OK, So I have heard about a hundred different reasons why and when you prune an oak tree. Let me set it straight, it’s actually pretty simple. When you create a wound on a tree, when pruning it, the wound will secrete sap. Bugs love sap! A bug, normally a beetle that does not have the ability to chew, will smell the sap and come to feed. At the same time Oak wilt also will form a mat under the bark, it will actually push the bark open and expose itself and it also has a sweet smell and attracts bugs to feed on it, hoping to spread its spores. This beetle may have been hanging out in a old oak, out in the woods feeding on the mat, the beetle picks up the oak wilt spores on it body (picture a bee with pollen). When it comes to feed on your tree’s wound, it spreads the spore, these spores enter the wound and now you have a problem. Depending on the species of Oak, it can kill very quickly. How do you prevent this, well its nature, so 100% prevention is pretty much impossible, and there will always be the “weird scenario” that gets through and toast’s a tree.
To prevent this, you work on oaks in the winter, it’s not because the sap drops or because the tree is dormant, the first frost is not the answer either. Its not a particular date (trees don’t read calenders to much) The best way to prevent the spread of the spore is to do it when there is very little chance of any bug feeding on the sap in the middle of winter. When the frost is in the ground, most bugs are under the frost line or they were frozen to death. How many times have we had a first frost and a couple of real cold weeks and then, all of a sudden, we have 2 weeks of 60 degree temps! The bugs will be out and about, feeding on whatever they can find. This is a typical Midwestern fall. People say after November or after first frost, these are wrong. Bugs do not work on a schedule and they do not get laid off. So yep, in the middle of winter, when there is 2 ft of snow on the ground and your nostrils burn every time you breath! That’s the best time to do it! So far, by sticking to this plan, I have never lost an oak to oak wilt. Not saying that this is the final rule, every situation is conditional. This in nature after all. This is gives your tree its best chance to avoid the bugs. No bugs, no spread. Oak wilt can get into the tree via the root system, but we will touch on that later. So, when you see someone pruning an oak in the middle of summer, they are wrong, in October, they are wrong, I stick to late December to the middle of March, based on the conditions outside of course. Sometimes it comes early. It is all based on the weather and when temps allow. There are 2 main reasons why it is done improperly 1.They don’t care about your tree, just care about making revenue 2. They do not want to work in the freezing cold. Either do I, I do it because that’s the right thing to do.
There are a few other Certified Arborist in the area that prune them whenever. They know the reasons why it should be done in the winter, yet they do it and they know that it is wrong, these are the guys who became certified for the wrong reasons, just to flash a piece of paper in a face. If they practiced true Arboriculture, They would not do this.
Roots, if you have a tree that has been identified as having Oak Wilt, you need to look and see where the next closest oak is. If you have one that is withing 50yds, you need to inspect it right away. Remember, the majority a root system is in the first 18″ of soil and can be three times the height of the tree in a 360 radius,. In other words, if you have a 100′ tree, you probably have about 300′ of roots all the way around it. Or 600′ across. Have a ISA Certified Arborist check it out. To aid in prevention, the only way to do this is to double trench around the tree. Oak wilt can travel thru the roots system of the same species and infect other trees. If you have different species, it is unlikely that they will transfer the wilt, but it has happened. Trenching can stop this by severing the connected roots of adjacent trees. The second trench is kinda for good measure, it will help in slowing down the trees making that underground connection again, killing the roots in between the two trenches. Yes, this is a big mess and very costly, but it works pretty darn good.
If you have a oak that has been damaged in a storm and you have no choice but to remove a few pieces during the warmer months, this is the one and only time I would recommend a sealer. Wound sealers are bad for trees and plants, no matter what the manufacturer says, it messes up the trees natural ability to care for itself. It will screw up the process of closing the wound and many times will result in a “pocket”. This is especially true of oaks, however, it is the lesser of two evils. The sealer will most likely not kill the tree, but it will prevent the bugs from feeding on the tree and spreading oak wilt. There is a specific product for this called TreeKote. All other products should be avoided. Since we are on the topic, NEVER put cement, foam, tar, gravel or any other foreign material in a wound or cavity, it will hurt your tree and it does not prevent anything.