Oak Wilt ID and Treament

Oak Wilt ID and Treament

Part of Ep. 205 Autumn Highlights

Learn how breaks in the bark of an oak tree can provide the opportunity for oak wilt fungus to infect the tree.  Bruce Allison, of Allison Tree Care in Madison, suggests ways to prevent this disease.

Premiere date: Aug 31, 1994

TRANSCRIPT+
Wisc Gardener Transcript: 

Shelley:
Leaves on the ground is a common site this time of year, but if they fall early, that can be the sign of a problem. I'm with Bruce Allison, of Allison Tree Care in Madison. And, we're on Lake Wisconsin in Colombia County to talk about oak wilt. That's what's causing that, right?

Bruce:
That's right, Shelley. This fall of leaves is certainly an indication that the home owner should look up and in this case we're looking at a large red oak nearby that has large sections of dead, already wilted leaves. This is caused by the fungus, oak wilt. The oak wilt has entered the vascular system of this oak tree. It has caused those vascular cells to become closed. Therefore, no water is moving up, into the crown of the tree. The leaves wilt and fall on the ground.

Shelley:
Is it fatal?

Bruce:
This particular tree should be dead in two or three weeks. If it was a white or a burrow, they also will get oak wilt, but much less likely to die from it.

Shelley:
Well, how does this spread?

Bruce:
Very interesting. Like-species oaks, when they're nearby, will actually graft roots underground.

Shelley:
Like these here?

Bruce:
Exactly. Perfect example, these trees are very healthy over here. They have grafted roots, which is a perfect bridge for the oak wilt fungus to move from an infected tree nearby into these trees. It's very important when you have a group of healthy trees and an infected tree nearby to sever those roots and stop that bridge from infected tree to healthy tree.

Shelley:
So, we know how it spreads from an infected tree. How does it get here in the first place?

Bruce:
Well, back here, where we have an existing pocket, this was probably initiated by a wound that occurred at a vulnerable time of year and that is early spring when those leaves are just starting to open up until full leaf development. A break in the bark, at that time, if the oak wilt is present in spore form, can light on that wound and cause an infection. Another way for that to occur is for the common picnic beetle to visit an infected tree, pick up spores, and carry it over to a healthy tree-if a wound exists on that tree.

Shelley:
So, this beetle, shiny black with orange spots is the culprit.

Bruce:
It's the culprit, very common. That's why it's so important not to prune during that vulnerable time. Or, if a break in the bark does occur, to put tree wound dressing. And, I know that goes against what we normally say. Normally, if you're pruning, there's no need to put tree wound dressing on. The exception is here and it's very important to follow that rule.

Shelley:
Okay, should we stop buying-- or growing oaks?

Bruce:
Not at all, oaks are a very important species. I would just advise home owners to, when they're planting new oak trees, put them further apart. Prevent that chance for oak-- for grafts to occur. And certainly don't prune during the vulnerable time.

Shelley:
Okay, thanks, Bruce. So, go ahead and plant oaks, but remember, the safest time of year to prune is fall and winter.

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