‘Tis the Season – the ONLY Season – When It’s Safe to Prune Your Oaks!

(Click on photos to enlarge; hover cursor for captions.)

Notice something odd about the three photos above? Right. They all show dead trees. And it turns out they are all Michigan oaks – in a neighborhood, in a park and in a natural area. Oak Wilt, an invasive fungus deadly to oaks, has killed these mighty giants in Minnesota, Wisconsin and throughout Michigan, including Oakland County. Researchers like Dr. Monique Sakalidis at Michigan State are working to more thoroughly understand oak wilt and how to prevent it because at the moment, there is no cure once a red oak is infected. The good news is that most new infections can be prevented by not damaging or pruning oaks during warm weather (April to October). So we all need to know how to protect our oaks!

The Oakland County CISMA (Cooperative Invasive Species Management Area) arranged a workshop with Oak Wilt specialist, Julie Stachecki, who is also an ISA certified arborist (International Society of Arboriculture) and President of the Arboriculture Society of Michigan. She packed a lot of information into her two hour presentation! We learned how this dangerous fungus is spread and how to protect the oaks of Oakland Township. Here are some important basics and links to more detailed information. (All of the photos in this blog were taken by Julie Stachecki, except the one on the left above by Dr. Dave Roberts and two photos of oak leaves below by Cam Mannino.)

The Danger is Real…and Some of the Photos Aren’t Pretty

Oak wilt is caused by an exotic fungus (Bretziella fagacearum) that likely arrived in North America around 1900. Oak wilt can kill a tree in the Red Oak group (northern red oak, pin oak, black oak, and scarlet oak) in 6-8 weeks! Species in the White Oak group (bur oak, post oak, white oak, and swamp white oak) can also be infected but may survive, or just die more slowly. Red oaks have bristles at the tips of the leaf lobes, while white oaks have rounded lobes with no bristle. There is currently no cure for oak wilt, so prevention is crucial! Don’t injure your oak trees between March and October!

Overland Spread by Beetles

The oak wilt fungus is spread by native sap beetles (fam. Nitidulidae) that are attracted by the scent of any wound on an oak tree – for example, those caused by lawnmowers, pruning or broken limbs. These beetles can spread the fungus several miles in one year!

The beetles can arrive within 10 minutes of wounding! So prevention is critical. When wounds occur, sealing them with a pruning sealant or latex paint needs to happen quickly. The beetles are active from mid-March through October, but there are greater numbers of them from mid-March to July.

If the beetles have been feeding on the oak wilt fungus in an infected tree, they can carry the fungal spores to nearby healthy but wounded trees. Once they land on a wound with the spores on their bodies, a red oak tree will die in 6-8 weeks.

Local Spread through the Roots

Oak wilt can also spread to healthy trees through the roots of infected oaks.  Oak trees, particularly red oaks,  are connected underground by root grafts even if they are as much as 100 feet apart. The fungus will keep spreading throughout the root systems and can kill every oak tree in a neighborhood, park or forest until the root connections run out or are professionally severed

How to Protect Your Trees

Prevention is the key to protecting your oak trees. Don’t prune or injure your oak trees between March and October! Only prune oak trees between November and February (late fall or winter).

  • If the bark of your oak tree is injured in any way (e.g. by lawnmower, pruning in the growing season, wind damage) from March to October, immediately seal the wound with tree wound paint, latex paint, or clear shellac. That should keep beetles from landing on exposed tissue and protect your trees. If you can’t reach the area, call an Oak Wilt specialist.  (See below.)
  • DO NOT MOVE FIREWOOD.  It’s one of the significant ways in which oak wilt spreads.
  • An Oak Wilt Qualified Specialist can’t save your tree once infected,  but he or she can take measures to try to protect the oak trees nearby.  See the contact information for the Michigan Oak Wilt Coalition below.
  • Avoid using tree crews that are not qualified as oak wilt specialists. Confirm any diagnosis of oak wilt with an expert. Many different stresses and less lethal pests can cause symptoms of concern on oak trees. You don’t want to make treatments or cut down a tree unnecessarily.

Signs of Oak Wilt Infection

Fallen leaves from an Oak Wilt-infected tree in mid-summer. (J. Stachecki)

In June, July or August, leaves discolor to a dull olive green or turn partially brown, often near the top of the tree first. Discolored leaves then wilt from the top of the tree downward and additional leaves become brown or bronzed. Rapid leaf drop occurs as the disease progresses.  Fallen leaves are usually brown at the tips and margins and sometimes green at the base. (See photo above.)

The year after a tree is killed by oak wilt (but sometimes that fall), fungal pressure pads may form beneath the bark of the tree. The growing pressure pad pushes on the bark above it, often forming small cracks that allow beetles to access the fungus.

If You Think You Have an Oak Wilt Infected Tree:

  • Confirm any suspicion of oak wilt with an expert. Dead leaves aren’t enough since other diseases can cause similar symptoms.
  • Don’t Cut it Down Yourself!  You may make the problem worse by forcing the fungus more quickly into the roots, infecting nearby oak trees with the oak wilt fungus.
  • Again, contact an Oak Wilt Qualified Specialist.  Don’t be tempted to use just any arborist or tree service.  Specialists have passed an exam on identification and management of Oak Wilt and are required to be either an ISA Certified Arborist, Certified Forester or have a 4 year degree in a related field.  They can  provide you with the best way to protect other oaks in your yard, your neighbors’ yards, or a forest or park nearby from this deadly fungus. Management options may include tree removal, tightly covering infected firewood piles, preventative injections of nearby non-symptomatic trees, and trenching around infected trees to prevent spread through the roots to nearby trees.

Keeping the “Oak” in “Oakland”

We all know that we want to preserve the oaks for which Oakland Township and Oakland County were named. To do so, we need to take the Oak Wilt threat seriously and work as a community to prevent its spread. Even one infected tree with oaks nearby can spread and kill all the trees connected to its roots. That could potentially affect whole neighborhoods, whole parks, whole forests. So the first step is to educate ourselves and our neighbors so that we can act quickly. First, prevent any injury to oak trees between March and October. Second, immediately seal any wounds that do occur between March to October. Finally, if you suspect a tree with oak wilt, quickly hire experts to confirm the oak wilt diagnosis and to keep the infection from spreading.  So please read the information on the Michigan Oak Wilt website and tell your neighbors about how to prevent the spread of oak wilt!  We can do this!

Many thanks to Julie Stachecki of the Michigan Oak Wilt Coalition for generously sharing her photos and her time.

Resources for More Information and Help:

  • Website of the Michigan Oak Wilt Coalition for more detailed information and to find an Oak Wilt certified specialist arborist: michiganoakwilt.org
  • For reporting suspected cases of Oak Wilt: email DNR-FRD-Forest-Health@michigan.gov
  • Midwest Invasive Species Information Network: http://www.misin.msu.edu

2 thoughts on “‘Tis the Season – the ONLY Season – When It’s Safe to Prune Your Oaks!

  1. +Oh, Camie, We are surrounded by Oaks (as well as firs.) As soon as I heard about Oak wilt (1 1/2 years ago), I contacted our Forestry gal, and she reassured me it hadn’t reached Presque Isle County yet. I thank you for the info on how to avoid and what to do if one notices open wounds. It breaks my heart of see these quiet, magnificent giants in jeopardy. The quickness of their demise is astounding. Val was very anxious about this before he died, even when I tried to reassure him. Thanks for this timely article, and the photos are a huge help. gerre

    1. Gerre, I’m so glad you already know about Oak Wilt and are keeping an eye on your trees. Our yard and the slope below us are covered in black oaks (a member of the red oak family), so I’m really glad to know about it,too. I’m happy too that the photos from Julie Stachecki are helpful. Oak Wilt is such a serious danger to our Michigan oaks that I hope people are willing to prune in the winter and cover any wounds immediately in the summer months. I do a lot of the mowing here, and I know I’ll be even more careful in the future! I’m hoping to get my neighbors some info on this as well to protect all the oaks in our neighborhood and the parks since it spreads so far and fast to other oaks! Thanks for the kind comment.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s