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Symptoms and Causes of Evergreen Tree Diseases

December 08, 2023

Evergreen trees are at the forefront of this holiday season, and we do get a lot of questions about browning in conifers at this time of the year, especially pines, cypresses, junipers, and cedars. Most of the time, this is caused by seasonal needle drop, which is not damaging at all, but can be alarming. If you have concerns about the late-season condition of your evergreens, give us a call! Regularly inspecting the tree for any signs of discoloration, wilting, or unusual growth patterns can help you detect problems early. , Below we explore the symptoms and causes of 4 evergreen tree diseases.

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Rhizosphaera Needle Cast

Evergreen trees are susceptible to a fungal disease called Rhizosphaera Needle Cast. This disease can cause coniferous trees to lose their needles prematurely, turning them brown before they fall off. If left untreated, the symptoms can worsen, leading to severe defoliation and even tree death.

Symptoms of Rhizosphaera Needle Cast

  • Discoloration: Infected needles may turn yellow or brown, starting from the lower branches and gradually moving up the tree.
  • Tri-colored girdled needles: Needles may have green, brown, and yellow sections, with the brown area strangling the needle.
  • Pycnidia: Tiny black fruiting structures that reproduce spores.
  • Thinning foliage: The tree starts to lose needles, leading to a visually sparse appearance. In severe cases, branch dieback can occur, where entire branches wither and die.

Causes of Rhizosphaera Needle Cast

Rhizosphaera Needle Cast is caused by the Rhizosphaera fungus and can spread rapidly if left untreated. The fungus spreads through the release of spores from fruiting bodies. These spores can be transferred to other trees and plants, leading to further infection. To prevent the spread of Rhizosphaera Needle Cast, thorough inspection of foliage and careful removal of infected branches is required.

Cypress tree with discoloration - evergreen tree diseases - Burkholder PHC
Norway spruce with cytosphora canker - Burkholder PHC

Cytospora Canker

Cytospora canker is a highly destructive fungal disease that affects evergreen trees and is known to infect weakened trees. The fungus enters the tree through wounds, causing the bark to crack and ooze a resin-like substance. The infection can spread rapidly, causing the branches to die off and eventually killing the entire tree if left untreated.

Symptoms of Cytospora Canker

  • Lower branch dieback: Infected trees often exhibit a gradual decline in the health and vitality of their lower branches. These branches may show signs of wilting, turn brown or gray, and eventually die.
  • Poor growth: Trees affected by Cytospora Canker may appear stunted or have reduced vigor compared to healthy trees. The result is thin, sparse foliage and a general lack of vitality.
  • Needle discoloration: Faded or brown needles are common signs of this fungal disease. The needles may lose their vibrant green color and become discolored or brown. This symptom is often more noticeable in older needles than new growth.
  • Resin: Sticky, amber-colored resin may appear to ooze from cankers or cracks in the branches, serving as a defense mechanism for the tree.

Causes of Cytospora Canker

Cytospora Canker is caused by the fungus Leucostoma kunzei. This fungal infection primarily targets spruce trees. The fungus can spread through different means, such as rain, wind, and insects. When

raindrops hit an infected tree, the fungal spores can be carried by the raindrops to nearby healthy trees, which can cause the disease to spread. Additionally, wind can transport these spores over long distances, affecting a much larger population of spruce trees. Furthermore, insects, including beetles, can carry the spores on their bodies.

Mature spruce trees are prone to contracting Cytospora Canker disease, especially when stressed due to drought or poor care. When a tree lacks sufficient water or proper tree care, that tree becomes more vulnerable to fungal infection. The fungus exploits the tree’s weakened state, resulting in development of Cytospora Cankers.

Cedar Rust Disease

    Cedar Rust Disease is an evergreen tree disease and fungal infection that affects various plants, including cedar trees, junipers, and apple trees.

    Symptoms of Cedar Rust Disease

    • Spores: Powdery red or orange spores on the leaves give the infected tree a distinct “rusty” appearance. The spores may appear as small, raised bumps on the leaf surface, often forming in circular patterns.
    • Wilting: Infected leaves may turn yellow or brown and become dry and lifeless before dropping from the tree, which can lead to a noticeable thinning of foliage.
    • Cankers/Witch’s Brooms: Cankers are sunken or swollen areas on the bark, often accompanied by cracked or discolored wood. “Witch’s brooms” are dense clusters of twigs and branches that form in abnormal shapes resembling a broom.

    Causes of Cedar Rust Disease

      Cedar rust disease is caused by a rust fungus that thrives in humid and rainy climates. The disease mainly affects evergreen trees and spreads due to environmental factors such as leaf moisture. The moisture provides the ideal environment for the rust fungus to grow and spread.

      Fungi belonging to the Gymnosporangium family play a crucial role in developing and transmitting cedar rust disease. The fungus generates spores that can travel long distances through the air, are carried by wind currents, and can easily infect nearby evergreen trees. After landing on susceptible trees, spores penetrate leaves and form orange or rust-colored lesions as visible indicators of infection.

      Diplodia Blight

      Diplodia Blight is a common fungal disease that affects various types of trees, including pines, spruces, and firs. Caused by the fungus Diplodia pinea, this blight can devastate these trees’ overall health and appearance.

      Symptoms of Diplodia Blight

      • Stunted needles: Infected trees often exhibit wilted and discolored foliage, which can be easily noticeable. Young needles may turn a tan color but remain attached to the tree.
      • Pycnidia: Small, black fruiting structures often found on infected needles, stems, or branches are responsible for spreading the disease by releasing spores.
      • Infected branches: Widespread infection can lead to significant tree decline if not treated promptly.
      • Cankers: Resinous cankers may form on the tree, creating recessed areas that exude resin. These cankers are visible evidence of the disease’s progression and can cause further damage to the affected tree.

      Causes of Diplodia Blight

      As noted above, Diplodia Blight is a fungal disease caused by Diplodia pinea, an opportunistic pathogen. This pathogen can infect trees through various means and cause significant damage if not appropriately managed. Species such as pines, spruces, and Douglas firs are highly susceptible to this disease, providing an ideal environment for the fungus to establish and spread rapidly.

      Environmental conditions are a crucial factor in the rise of infection rates. Diplodia Blight thrives in warm and humid climates, especially during extended periods of rainfall. Moisture accumulating on tree bark creates an ideal environment for the fungus to grow and invade the tissues, ultimately resulting in an infection.

      Additionally, wounds or injuries to tree branches and trunks serve as entry points for Diplodia pinea. Mechanical damage caused by improper pruning or accidental injuries can allow the fungal pathogen to invade the tree’s defenses and initiate infection.

      Diplodia Blight is more likely to occur in already stressed or weakened trees. Other factors, such as drought, nutrient deficiencies, or insect damage, can make the trees more susceptible to this fungal disease. When the tree’s ability to resist the pathogen is compromised, the likelihood of infection increases.

      Call Burkholder PHC to Protect Your Evergreen Trees

      Are your evergreen trees looking less than healthy? Burkholder PHC is here to help. Our team of certified arborists and plant specialists is well-versed in identifying and treating evergreen tree diseases, staying up-to-date with the latest research, and utilizing the most effective treatment methods. Get a free tree care consultation from Burkholder PHC today.