Fungus Among Us

Fungus Among Us

Part of Ep. 1503 Focus on Foliage

UW-Extension Plant Pathologist Brian Hudelson shares some of his favorite fungal diseases and tells viewers what to do about them.

Premiere date: Jul 25, 2007

TRANSCRIPT+
Wisc Gardener Transcript: 

Shelley:
I'm at the UW-Madison Arboretum to look at the downside of gardening.  And that's some of the many fungal diseases that can affect all of our gardens and our plants.  I'm with UW-Extension plant pathologist Brian Hudelson.  Brian, I can't help noticing this really sick looking tree. 

Brian:
I think it looks great, but I'm a plant pathologist. 

Shelley:
You really get into this. 

Brian:
I really get into this sort of thing.  This is a disease called cedar apple rust or cedar hawthorn rest.  They're several related diseases that cause very similar symptoms on hawthorns and crab apples.  And what we typically look at are these interesting little orange spots on the leaves. 

Shelley:
The sick looking leaves. 

Brian:
Yeah and if you flip those over, there's a little bit of bumpiness to the undersurface. 

Shelley:
Oh yeah. 

Brian:
And that's where the spores of the fungus are produced.  Interestingly, the spores don't re-infect this host.  They actually go to another host, particularly junipers, like red cedar.  And so if you've ever seen those huge orange, slimy, marmalady masses. 

Shelley:
Ucky looks balls. 

Brian:
Yeah, those are actually the other phase of the disease.  We usually see those in mid-May to mid-June.  And the spores that are produced there are what infect these particular trees. 

Shelley:
So you have to have both the junipers and the hawthorns or the crabs to have this disease going back and forth. 

Brian:
That's right, for the fungus to complete its entire life cycle. 

Shelley:
So, this looks terrible.  What should I do? 

Brian:
Oftentimes, this disease is cosmetic.  If it's a little bit wet, we can see really severe symptoms like this, and sometimes defoliation.  But what we normally recommend as a general practice, it's not so important with this disease, but for other leaf diseases, it's always important to clean up leaf debris in the fall. 

Shelley:
So when the leaves fall, get them out of here. 

Brian:
Rake them up and either compost them if you're doing proper composting.  You can burn them if that's an option.  Bury them or just take them to your local recycling. 
Shelley:
Get them away. 

Brian:
Get them away from your yard. 

Shelley:
So you don't re-infect. 

Brian:
Right, and then the other sorts of things that we recommend for this disease is you need to become either a connoisseur of hawthorns, crab apples or junipers, but not both.  You want to break the life cycle by removing one of the hosts of the fungus. 

Shelley:
What if I want to keep both? 

Brian:
There are some options.  I would recommend using something like Chinese juniper, which tends to be less susceptible to these sorts of diseases. 

Shelley:
Brian, I know you're affectionately called “Dr. Death.” 

Brian:
That’s me. 

Shelley:
So what other tidbits of joy did you bring us today? 

Brian:
The next one that I have is one of my favorites.  This is I affectionately call "poop on a stick."

Shelley:
Now you tell me! 

Brian:
It's a disease called black knot, that's its official name. 

Shelley:
Black knot. 

Brian:
It affects cherries, plums, anything in the genus Prunus.  It's a gall disease where the fungus infects and causes this kind of cancerous mass. 
Shelley:
Cosmetic or terminal? 

Brian:
It's typically cosmetic.  What we normally recommend is to simply prune out branches that have these galls.  Prune down about four inches below.  And be sure, before you prune another branch, to dip those tools in something like 10% bleach or 70% alcohol.  Because you can very readily move disease causing organisms around from tree to tree. 

Shelley:
That's good practice any time you’re pruning. 

Brian:
Any time you're pruning, that's quite right, because you never know what's there. 

Shelley:
It's ugly, but nothing to really panic about. 

Brian:
That's right.  The next one we have is something that can be more serious.  It is kind of a pretty disease, one of the prettier that I see.  It's a disease called golden canker.  You can kind of see where it got that name, kind of a gold color to the tissue where it's infected.  This is a disease that is specific to dogwood. 

Shelley:
That's why it looks familiar!

Brian:
Yes, indeed, and lots of folks have dogwoods with these particular symptoms.  And what happens is the fungus locally infects a branch and it girdles it.  So it cuts off the water movement up to the top of the branch, starves it for water and food.  The branch will die. 

Shelley:
Also cosmetic. 

Brian:
It can be if you catch it early enough.  And in that particular case, you just prune out the infected branch about four inches down.  And then disinfect your tools.  Clean them between cuts.  And the unfortunate part is if you get this on the main trunk, it can girdle the trunk and kill the tree. 

Shelley:
How do we prevent it? 

Brian:
Basically, site selection is I think very, very important to prevent this disease.  We tend to see it on Pagoda dogwoods that have been planted right in the middle of a yard where it's hot and sunny. 

Shelley:
So, stress. 

Brian:
Stressed trees.  And this sort of tree likes shaded areas.  It wants to have a relatively cool and moist system, so we need to make sure you're watering and mulching properly. 

Shelley:
So, the right tree in the right spot. 

Brian:
That's right. 

Shelley:
Most of these have been mostly cosmetic, unless this one gets bad.  This next one is sad. 

Brian:
This is a sad situation.  This is a tree, a branch that came in.  If you look at the outside of the branch, you'd never know that there was anything wrong.  It looks like a normal tree.  Unfortunately, the homeowners noticed a lot of branch die-back with this particular tree.  And as we looked at the cut surface, we saw a lot of discoloration with rings that you can see here.  Then we started carving off the bark.  And right underneath the bark, we saw a lot of streaking as well. 

Shelley:
These stripes.  What is that? 

Brian:
That's indicative of a fungus that's gotten into the vascular tissue, the water conducting tissue.  It’s a fungus called verticillium.  It causes the disease called verticillium wilt.  It's very similar to Dutch elm disease and oak wilt in terms of how it functions.  Unfortunately, this particular pathogen has a much wider host range.  A lot of our common street trees, like maple and ash are susceptible.  A lot of our very popular spring flowering trees, like magnolia, redbud and tulip tree are all very susceptible, as well. 

Shelley:
A great deal in my yard.  What do we do if we think we have it?  It's the die-back we'd see first. 

Brian:
That's the first thing and then for this particular disease, and diseases in general, we recommend getting a sample into my clinic so you can get a formal diagnosis.  Because you really need to know exactly what you're dealing with before you decide on some sort of control strategy. 

Shelley:
And we will give your Web site so that people can do this.  But if I have this disease, can I prune it out? 

Brian:
Unfortunately, no.  It'll make your tree look better to you, but unfortunately, the fungus is throughout the tree.  And usually we expect trees with verticillium wilt to die. 

Shelley:
So, prune it to the ground. 

Brian:
After it dies and then be sure that you replace it with a tree or shrub that's not susceptible to the disease like conifers.  If you're talking about spring flowering trees, Amelanchier or Serviceberry is a very popular one.  Ginkgos are one of my favorites as well to put in as a replacement. 

Shelley:
To summarize, practice good fall clean-up, just automatically, really, with any tree and shrub. 

Brian:
That's right. 

Shelley:
If we think we have a problem, contact you and find out what the problem is instead of trying to self treat it blindly. 

Brian:
That's right. 

Shelley:
And plant the right tree in the right spot. 

Brian:
Yes, indeed, that's always a good practice. 

Shelley:
Thanks, Brian. 

Brian:
You're welcome. 

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