Our oak tree prune
Trimmed our oak tree, exposed a hollow branch leading to the trunk, should this be plugged up? Is this a problem for the tree??
Itasca County Minnesota
We no longer normally recommend any sealing of wounds or cuts as studies have shown that sealing seals in pathogens and the tree does a lot better job of sealing its wounds than anything we can buy.
Oak wilt is a big problem this time of year and pruning oaks is not recommended, but if any damage occurs use of a tree sealer is recommended. However, oak wilt has not been reported in our area yet (See https://extension.umn.edu/plant-diseases/oak-wilt-minnesota). This does not mean that it isn't around, it just hasn't been reported yet and the map shows it is getting very close. So, you should avoid pruning April-July when the risk is high. See https://www.dnr.state.mn.us/treecare/forest_health/oakwilt/index.html
If it is just a branch that is hollow, you can cut it off flush with the tree. See https://extension.umn.edu/planting-and-growing-guides/pruning-trees-and-shrubs. If the trunk has started to rot (is hollow), the tree may be in trouble. If the hole is into the trunk you may want to consult a certified arborist to see if the tree is in danger of coming down (https://www.treesaregood.org/findanarborist/findanarborist)
See https://www.mortonarb.org/trees-plants/tree-and-plant-advice/horticulture-care/trunk-wounds-and-decay for more info on tree cavities.
Good luck with this.