Keep Your Trees Healthy This Spring

Caring for your trees and shrubs is a year-round job. Cool, wet springs and fluctuating temperatures can mean insects and diseases turn your trees and shrubs into their new home or meal.

Our Forestry Section compiled a list of diseases and/or insects that could pose a threat to your landscape throughout the growing season so you know what to watch for.

Bur Oak Blight
A vascular, late-season fungal disease that affects bur oak trees. Multiple infections over several years will weaken the tree, making it susceptible to secondary stressors. Symptoms start in late summer and include: 

  • Purple–brown lesions along the middle vein of the leaf,
  • Wedge-shaped areas of leaf yellowing or dieback, leaves turning brown and curling
  • Dead leaves remaining on the tree through the winter

Oak Wilt
A serious disease threat to oak trees, especially for trees in the red oak family. Watch for:

  • Sudden yellowing or browning of the leaves of entire branches, starting with the leaves at the edge of the tree canopy and progressing toward the inner canopy.
  • Defoliation in the middle of summer

Anthracnose of shade trees
The most common foliar disease affecting a wide range of species. The disease causes leaves to show signs of:

  • Small dead spots on leaves
  • Brown, dead areas along leaf veins
  • Premature defoliation during the summer

Dutch Elm Disease
A vascular fungal disease that affects American elm trees typically starting in late May through the summer months. In summer, trees with Dutch Elm Disease show signs of “wilting” or curling in portions of the canopy, which will eventually spread throughout the entire tree. 

Rhizosphaera Needle Cast and Cytospora Canker
The most common fungal issues impacting spruce trees in our area. Symptoms include:

  • Brownish purple discoloration and eventual death of older needles, while current-year needles show no symptoms
  • Browning needles and dying of branches, beginning with the lower branches and progressing up the tree

Apple Scab
A very common fungal plant disease affecting several different species.  Severe infections will cause premature leaf drop in the summer.  Typically apple scab will not kill the tree; however, multiple infections over a number of years will weaken the tree, making it susceptible to secondary stressors.  Common symptoms will include:

  • Brown to olive, irregular-shaped spots on the leaves in late spring
  • Spots become dark and velvety in appearance
  • Heavily infected leaves may become yellow and fall off the tree from late spring through late summer

Insects that are usually harmless, but can cause severe damage when infestations are heavy, by weakening the stems and leaves. In spring/summer look for:

  • Leaves that are unnaturally curled inward
  • Black sooty mold on leaf surfaces
  • Sticky substances on sidewalks, driveways, or vehicles

Two-lined Chestnut borer 
TLCB is a common insect that can cause oak mortality over several years if the infestation level is high. The insect is attracted to stressed and weakened oak trees.  Signs to look for are:

  • Leaf browning and twig/branch dieback.
  • Branches in the upper canopy have a wilted look while the lower canopy is still green.
  • “D” shaped exit holes in the trunk of the tree (close to the base).

Consult a Certified Arborist if you recognize any of the above-listed symptoms or see other changes to your trees or landscaping throughout the year.

The City's Forestry Section would be happy to set up an appointment to meet on-site and discuss any of your plant health care concerns. Also, please remember that an ounce of prevention is worth a pound of cure. Regular watering, fertilizing, fungicide, and insecticide applications can help keep insects and diseases at bay and play an important role in maintaining a healthy tree or shrub.

For a more detailed description of the above-listed diseases and insects, please visit the Morton Arboretum website.

Stay Informed!