In Norway spruce trees, cankers may also develop right on the trunk of the tree, resulting in girdling and eventual the death of the tree.

The fungal spores are easily disseminated through wind-driven rain, splashing water, and pruning with shears that have touched the spores. They can also be transported by insects and birds. If there are any open wounds on the body of the tree, it’s easy for the spores to become established and make their way into the tree. Trees with weakened roots and low vigor are more prone to getting the disease.

Remedies for disease management include scheduling regular pruning by professionals, controlling insects and mites, fertilizing as recommended, watering the soil thoroughly, and vertically mulching to relieve soil compaction.

2. White Pine Weevil

This is one of the most destructive insect pests in North America. Neither the Colorado blue spruce, Norway spruce, Serbian spruce, nor Douglas fir is safe from the wrath of this pest.

The insect larvae can chew the stem entirely and leave it hollow. You may notice the tree wilting, drooping, and ultimately dying. It’s also possible that a side branch could become bent and start growing upward while serving as the main site for the pest. You may also notice glistening resin droplets from the tree due to the punctures made by adults during the egg-laying stage.

Several years after an attack by this pest, a few lateral branches may start growing from unexpected sites, resulting in a permanently forked tree.

The best way to manage this disease is by pruning and burning the infected branches as soon as you notice them. Ideally, all shoots but one live lateral one should be pruned to promote single-stem dominance. Another option is to apply insecticide when the first droplets of resin are detected. However, bear in mind that insecticides are highly poisonous and should only be applied under professional supervision.

3. Cedar Rust Disease

Cedar rust disease cankers on evergreen tree.Evergreen trees are very prone to rust diseases. The first symptoms of this fungal disease are the powdery orange or red spores on the leaves or needles. Even though the spores are initially underneath the leaves, they slowly move to the upper side as the disease progresses. You may also notice the leaves wilting and falling off.

Certain types of rust fungus can also result in the evergreen trees developing cankers or witch’s brooms. The best to tackle the disease is by scheduling pruning to get rid of the infected needles, leaves, or branches. Make sure to get rid of any debris around the base of the evergreen and dispose of it safely. Lastly, keep in mind to water the tree below the branches and never directly wet the leaves, as this can create the perfect ecosystem for the fungi to breed further.

4. Bagworms

While it is extremely difficult to notice bagworms, it’s hard to miss the homes they make in your trees using their silk. The diaphanous cocoon-looking bag can be filled with over 1,000 eggs at any given time. Out of all species of trees, evergreens such as juniper, arborvitae, cedar, and spruce carry a higher risk of getting attacked by these worms.

The worms usually eat up the buds and foliage, resulting in the branch tips becoming brown and then dying. But if the disease remains unchecked and the worms end up eating 80 percent of the tree, your entire tree might die. Moreover, the “bags” wrapped around the twigs to build their home can also kill the tree in just a few years.

It sounds gross, but the easiest remedy for the disease is cutting off the silken bags by hand and destroying them. You’ll also need to ensure that you are getting rid of all the silk that can otherwise strangle the twig. Apart from that, calling a certified arborist to apply a special treatment to the entire tree is an option. Ideally, the treatment should be applied during the early days of summer or late spring to target all the active larvae.

5. Rhizosphaera Needle Cast

The final disease to make our list is Rhizosphaera needle cast. This disease is especially challenging to spot. It takes close to five months for visible signs to appear. The Colorado blue spruce is particularly at risk of being infected with a needle cast disease.

Rhizosphaera needle cast first infects needles on the lower branches and then gradually moves upward. The stomata of the infected needles can also end up with tiny fruiting bodies of the Rhizosphaera fungus. During monsoon, the fruiting bodies release the spores later deposited on new needles, and the infection starts spreading through a new cycle.

If you are planting blue spruce, make sure to thoroughly inspect the foliage for fruiting bodies of Rhizosphaera protruding through needle stomata. Refrain from planting the tree even if you notice a single fruiting body. Arborists also recommend vertical mulching to improve the aeration and water penetration, both of which play a crucial role in reducing the severity of the disease. Finally, make sure not to shear the trees when the foliage is wet, as that may result in spreading the disease.

This list may sound scary, but with the guidance and advice from trained arborists, it’s possible to avoid the infestation or evergreen tree diseases entirely. Contact Mr. Tree right away to find out how we can help you.


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