Oak wilt risk status in Minnesota

Q. What is oak wilt?
Oak wilt is a fungal disease that kills thousands of oak trees every year. Oak wilt spreads in two ways: Through root grafts between similar species, radiating outward from a central infected tree; and over land, carried by oak sap beetles carrying fungal spores from tree to tree.

Q.  What are the “risk season” references?
A.  There are three risk season timeframes: High Risk, Low Risk and Safe.  They refer to the probability that oak wilt will infect a tree. Specific dates for timeframes vary depending on weather conditions.

High Risk months in Minnesota are typically April, May and June.
Low Risk
months are March, July, August, September and October.
Safe
months are November, December, January, February and March.

Q.  What are these probabilities or “risks” based on?
A.  Three criteria are considered.  First, is the fungus that actually causes the disease active?  Second, is the beetle that carries the fungus to the oak active?  Third, is there oak wilt in the area?  If all three criteria are met, then the transmission of oak wilt from one area to another is very likely.  This is referred to as “over-land transmission” of oak wilt.

Q.  What are the best ways to either avoid or minimize the probability of oak wilt infection?
A.  First, avoid any wounding during the High Risk (and hopefully, the Low Risk) period…no pruning, no construction activities near the oaks.  If a tree is wounded, seal the wound quickly (within 15 minutes) with one coat of shellac (preferable) or a water-based paint.  If oak wilt is in the area, it’s the High Risk season, and the wounding is unattended for more than 15 minutes, the probability of infection rises dramatically.

Second, and especially important if oak wilt is established in an oak woodland, prevent the spread of the pathogen through root grafts by cutting through the connecting roots using a vibratory plow.  This will need to be done by a professional, preferably a Certified Arborist and if done correctly is a very reliable technique to reduce the amount of oak wilt spread.

Thirdinjection of a chemical fungicide may reduce the risk of oak wilt-related tree mortality from root graft infections for 2-3 years. If combined with vibratory plowing, chemical treatment may provide long-term protection. This should only be done by a trusted and experienced professional that is licensed to apply pesticides and ideally is a Certified Arborist.

Fourth, do not move firewood from oaks that have died from oak wilt off of or on to the property in question.  The red oak group in particular harbors the fungus for several months under their bark, even if they’ve been cut down.  Unless the bark of oak wilt-killed oaks has been removed, that firewood needs to be used on site (burn before the next High Risk period) or covered completely.  If the wood with the bark on is tarped, the tarp must be at least 4 mil. thick and preferably clear in color.  The tarp should be weighted down at the ground line and sealed with soil at the ground line so no beetles can crawl in and out.  Keep the wood covered for at least one full year after the tree has died.

Q.  Can any beetle move the fungus from one area with oak wilt to another?
A.  The nitidulid beetles that move oak wilt are commonly called “sap-feeding beetles.”  There are only a couple of these types in Minnesota and they’re very small.

Q.  Can an oak become infected during the Low Risk or Safe periods in Minnesota?
A.  Oaks can become infected during the Low Risk period, but the probability is very low.  However, since it could happen, it’s best to delay pruning of the oaks until the Safe period or to quickly seal the pruning wounds with shellac or paint to avoid attracting the beetle if pruning during the Low Risk period is unavoidable.  During the Safe period, there is virtually no risk that an oak can become infected with oak wilt by over-land transmission of the fungus.

Q.  Is “over-land” transmission the only way oaks can become infected with oak wilt?
A.  No.  Most oak wilt is spread via root grafts.  Oaks of similar species, for instance red oaks, can root graft with other oaks nearby…easily within 60-80 feet of mature oaks.  When this happens, fluids can pass from one oak to another, including fluids that carry the fungal pathogen.  Oak wilt spreads from one area to another (distances greater than a quarter mile or more) via the beetles carrying the fungus.  Once the disease is established in a tree, it spreads from that tree to others via root grafts.

Q.  Are all oaks affected the same way?
A.  The red oak group (red, black, Eastern pin, northern pin and scarlet) are more seriously affected by the disease-causing pathogen.  Once infected, they do not recover and die very quickly, often within 4-6 weeks of infection during the growing season.  The white oak group (bur, white, bicolor) can become infected, but they often live with the disease for a long time before dying.  This lengthy period allows tree care professionals to intervene, even after infection, and can often save the trees.

Q.  Once the tree becomes infected, is there any treatment?
A.  For oaks in the red oak group, no.  For oaks in the white oak group, yes.  A qualified tree care professional will prune out the dead wood (if the disease hasn’t progressed too far) and if licensed, inject the tree with a systemic fungicide.  In most cases, the trees will recover if there are no other health problems affecting them.

Q.  In areas where oak wilt has killed the oaks, should replacements be other than oaks?
A.  Genetic diversity is always a good way to make a forest, woodland or landscape healthier.  Few insects or disease-causing pathogens kill wide varieties of trees.  If the area that suffered oak wilt losses is dominated by oaks, replant with other species such as sugar maples, black cherries, hackberries, white or river birches or maybe some of the disease-resistant American elms.  If oaks didn’t dominate the landscape (made up less than 10% of the tree population), some of the replacements can be oaks, especially those in the white oak group.

Q.  Is there any other resource that can provide more detailed information and pictures of oak wilt?
A.  The publication “Oak Wilt in Minnesota” by David French and Jennifer Juzwik is probably the best available resource.  Additionally, the Minnesota Department of Natural Resources web site has very valuable oak wilt information, and the University of Wisconsin Extension has an excellent short publication called Oak Wilt Management: What Are the Options?

Q.  Can I add the University of Minnesota oak wilt widget to my site?
A. Yes!  You can download the embed code here.

MyMinnesotaWoods
The University of Minnesota Extension Forestry team.

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130 Comments

  1. I’m leaving town today or tomorrow for a week.

    I’ve noticed a lot of little branches a foot or less — coming off the huge oak tree in my back yard. I do not see any bugs or disease. The ends look almost like they were cut off, rather than fell off. Perhaps the squirrels?

    what do I do? thank you!

    1. Hi Krysta. Not much that you can or should do. You’re probably right that squirrels are cutting and dropping the branches. If you’re in a high-risk area for oak wilt, there’s always a chance of transmission, with or without wounds. And there’s not much you can do to keep squirrels out of an oak tree. Cross your fingers and enjoy the trip!
      -eli

  2. Hi. After raking my yard this spring, I have developed a persistent cough, and an inexplicable nose bleed. Is it possible that I have contracted oak wilt?

    Thanks,

    Jason

    1. Hmmm… First we need to know for sure whether you’re an oak. Are you ring porous or diffuse porous?

  3. Hi Jason,
    The administrator took your question for a joke, I think. Just in case you weren’t joking, however, here’s my input. Oak wilt is caused by a fungus, and I suppose it would be possible to have a reaction to the fungus if you have a sensitivity to fungi, but it seems very unlikely that you would since the spores do not become airborne in the sense that they can be readily inhaled. I would ask a doctor though, not a forest health forum.

  4. How far north and northeast in MN is oak wilt considered a threat? I work on the Superior National Forest, and may need to core northern red oak this summer…should I wait until fall to sample stands that have oak? Thanks for any feedback!

  5. A certified arborist just diagnosed 3 large red oaks with wilt, on front of my lot. One person suggested breaking the root graphs with vibratory plow or trencher, but I am getting conflicting messages on depth. One person says 20 inches, another 5 Feet!. What do you say?
    thanks

    1. Hi Peter.

      Here’s an excerpt from the Forest Service’s “How to Identify, Prevent, and Control Oak Wilt“:

      Trenching and vibratory plowing
      Cutting roots by using a trenching or cutting tool effectively controls the expansion of oak wilt pockets. In the Lake States, using a vibratory plow with a five-foot blade is the most common method of disrupting grafted root systems. The vibratory plow consists of a mechanical shaker unit with an attached blade that is pulled behind a tractor. The blade penetrates to a depth of about 5 feet, and cuts through the roots of oaks that may be grafted together. While oak roots may extend deeper than 5 feet in the soil, most root grafts are disrupted by trenching or plowing to that depth.

      The same paragraph goes on to note that if other trenching equipment is used, the trench depth should be at least 3 feet.
      -eli

  6. I have what I believe is a Bur Oak that has been wilting now for a couple of summers. We moved in to our current house in July of last year and found that many of the few remaining branches on this heavily pruned tree had dried / wilted leaves. Then, this spring, some of those brances seemed to be fine, producing healthy looking leaves. Now, in early June, the leaves on those branches are again starting to wither. I had an “arborist” come to the house, and he sent me a quote to remove the tree without explaination. Based on the information from this site, I do not believe this is oak wilt as the tree is NOT wilting from the crown down, and individual leaves seem to either be wilted or not (not progressing from the tip). I cannot see obvious signs of infestation or damage. Do you have any advice for next steps for a home owner that would like to save his tree?

    Thanks,
    Steve

    “The trees wilt from the top of the crown down and individual leaves wilt from leaf tip and margins to the bases, turning bronze to brown”

  7. Eli,

    Yes, the article you linked to seems to describe exactly the problem we have with our oak. The tree seems to start the season fine, but by June many of hte leaves on most of the branches look like the picture in the article. There doesn’t seem to be a difninitive suggestion on how to treat this problem; would you recommend bringing someone out to treat the tree with a fungicide?

    Thanks,
    Steve

  8. I have white and red oaks on my property in burnsville. In the last few years I have lost a total of 15 red oaks to oak wilt but the largest of my trees – the white oaks – appear to be surviving fine. Each year i have waited until the fall to have the trees removed professionally and taken off the property. I suspect that the root grafts are causing the spread to otherwise healthy, undamaged trees. My question is – are the white oaks also prone to root graft spread from the red oaks. The two large white oaks i am concerned about are close to a couple of red oaks that have died this spring/summer.

    thanks,
    Todd

    1. Hi Todd. Species of the white oak group, which includes bur oak, are less susceptible to oak wilt than species of the red oak group (red, scarlet, pin, and others). Symptoms sometimes take longer to appear in white and bur oaks than in red.

      As for root grafting, the following text, quoted from a Wisconsin DNR page called Oak Wilt in Wisconsin, addresses your question:

      How does this disease spread?
      Underground
      Most oak wilt moves from diseased trees to healthy trees through roots that have become interconnected (root grafts). Most root grafts form between oaks of the same species; red oak roots graft more commonly than do white oak roots, and grafts between red and white oaks are very rare.

      (Source: Wisconsin DNR)
      -eli

  9. Thanks for that information – I am glad to hear it.

    Now my next question – i have these three red oaks that are dead from oak wilt this spring/summer. In the interest of saving the others nearby, do i remove the dead ones now or do i wait until November.

    thanks again – this site and the forum are excellent resources!

  10. A storm rolled through last night, breaking off a large branch of one of my red oak trees. Since I missed the ’15 minute’ window, would anything be gained by painting the wound today?

    1. Jim: Gary Johnson has a great publication called Storm Damage to Landscape Trees: Prediction, prevention, treatment. This excerpt answers your question:

      Wound Repair: ….When pruning branches or repairing wounds, it is usually unnecessary to paint the wounds. The exception is during oak wilt season (April, May, June). During this period, wounds made on oaks should be painted immediately with a latex paint or shellac to deter insects carrying the oak wilt disease fungus.

      Minnesota’s high-risk period for this year has now passed, so there’s no need to paint over the wound.

  11. The ends of the branches from my big white oak are being cut by the squirrels and are all around the base of the tree. I keep removing them but there is always more. Why do they do this and also is this in any way bad for the survival of the tree. Thank you.

    PS I live in the New York City suburbs,

    1. Hi Don. I know how you feel–the volume of branches on the ground can seem quite alarming, but squirrels have been nipping oak branches since the dawn of time, and the trees seem to pull through. There’s really no cause for concern.
      -eli

  12. I trimmed some oaks and actually removed some unwanted oak trees the last week of January. I understand this is the “no risk” period. Should I do anything else – such as sealing the wounds?

    Thanks

  13. Hi Rob. There’s no need to seal the wounds or take other action as long as your work was done during the no risk period, and the end of January is about the best time to do it–right in the middle of the no-risk period. This is covered briefly in the fourth question above.
    -eli

  14. Is it too late to trim Oaks this year. I wanted to have it done but the two companies I talked too have said they would wait 2 weeks so the ground is drier and the trucks won’t leave ruts. I am concerned that the trees will then be more susceptible to oak wilt. Thanks.

    1. It’s not too late now, but in two weeks it may be. Obviously rutting would be a concern now, and with the late spring (as of late March) there’s a chance that the high risk period may begin late, but normally it begins in early April. So you may be in a tight spot, unfortunately. You can always see the current risk status on this page and our homepage.

  15. My neighbor is having a white oak tree that died several years ago removed today. The cause of death of the tree is unknown. Not all the wood will be taken away. Their property and ours both have multiple red and white oaks. Should we be concerned? Are there any precautions we should take or ask our neighbor to undertake? We live in the Twin Cities.

  16. We just bought a house and the home insurance company is requiring us to trim our red oak tree or they are going to cancel our policy. We are worried about trimming it at this time since it is a high risk time for oak wilt and 2 tree companies have recommended not trimming it. Is there a way to fight this with the insurancance company, or can they demand this even though the risk loss of the tree is high? We live in the Twin Cities.

  17. Alison-

    There is a chance your neighbor’s white oak died from oak wilt. You DO NOT need to be concerned about your neighbor’s wood because the tree has been dead for several years which is a sufficient amount of time for the tree to dry out (killing the fungus).

    You might first want to think about how quickly the neighbor’s oak tree declined because if it died fairly quickly, it did not have oak wilt. If it died from oak wilt, its decline would have been over several years. (This only applies to white oaks and bur oaks)

    If you highly value your own oak trees (white and red), you DO need to be concerned about your trees IF there may be oak wilt in your neighborhood. You will want to think about which trees you value and whether it is worth it to you to treat them with a preventative fungicide (Alamo).

    -emily

    U of M Forest Extension & Outreach
    treeinfo@umn.edu

  18. I have a red oak that has oak wilt. There are several red oaks within 50- 100 ft. of this tree. I have been told by one person that it needs to be removed immediately. Another person said to wait until winter to remove it because the disease may be pulled into the healthy trees faster through root grafts if removed now in August. There are several utility lines underground so trenching is not an option.

  19. Hi Jed. Trenching is by far the most effective way to prevent transmission from the infected tree to other nearby trees. Without trenching, the surrounding red oaks are very likely to become infected as well. As noted above, these other trees can be treated with a systemic fungicide that may provide some protection (see “What are the best ways to either avoid or minimize the risk…?” above.
    -eli

  20. We have a very large Oak in our Front Yard. (I am pretty sure it is a white oak, but am not sure).

    We have noticed the leaves are starting to wilt, look sickly, and die much sooner than any other oak in our yard or our neighbors yard. All of the Oaks in the neigborhood look fine.

    When is the best time to have the tree inspected? Now while the leaves are dying? Or do we wait until next year to see if the leaves come back.

    Our neighbor just had a pine removed from her yard (about 50 to 75 feet away) due to disease, but I don’t know what it was.

    Also who do we contact to have the tree inspected?

    Thank you so much!

    Jeff Bradberry

    1. Hi Jeff. Sorry to hear about your tree. In addition to reading the text on this page, you might consult this post about Bur Oak Blight (BOB) in Minnesota, as well as this Bur Oak Blight fact sheet from May 2011. It’s possible that you’re seeing signs of BOB. If so, the first link includes instructions on how to submit a sample to the UMN Plant Disease Clinic. Either way, now is the time to collect leaves. I would strongly suggest taking a quality close-up photo showing typical infected leaves, as the appearance of the leaves may change rather quickly after removal from the tree.

      If you do have oak wilt, your chances of saving the tree are much better if you’re correct that it’s a member of the white oak group. White oaks (including bur, white, swamp white, and others) have leaves with rounded lobes rather than pointed. As for an on-site inspection, your best source would be a local ISA-certified arborist. You can find a searchable database of ISA-certified arborists here.
      -eli

  21. Since trenching is not an option, when is the best time to remove the infected tree? Now or during the dormant season? I have been told by one person that it needs to be removed immediately. Another person said to wait until winter to remove it because the disease may be pulled into the healthy trees faster through root grafts if removed now in August. The cost of fungicide treatments are too much for me to take on now. I understand that the other trees are in jeopardy but am curious as to the best timing of removal of the diseased tree because of the conflicting info I am getting from arborists.

  22. Is fertilzing your yard and keeping your yard watered durung dry spells help with the health of oaks and help them keep the oak wilt away?

    1. Hi Gary. Yes and no. Drought can weaken trees, making them more vulnerable to bugs that are otherwise harmless, like two-lined chestnut borer. Watering can help to keep trees vigorous and resilient. But watering won’t protect your trees from oak wilt. Red oaks are not resistant to oak wilt, with or without adequate water.
      -eli

  23. Are we really still in the safe time in southern Mn this year? The exceptionally warm weather hasn’t moved the High Risk time up?

    1. Hi Pete. The nitidulid beetles that transmit fungal spores from tree to tree are not yet active. This is the primary factor affecting the start of the high-risk period. We’re keeping an eye on conditions this spring and will update the risk status as soon as risk factors increase. Thanks for the question.
      -eli

  24. If I have pin oak trees already down from a windstorm last year, do I have any concerns if I cut them now? They’re either down or leaning on another tree. I probably won’t touch the one tht is leaning. Thanks for a response.

    1. Hi Jim. If the trees that are already down are completely dead, the risk would be less than if there’s still living wood. It’s not uncommon for downed trees that have a small portion of the root mass still under soil to continue to put out at least a few new leaves. If that’s the case, I’d be cautious. If the trees are completely dead and dried, your risk would be less.
      -eli

  25. Been doing alot of searching, here’s the question. Is it ok to grind out the stumps in April. Have 25 stumps from last winter and 5 more from about 4 weeks ago.

    1. Hi Tom. The issue is that the nitidulid beetles that carry the oak wilt pathogen (fungus) are attracted to the scent of freshly cut oak. Grinding the stumps of trees that wer cut either 6-8 months ago or 1-month ago would stir up enough fresh-cut wood that I’d avoid it if possible until late summer when the risk is lower. There’s no way to know for sure what will happen, but grinding the stumps now would be a risk I’d personally want to avoid if possible.
      -eli

  26. Yesterday I had to cut down a red oak that would have fallen on my garage. Can oak wilt infect the stump? What can I do to the stump to prevent infecting the other trees, as I was just going to cut it flush with the ground. Does killing the stump with brush killer help prevent the spread, or does that matter? Can I seal it with paint or something?

  27. About 40 years ago I planted an acorn with a little growth on it. Today I have a large & beautiful oak tree. I do not know the variety. Early this spring it produced little green seeds. We had a hard freeze and the seeds turned brown. Now there are just a few leaves coming. Did the hard freeze cause this condition? Will the tree recover?

    1. Hi Frances. Most trees can grow through damage from an early season freeze or, for that matter, a nearly complete mid-season defoliation event. The recent rains should leave the tree in a good condition to grow through it. After the very early warm weather and a very early flush on many trees, plant and tree development slowed down a fair bit and just kind of lingered through a few weeks of cooler weather, which may explain why you haven’t seen many leaves coming in. I’d wait a bit and, as long as there are no other problems with the tree it should be fine. Good luck!
      -eli

  28. I haven’t seen this mentioned in the forum but I have now lost 2 Red Oaks and have started treating several White oaks for two-lined chestnut borer. At first I thought the whites had oak wilt but an arborist identified the chestnut borer as the culprit. I then lost a Red Oak nearby and again I thought it was Oak Wilt because of the way the crown changed color was very much like previous trees in my area that died from oak wilt. However the leaves didn’t fall off the tree very quickly and when the tree company removed the tree it was determined that it was not oak wilt. However we did not see the obvious d-shaped holes in the branches where the borer larvae exit either so this loss is still a mystery though this still seems to be the arborist consensus. Just wanted to mention that there are other factors besides the oak wilt fungus that can attack the oaks. BTW we hear a lot about the emerald ash borer but not much about the two-lined chestnut borer because it is not considered an invasive species.
    Thanks
    Wayne

  29. My neighbor is cutting down his tree that I know died of Oak Wilt. I tried to explain that May is the worst time to cut it down, but he won’t listen to me. Is there any law I could point him to to help him understand that he is putting our entire neighborhood at risk? There are probably 10 oaks connected to this one tree (in close proximity). Is there anyway to protect my trees when they are less than 50 feet away?

  30. Thanks Wayne for the comment. Two-lined chestnut borers are native and are generally secondary pests, meaning that they tend to attack trees already stressed from wounding, drought, or other factors. A good source for more information about TLCB is the Forest Service’s TLCB Forest Insect & Disease Leaflet.
    -eli

  31. I have a fair amount of oak wilt on my 23 acre parcel, with several trees standing dead. How long after a tree has died does it remain a contaminant for other trees? If it is standing dead for at least a year, is it still a contaminant? If the dead (for more than one year) tree has broken off or fallen down (uprooting the root system), is it still a contaminant?

  32. John,
    Spore mats, which are the structures that produce the spores that are picked up and carried by beetles to fresh oak wounds, are generally produced within one year of the tree’s death. However, the root systems of trees killed by oak wilt can survive for 5 or more years, and can continue to harbor the fungus that causes oak wilt. Removing trees that died last year only removes the risk of insect-vectored transmission of oak wilt, it does not remove the risk of below-ground transmission via root grafts. If the tree has been uprooted, the risk is reduced but it is possible that the fungus can survive in remant portions of the root system not disrupted. Risk of transmission will decrease over time, but if it has only been a few years since the tree(s) died of oak wilt, you may want to consider taking measures to protect your remaining trees.

    1. Ryan –

      Once the tree has been dead for more than one year, is there a continuing risk of contamination from cutting the trunk and branches for firewood? I assume from your answer above that the risk of insect-vectored transmission is greatly lessened. Also, at present, I only burn the dead tree firewood on the property where the tree death occurred. Is there a risk attached to transporting the (dead for more than one year) firewood to another property?

  33. John,
    There is no risk of spreading the disease by cutting wood from a tree that has been killed by oak wilt. I would only caution you to sterilize your saw before cutting/pruning healthy oaks afterwards becuase it is possible to spread the fungus on contaminated tools. Rubbing alcohol in a spray bottle would be just fine for this purpose. If the wood has been dead for more than a year, there is little risk of spreading oak wilt if you transport the firewood. Be aware however that movement of hardwood firewood is restricted out of Hennepin, Ramsey, Winona, and Houston counties because of Emerald Ash Borer quarantines. Also, while the risk of transporting oak wilt on aged firewood is very low, we always recommend utilizing local firewood if possible to reduce the risk of spreading other insects and diseases.

  34. We live in Mpls and have a cabin in Amery WI. We have 4 oaks that have dead branches directly above our deck and I have been very concerned wth safety as we sit there. I now have a tree trimmer lined up to trim only the dead branches. He only does residential on weekends and it has snowed the last two weekends! Since he climbs the trees, needless to say, it’s been too dangerous. He is planning on this Saturday morning. I am watching the temps and am concerned that we will be in the high risk time by then. He promises to get there by 7 am before it warms up and has agreed to spray the larger limbs asap. (Why not the smaller ones, I need to ask him!) What do YOU recommend? If the branches are dead, is the risk still high? Help! Thank you. S

  35. We just had a large red oak split by the wind last night. A large portion fell on our second garage. Today we have had it cut up and pulled off the roof, but the section that is still standing is splintered on one side. Since the date is June 22, I assume we are still in high risk time. There was no way to seal the tree during the night and storm, or even now because of the splintering 12′ up. There was no wilt in this tree or on our own property now. We had plowing done years ago. There is still some further away in the neighborhood (Anoka County). Is the wood from this tree at risk of attracting the bugs and is there any way it would be a danger to our other trees? We will probably have to remove the remaining part of the tree since there is split down the middle of the trunk. Should we be concerned about whether infection could start and go into the roots? Would stump grinding stop it?

  36. After this huge storm last Friday, I saw some pieces of bark on the ground. A couple and not more than a foot in length. I looked for where so I could seal it (though even if I had, it would’ve been too late by the time I saw it) but couldn’t f ind it.

    Now what do I do. This is a gorgeous 200+ year oak. I don’t know which kind it is. Do I try to do a preventative fungicide just in case?

    1. Hi Krysta. I would not worry about trying to seal up the areas that lost their bark. Anything that was going to get in to the tree through the new wounds will be in there by now. As for whether or not the fungicide treatment would be advised, that is up to you based on how important the tree is to you. Based on the article linked above addressing the fungicide issue, a propaconizole treatment would be expected to protect the tree for 2-3 years, after which another treatment would be needed. As the fungus does seem to remain alive in the roots of the tree, treatments would be needed every few years if the tree is indeed infected.

  37. I had a red oak die in the fall of 2011. I thought it was oak wilt but was told it wasn’t. Summer of 2012 that tree was taken down. This week a tree about 20 feet from that one has dropped most of it’s leaves I’m sure it’s oak wilt, and have three more large red oaks within 20, 30 and 40 feet, is it to late to cut the roots on these others?

    1. Hi Rich. It’s generally recommended to create primary and secondary barriers (root trench treatments) not only immediately around infected trees, but also on the far side of nearby asymptomatic trees. A few resources that explain this in more detail, including graphics with recommended trench locations: How to identify, prevent, and control oak wilt (USFS), Oak wilt in Minnesota (UMN Extension), and Oak wilt: Identification and management (Iowa State University). Hope this helps.
      -eli

  38. We had oak wilt awhile back and we injected our trees, and a year later the treatment didn’t work, so down came 13 large oaks. The cost was several thousands of dollars. My husband pointed out to me -looks like its come back, so far three of our effected we have about 9more to go. Is there any tax breaks of having them injected again? What’s one to do on a fixed budget? I am so tired and very disappointed that its come back!
    Help?

    1. Hi Angie. Very sorry to hear about your trees. It sounds like the oak wilt disease must have spread beyond your control zone. You mentioned treating some trees and removing them later, but I hope that you also hired a company with a vibratory plow to sever root grafts. Underground transmission among trees through root grafts is a very common way for an established oak wilt infection to spread. You can read more about oak wilt control options at the links near the end of the Q&A content above. I hope this helps and am sorry to hear of the loss of your trees. Oak wilt can indeed be expensive and difficult to control.
      -eli

  39. Hello,

    I just had a red oak and a white oak taken down on the 31st of March that had died over the summer from oak wilt. The Red Oak was a specimen that was over 70 years old (I counted the rings) and I’m sorry to see it go. The white oak was 16″ diameter, and was only 10 feet from the red oak. I live in a mostly wooded area, and I’m worried about infecting other trees. Some of the logs that were cut up are around 300 lbs. each, and I’m going to have to split them before I move them. I want to tent the wood as well, so I can use it for heat in 2015. How long do I have to split the wood before I run the risk of infecting other trees? Can I split it at my leisure, or do I need to move on it? Thank you!

    1. Hi David. Sorry about the loss of your trees. Your question is best answered in the fourth item under the question “What are the best ways to either avoid or minimize the probability of oak wilt infection?” above. Basically, one way or another you will need to tarp those logs pretty quickly — we recommend before the start of the next high risk season, which is imminent. You could tarp them where they are or split and move them, but we recommend keeping the red oak tarped for at least a year. There is a bit more info above.
      -eli

  40. Do you know of any data on spring spore mat formation related to growing degree days? Going by the calendar we have entered the high risk period – however we have had less than 10 growing degree days. I look forward to some feedback.

    1. Hi Gina. The major factor driving our risk status season boundaries is not mat formation, but the flight activity of the sap beetles that carry the oak wilt fungus, primarily the beetle Colopterus truncatus. We are fortunate to have one of the foremost experts on oak wilt distribution, Jennifer Juzwik of the US Forest Service, stationed in St Paul. Dr. Juzwik has authored a number of studies of oak wilt distribution by nitidulid beetles, and our risk seasons are based on her analysis.
      -eli

  41. I have a theory based on experience on my property. Oak wilt will not necessarily spread to trees next to it if you wait two years after death to cut it down. Anyone else have any experience with this?

    1. Hi Vidar. That theory is contradicted by overwhelming evidence that oak wilt will indeed spread if left untreated. Oak wilt is less virulent on members of the white oak group (bur, swamp white, white, and other oak species), and if those are present on your property that may explain your observations.
      -eli

  42. Connexus Energy is trimming trees in Blaine, MN, including oaks. I inquired and they indicated they go by your Oak Wilt Risk Status, which indicates High risk will begin Monday, April 21, 2014. It seems unwise to me for them to be wounding many oaks through pruning just days away from the High Risk period. Are they justified in this pruning of oaks right now?
    -Tom

    1. Hi Tom. Good question. We do plan our risk periods with situations like this in mind, and what the utility company is doing is not inconsistent with our risk management recommendations. While there is some risk associated with pushing any ecological threshold to its limit, that risk has to be balanced by practical considerations. I would not be overly concerned in this case, although I can understand your concern.
      -eli

  43. I am wondering about removal of live red and white oaks that are not affected by the oak wilt during this period? Is it possible to do or to wait until the high risk is over?

  44. I had storm damage on about 50 oaks on our property last June. Most we’re broken off and were impossible to seal. We have oak wilt on the property and some trenching has been done. I’ve gotten about a quarter of the hangers on the ground. Can I cut the stuff on the ground during the high risk period? Do I need to take down infected trees as soon as they are identified? Am I likely to loose all the wounded trees?
    John

  45. I have five small oaks (white I think) that I planted as sticks about 13-15 years ago. A couple are about 8 feet tall and a couple are closer to 20 feet tall. They are only 2-4 inches in diameter at the bases. Three years ago we notice early turning of leaves at the very top on one or two. Second year a little worse and I realized it was Oak Wilt. I cleaned up fall leaves pretty well and the third year it was still present but did not affect nearly as large a portion of the trees. (it was at worst 1/3rd affected in year 2 and less than that in year 3). I would like to be more aggressive this year if you think that there is anything I can do to save small trees like this that won’t cost an arm and a leg. Your suggestions would be greatly appreciated. Thanks, Ron

    1. Hi Sue-The oak wilt fungus is attracted to the scent of freshly cut oak. It’s uncertain how fresh wood can be after 2 years, so it’s safe to wait until the late summer/early fall for grinding oak stumps.
      -Matt