5 Fungal Diseases: April Showers Bring May Tree Diseases

Springtime is the mark of new beginnings and growth; however, not all growth is welcome, especially fungal diseases that may destroy your trees. The cool, moist weather of early spring days, like the weather the Northern VA, DC Metro area has already been experiencing this spring, creates the perfect breeding ground for fungal diseases.

In this article, we discuss the 5 fungal diseases you need to watch out for and begin proactively acting against this April. After all, once the tree fungus starts attacking your trees, there is no going back.


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1. Anthracnose

anthracnose fungal tree leaf disease, curled leaves with brown spots
Curled tree leaves with brown spots, due to anthracnose fungal disease.

Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org

The main culprit behind anthracnose diseases is excess water. Due to the wet and cool humid environment, rainy weather, and tree watering that happens in the spring, trees in the Northern VA, MD, and DC Metro areas become prone to the fungal disease.

If left untreated for years, the trees will become susceptible to secondary invaders, which altogether impacts their long-term health.

Symptoms:

  • Symptoms may disappear during a dry spell, but come back during or after a rainstorm.
  • Younger leaves are likely to appear misshapen (curled, distorted) with brown spots.
  • Mature leaves tend to have dark brown spots on normally shaped leaves, but they may have signs of pest damage.

Targets: Dogwood, Ash, Oak, Sycamore, Birch, Walnut, Tulip, Hickory, and Maple trees

*In the spring, our Certified Arborists see a TON of Dogwood Anthracnose. If you have a dogwood (with the exception of Kousa Dogwoods), your tree should be on a preventative spray treatment this spring*

Learn more about Anthracnose


2. Sooty Mold

sooty mold fungal disease seen on tree leaves: tree pest infestation feeding and black coating
Signs of tree pest feeding and black coating on tree leaves due to sooty mold fungal disease infection.

Daren Mueller, Iowa State University, Bugwood.org

Although not harmful on its own, sooty mold coats tree leaves which indirectly impacts the tree’s health. This coating restricts the tree’s ability to absorb sunlight and interferes with its ability to produce nutrients for itself. Without its needed nutrients, the tree is unlikely to survive.

Additionally, the presence of sooty mold indicates an ongoing problem: an active pest infestation.

Symptoms:

  • Stunted tree growth
  • Early defoliation or leaf drop
  • Tree bugs (lace bugs, scale insects, aphids) sucking up sap from the tree
  • Honeydew residue left behind e

Targets: Rose, Ash, Oak, Elm, Maples, Willow, and Fruit trees

 Learn more about Sooty Mold


3. Powdery Mildew

powdery mildew tree fungal disease on leaf, showing talcum powder-like growth
Fungal disease, powdery mildew, displaying talcum powder-like growth on tree leaf.

Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org

Typically, powdery mildew is carried from one affected plant to a healthy plant through wind.

Similar to sooty mold, powdery mildew coats leaves, which results in the tree not receiving the nutrients it needs to survive. The tree becomes unable to create food for new leaf and growth, which stunts the plant’s growth altogether. Long-term, the tree becomes stressed and will become more susceptible to other diseases or pest infestations.

Symptoms:

  • white to grayish spots or patches on leaves
  • talcum powder-like growth on the upper area of the leaves

Targets: In the VA, DC, and MD areas, the most susceptible are Lilac, Peony, Dogwood, and Crape Myrtle trees.

 Learn more about Powdery Mildew


4. Cercospora Leaf Spot

cercospora leaf spot fungal tree disease brown spots yellow borders
Leaves infected with cercospora leaf spot fungal tree disease; showing round spots with borders.

Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org

The typical wet, warm conditions of spring lead to cercospora leaf spot disease in tree leaves. Symptoms of cercospora leaf spot fungal disease may start as a small spot on the leaf, but as the disease spreads, the spots become more rampant throughout the foliage. As a result, the tree’s leaves stop doing their job and fall off of the tree. Due to the frequent defoliation, the tree’s health will decline.

Symptoms:

  • Round leaf spots, potentially with purple or dark brown borders
  • Tiny black flecks, representing fungal spores, at the center of these leaf spots

Targets: Can affect various species of ornamentals and shade trees, but in our area the most prevalently affected species is white oak trees.

 Learn more about Cercospora Leaf Spot


5. Phytophthora Root Rot

Phytophthora Root Rot tree fungal disease: darkened bark, browning leaves, small leaves, branch dieback
Various phytophthora root rot fungal disease symptoms present on tree leaves.

Daren Mueller, Iowa State University, Bugwood.org

Generally, phytophthora root rot is likely to develop when the soil around the base of the tree remains wet for too long of a time period.

The disease impacts the tree’s root systems, diminishes the tree’s structural integrity, and can lead to additional issues such as property damage and injury. Usually, it won’t immediately lead to tree death, but it will if the tree is left untreated for years.

Symptoms:

  • Darkened bark
  • Suppressed tree growth
  • Yellowing or browning leaves
  • Unusually small leaves
  • Branch dieback
  • Drooping and curling of tree leaves

Targets: Most commonly azalea, rhododendron, dogwood, pieris, yew bushes, deodar cedar, mountain laurel, heather, juniper, Fraser fir, white pine, shortleaf pine, camellia japonica, aucuba.

Learn more about Phytophthora Root Rot


How do you treat fungus on trees?

The best treatment for fungal tree disease is preventative treatment through spray applications. By taking action now, you can save yourself and your trees trouble later.

With that said, if you notice your tree already suffering from a fungal disease, it’s crucial to act on it right now, to make sure the fungal tree disease doesn’t return next year. With help from a Certified Arborist, you can restore your tree’s health.


Other preventative actions you should take include:

  1. Properly watering your trees and making sure your soil drains properly. The soil should be moist (some dry patches are okay) but it shouldn’t be so wet you could make a mud ball.
    • **Our Certified Arborists have observed the importance of not overwatering your trees, especially during the spring. Most irrigation systems don’t need to be turned on around this time of the year. You can hold off on turning them on until later on in the year, when the weather gets hotter and drier.
  2. Keeping your trees healthy overall. Bio-stimulants and proper pruning can boost your tree’s immune system which will lower the likelihood of infection after being exposed to fungal diseases.
  3. In the fall, rake all leaves and dispose of them. This will keep fungal spores in those leaves from being reactivated in the spring.

Need Help With Fungal Tree Diseases?

Editors Note: This post was originally published in 2015 and has been updated for accuracy and comprehensiveness.

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