Prune your Oak Tree before it is too late!

Prune your Oak Tree before it is too late!

Many people ask us, "When can I prune my tree?"  With some trees, it is not as crucial to time pruning perfectly, however with Oak trees it could mean life or death.

If you have an oak tree, it is extremely important to avoid pruning between March (mid-January for large branches) and November.  You may ask, "Why is this so important?"  In Iowa, there is a very infectious fungus that causes a disease called Oak Wilt.  This fungus has been in Iowa for several years and can kill even the oldest tree in less than a few months from infection.  In Iowa, red, black, and pin oak are the most susceptible, however any oak can become infected.

How does the oak become infected?

The fungus can infect a tree in two ways.  The first is through open wounds (fresh cuts) during the growing season (April-September).  A small beetle carries the fungus from an infected tree to the open wound in the healthy tree, which then causes the fungal infection.  The second way the disease is transmitted is through the root system.  If an infected tree is within 50 to 100 feet of a healthy tree, that healthy tree could become infected if the roots are touching.

How do I prevent Oak Wilt?

The easiest way for prevention is by only pruning the tree between Late December until the beginning of February.   If you have very large limbs to cut and the temperatures are seasonably warm, you may consider painting the open wound with a household latex paint to protect the open wound.  Remember, when pruning any tree, it is important to properly clean your tools with alcohol or bleach between cuts.  Pruning during the winter months will give the tree time to heal the wound before the fungus is able to be transmitted.  Another form of prevention is checking your oak trees (if you have several in close proximity).  If you notice you have an oak tree that has brown leaves in early to mid-summer, it may be necessary to form a trench around the tree to avoid the disease from spreading through the root system.


oak wilt

5 Responses

  1. This article talks about trimming during certain months. I have heard to only trim our oak tree if it’s consistently below 45degrees. With such a mild winter we’ve been scared to trim our oak tree. Not only do we love it, it is very large and a lot of large branches hang over our house and garage. Should one consider the temperature when trimming, or just the time of year?

    • Culver's Garden Experts

      Hi Angela! Great question! If you have a very large oak tree, it is best to trim earlier than the end of February. The mild winter is not the major concern, the concern is having the tree heal over the wound before the insects that feed on the fungus become active. The insects are not active in February, however if the trend of warmer temperatures continues, they could become active earlier than normal this year. If you need to do some trimming on large branches over 1″ to 1.5″, it is best to paint the wound (cut) with a household latex paint. This seals the wound, but is not sticky like tree tar that can cause additional insect and disease problems.

  2. I’ve been considering getting my trees trimmed this fall, and I’m glad I didn’t do it before reading your article. Luckily, I don’t live in Iowa, so I don’t think my oak trees are in as much danger of getting the Oak Wilt fungus, but knowing to avoid trimming before November is a really helpful tip and I’ll be sure to schedule accordingly. I’ll see if I can find a tree service that can also check for signs of the wilt and ensure that they know to clean their tools as you suggest.

  3. l

    We live in northern Ohio, and have two small oak trees! One is an Oak and is about 3′ tall. The other is either a red oak or white oak and is about 6′ tall! When should I trim up the lower branches, or shouldn’t i? I have wire fencing around them now to keep the deer from nibbling the new shoots!

    • Culver's Garden Experts

      In Northern Ohio, the best time to prune an Oak would be late December into January.

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