Oak Wilt in Missouri
My History with Oak Wilt
In June of 2022 I was asked to determine why a pin oak tree (left) located in Liberty Park in Sedalia, Missouri was rapidly dying. Once arriving on site, I saw that this tree was defoliating and had large sections of branches that had recently died. There were also several pin oaks across the road from this tree that were dying in the same manor.
After assessing the tree, I went home and did some research and decided that this tree was possibly dying of Oak Wilt. Oak Wilt is a fungus that arrived in the United States in at least the 1940's likely from South America. This fungus affects all trees in the Beech tree family which includes all oak trees. This fungus spreads in two ways; when beetles of the Nitidulid family land on Oak Wilt fungal mats, getting the fungal spores on them and then flying to open wounds in surrounding trees and when the fungus spreads via the intertwined roots of infected and non-infected trees. These are the same two ways that Dutch Elm Disease spread. Once in a tree, the fungus chokes the trees to death by clogging the water moving xylem cells as the fungus feeds on the sugars in the tree.
Oak Wilt infection can only be prevented with fungicide infusions (TexasOakWilt) when applied to trees in the red oak, oak tree sub-family which includes pin oaks, northern red oaks and shingle oaks. Once infection occurs in these red oak trees, they can rapidly die sometimes within a growing season. Oak trees in the white and live oak, oak tree sub-families can be therapeutically and preventatively treated with fungicide infusions. These trees will die over a longer period of time then red oak sub-family trees if they are not treated.
I also need to note that as of right now, trees in the red oak sub-family, bur oaks, and white oaks are known to make fungal mats which can lead to over ground spread by beetles. Due to this, all dead oak trees should be prioritized for rapid removal and grinding of their stumps, so they do not make fungal mats as they die and lead to long distance over ground spread. The basic rule should be immediately removing a dead tree or a tree that is close to death and grind or treat its stump with an herbicide like Garlon 4. Doing this will remove the possibility of fungal mat production and grinding or treating the stump will limit the spread of the fungus through inter-twined roots. Early removal of dead or dying oak trees are our best tool to controlling Oak Wilt Spread.
Oak Wilt Research
During my research about Oak Wilt, I found a website by Kevin Belter, ArborCare & Consulting - Oak Wilt Experts (arborcareandconsulting.com) and that has become the basis of my knowledge of Oak Wilt. I also began to rely on information from the Texas Oak Wilt Partnership ( TexasOakWilt ). Though Oak Wilt was first found in the northern states of the United States, I find the information out of Texas better fits Missouri as we have like thin, rocky soils, and climate.
Based on Kevin's advice on his ArborCare and Consulting site, I took samples from the tree I was first sent to diagnose and shipped the sample to Research Analysis Laboratory, Research Associates Laboratory (vetdna.com) to be properly diagnosed to determine if this tree indeed had Oak Wilt.
This test came back positive as did the ones across the road. I was now off and running to find where else around me were there trees infected with Oak Wilt. This led to a meeting with the Mayor of Sedalia, Andrew Dawson and a speech to the City Council.
At the City Council meeting, the City Council asked the City of Sedalia Tree Board to respond to them about how prevalent Oak Wilt was in Sedalia and what they should do about it. After that I was placed on the Tree Board as the President and worked with the Board to craft the below document.
City Councils Response and Mapping Oak Wilt in Sedalia and S
After spending hours working on the above document and paying hundreds of dollars for DNA tests for City owned trees out of my own pocket, and presenting our letter to Mayor Dawson, he gave it to the Public Work Committe which never did anything about it or ever had a conversation with me or the Tree Board regarding Oak Wilt. The City of Sedalia has essentially stuck their heads in the sand and have made the problem worse by not removing trees that are on their property, were proven to have Oak Wilt, and in some cases are producing fungal mats.
I then quite the Sedalia Tree Board and took it upon myself to send in dozens of more samples in for DNA testing. Most of which came back positive for Oak Wilt. I started to track these cases in a ESRI Survey 123 Form (https://arcg.is/1LyDP80). In 2024, this has become a huge passion project for me as I am currently seeing more mature oak trees in the Sedalia area die from Oak Wilt infection then mature ash trees dying from Emerald Ash Borer. This is scarry to me because the more I learn about Oak Wilt, the more I see that our state agencies and labs like the MU Lab, do not have a good understanding about Oak Wilt.
Misconceptions of Oak Wilt in Missouri
Unfortunately, over the years, I have learned there are so many dangerous misconceptions about Oak Wilt, especially in Missouri. These misconceptions and false information are mainly coming from the Missouri University and their Laboratory. Generally, this information is based on the MU Lab not being able to positively confirm Oak Wilt during their testing process. The lab there uses a cultivation process where they attempt to grow Oak Wilt fungus from samples that are sent in. I assume this process gets many false negatives as Oak Wilt fungus dies at around 90 degrees and I believe the fungus often dies in shipping before the lab receives the samples.
Based on my DNA testing of white oak trees in Missouri, I believe these false negatives have happened to such a degree that MU has labelled white oaks dying of Oak Wilt as White Oak Decline. To solve these issues, DNA testing needs to become the standard of testing for Oak Wilt.
The University of Missouri and its Assistant Extension Professor and Director of the MU Plant Diagnostic Clinic, Ph. D. Peng Tain, has stated publicly at 2024 Pesticide Applicators Recert Program and in this document on Oak Wilt ( oak-wilt-disease.pdf (missouri.edu) ) that " Some companies offer treatment by fungicide for infected trees, but the efficacy of these techniques is subjective and have not been studied clinically, so the results may vary." This statement is false and when I brough up several studies:
Appel, D.N. (1990). The use of propiconazole for control of oak wilt in live oak. Phytopathology 80, 976.
Appel, D.N., Kurdyla, T. (1992). Intravascular injection with propiconazole in live oak for oak wilt control. Plant Disease 76, 1120–1124.
Blaedow, R. A., Juzwik, J., & Barber, B. (2010). Propiconazole distribution and effects on Ceratocystis fagacearum survival in roots of treated red oaks. Phytopathology, 100(10), 979-985.
Juzwik, J., Appel, D. N., Macdonald, W. L., & Burks, S. (2011). Challenges and successes in managing oak wilt in the United States. Plant Disease, 95(8), 888–900.
Wilson, A. D., & Lester, D. G. (1995). Evaluation of propiconazole application methods for control of oak wilt in Texas live oaks. Fungicide and Nematicide Tests, 51, 389.
Dr. Tain wrote me that he would " I will consider your comment and refer to 2-3 forest pathologists from other land grant universities to peer review this publication later this fall." While it is good that Dr. Tain is willing to appeal to peer consensus, it is alarming that no one at MU looked up Oak Wilt Studies on Google and found the Texas Oak Wilt Partnership's website and had seen the numerous Oak Wilt Studies under the research tab before stating the ineffectiveness of a fungicide that was invented in 1979 and has been used in the suppression and control of Oak Wilt since 1990.
Bad information is also being put out by the Missouri Department of Conservation ( Oak Wilt | Missouri Department of Conservation (mo.gov)) , University of Missouri ( oak-wilt-disease.pdf (missouri.edu) ), and Missouri Botanical Garden ( Oak Wilt (missouribotanicalgarden.org) ) which all state that the pruning of oak trees in Missouri should not take place between April and either late June or through July due to this time being the height of Nitidulid beetle activity which cause Oak Wilt over ground spread. All these groups then mention sealing wounds with paint if pruning must occur during this time. While this is decent information, it is not the right information.
Indeed, the height of Nitidulid beetle active is at this time, but these beetles are still active throughout the year and fungal mats on oak trees do form other times during the year outside of the only occurring in spring (nc_2005_ambourn_001.pdf (usda.gov) nc_2005_ambourn_001.pdf (usda.gov)) ( Oak Wilt Fungal Mats | ArborCare & Consulting (arborcareandconsulting.com)).
In my opinion, the right information to pass on it that Oak Wilt fungal mats are present all year long, the beetles that carry Oak Wilt are active all year round, so infection can occur anytime during the year. Due to this painting wounds should occur all year round.
Here is a common example that happens because of the bad information MDC, MU, and the Missouri Botanical Garden put out; tree companies throughout Missouri schedule oak tree pruning in the winter and do not paint cuts. Then because these trees are dormant, the pruning wounds they make do not seal and stay open throughout the dormant season. We then have a hot spell in February or March, beetles wake up and fly, Oak Wilt fungal mats form, and poof, the trees you just opened wounds on throughout the winter are susceptible to infection.
As all Arborist know, the best time to prune trees is in the spring when they are most active and seal wounds the quickest. Based on this, there is a good argument to pruning oaks in the spring and painting them for the best protection from Oak Wilt. Whether this should be the standard is up for debate, but painting wounds all year long is not, it must be done.
What Can We Do
There are many things we can do to address Oak Wilt in Missouri. First, we need to make DNA testing the standard for Oak Wilt diagnosis. We need to alert of Municipal organizations to the presence of Oak Wilt via mapping. We need to have it become a standard to have tree workers paint wounds on oak trees all year long. Fungicide infusion need to be recognized as effective treatments and prevention tools by the University of Missouri and other state agencies. We need to remove dead or dying oak trees and their stumps as soon as possible and state or local should have grants available to help people do this who cannot afford to do it by themselves. We also need to recognize the signs of Oak Wilt infection in specific oak species in Missouri. I will attempt to do this in the final section of this page.