Current status: High risk.
as of 10am March 18, 2012
Current oak wilt status in Minnesota
Q: Why the early transition to the high risk period in 2012?
A: Forecasted temperatures of 65° F to 76° F accompanied by sunny or partly cloudy conditions between 13 March and 20 March will be conducive to emergence of Colopterus truncatus. This is one of the two principal nitidulid beetle species that transmits the oak wilt fungus. The lack of snow cover and these higher than average temperatures are the basis for prediction of the earliest calendar date this website has reported for shifting from “safe” to “high risk” in early spring in Minnesota. Temperatures between 43° to 85° F are conducive to oak wilt mat formation.
Add the oak wilt risk status widget to your site.
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.
High Risk months in Minnesota are April, May and June.
Low Risk months are 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.
Third, injection 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 40 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.
Q. Can I add the University of Minnesota oak wilt widget to my site?
A. Yes! You can download the embed code here.
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!
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
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
Hmmm… First we need to know for sure whether you’re an oak. Are you ring porous or diffuse porous?
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.
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!
Hi Nick. As of April 2010, the maps on the Minnesota DNR’s oak wilt page don’t show any known oak wilt near the Superior National Forest. A more detailed map on the Forest Service’s How to Identify, Prevent, and Control Oak Wilt page shows oak wilt as far north as Isanti and Kanabec counties, but no further. Based on this info, you should be safe up in the Superior NF.
-eli
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
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
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”
Hi Steve. Are the symptoms you’re seeing similar to those described in this article? http://www.ipm.iastate.edu/ipm/hortnews/node/312
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
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
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
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!
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?
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.
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,
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
Thank you. I guess it’s nature’s way of pruning.
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
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
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.
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.
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.
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.
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
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.
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
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
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.
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
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?
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
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?
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
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.
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
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.
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
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?
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?
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