Other Tree Pests & Diseases

Elm and Dutch Elm Disease (DED)

The stately elm tree was once a staple of the community forest. Now, due largely to Dutch elm disease, elm trees are a rare sight. Dutch elm disease (DED) is a fungal disease that has devastated native elms in Minnesota beginning in the 1960s, and is still a problem for the few elms that remain today. Native elms susceptible to this disease include the American elm, rock elm, and the red elm (also known as the slippery elm). Siberian elms, which are common throughout Fridley, are less susceptible to the DED. New disease-resistant elms are also being tested and planted to reintroduce this valuable tree into our community forests.

Symptoms of DED include wilting leaves that turn yellow then brown, often beginning in late spring/early summer but may be seen throughout the growing season. This can affect one or more branches on the tree. Leaves may also fall off of the tree prematurely.

Many other tree problems can resemble DED. 
Click here to find out more about how to identify Dutch elm disease in your trees.

Oak and Oak Wilt or Bur Oak Blight

As part of the Anoka Sand Plain, Fridley is lucky to have many native oak trees throughout the city. Unfortunately, oak trees have their share of maladies that can affect their health and growth. These include oak wilt and bur oak blight.

Oak wilt

is a disease caused by a fungus that can be spread in two different ways: 
  1. Insects: sap beetles spread the fungus by feeding on infected trees, then feeding on healthy trees. They are attracted to the smell of the sap produced by pruning cuts and wounds.
  2. Root grafts: roots of an infected tree can grow together with the roots of other nearby trees, spreading the fungus. Healthy trees can be affected by root grafts from infected trees more than 30 feet away.

Oaks in the red oak group are impacted the worst by this disease. Oaks in this group can be identified by the sharp points on the tips of their leaves, and include red oak and pin oak. Symptoms of oak wilt for this group include rapid wilting of leaves, beginning in the upper and/or outer part of the crown of the tree. Leaves turn reddish brown and fall off of the tree prematurely. This disease can kill a red oak in less than one growing season.

Oaks in the white oak group are less severely impacted by oak wilt. Oaks in this group can be identified by the rounded lobes on their leaves, and include bur oak, white oak, and swamp white oak. Symptoms of oak wilt for this group include gradual wilting of leaves on one or more branches, and leaves will turn reddish brown. This disease will take several years to kill oaks in the white oak group.

Oak wilt prevention tip:

don’t prune oak trees from April through mid-July! The scent produced from a fresh cut on an oak tree can attract a fungus-carrying beetle to the tree. If a wound is unavoidable, immediately (within 15 minutes) apply a coat of paint or shellac to the wound to deter visits from these insects. This is the only situation where applying paint to tree wounds is recommended. 
Click here for more information on oak wilt, including identification and prevention.

Bur oak blight (BOB)

is a leaf blight disease that only affects bur oak trees. Symptoms include yellow or brown wedge-shaped areas towards the top of the leaf. Dead leaves will often hang on the tree throughout the winter.

Bur oak blight will only kill the tree if it experiences severe infection over several years. Otherwise, the main concern with BOB is aesthetic.