Roots, Shoots, Fruits & Flowers: Destructive Mushrooms, Slime Molds, and Plant Rust


Armillaria mushrooms.
Photo: Lori Dupre.

Destructive Mushrooms

Lori observed mushrooms in her landscape and wrote, “I had a tree cut down in the backyard because it was growing in the powerlines, and I needed to get some sun in the backyard. There were no outward signs of decay nor when the tree was cut down. I had the stump ground but there was a part right along the fence that could not be ground up. I put some small holes in the visible remaining part and applied some stump killer in the spring this year. I really don’t see any decay but now I see the mushrooms in that area.

I found mushrooms in my front yard too . . . almost in a line going across the front of the house with clumps of the mushrooms here and there along the line. I’ve owned the property for a couple years and there were no trees in this area when I purchased it. There was a hard spot in the front yard that was likely the top of a stump. I researched and found pictures of my house from 2013 and there was a large pecan tree then in the middle of the front yard. The stump/hard spot is no longer visible or felt when walking in the area, but a noticeable depression formed about 10 feet away. Could this be signs of the armillaria causing root rot?

I've read that armillaria is a bad fungus that spreads aggressively, can lay in wait for a new host for years and is near impossible to kill. Is there a method to kill it off other than keeping existing plants healthy? It doesn’t seem like digging out the clusters will solve the problem.

I ask you confirm the identification and any control methods.”

Dr. Raj Singh, the “Plant Doctor” for the LSU AgCenter, confirmed Lori’s identification of the armillaria fungus in her landscape. Dr. Singh also confirmed several of Lori’s comments:

  • Armillaria is a destructive disease of many ornamental trees and shrubs. Fruit and pecan trees are also susceptible.
  • It will survive in the soil for many years.
  • There are no fungicidal treatments for armillaria.


"Dog vomit" slime mold.
Photo: Jewell Paul.

Slime Molds

Jewell saw a strange growth in her yard and emailed this message, “I searched the internet for similar images and have decided this is possibly/probably yellow slime mold. I have only seen the stuff twice in my 70 years and was raised roaming the woods near Catahoula Lake and Hemphill Creek. The first time it appeared on the pine bark mulch placedaround some of our young blueberry plants. That was maybe 6 or so weeks ago and was a patch maybe 6 inches diameter. This patch of slime on the same mulch about 5-6 feet away is much larger than the first one, probably covering a square foot of mulch. (The mulch is part of more than 20 cubic yards of pine bark mulch we had hauled to our home. (Could be where we got the start of the mold.) This very distinctive mold was not visible before dark yesterday. Yes, this is slime mold. Sometimes it is called “dog vomit” slime mold.

I wonder if the moisture of the rain we got last night may have triggered the rapid growth if this slime. (And I wish I could remember if it had rained the other time it appeared.) Yes, moisture will trigger slime molds overnight.

Have you seen any of this in our area? Yes, homeowners and gardeners regularly send images and ask about slime molds in their landscapes.

I am wondering if the mold would damage our blueberry plants or other plants in our landscape? No, slime molds only appear on dead organic materials. Sometimes, gardeners will add mulch which is a good site for slime molds to establish.

And if the mold would be dangerous for us or our dog and cat, both of which are outside animals? Texas Plant Disease Diagnostic Lab reports, “Slime molds are not known to be a danger to human or animals.”

What method if any could/should we use to get rid of the mold? Dr. Singh recommends, “Controlling slime molds is often not needed. They start disappearing with the onset of dry weather. Slime molds can be hosed or brushed off the plant tissue but avoid hosing or brushing off during wet weather.”


A rust disease.
Photo: Jackie Duncan, Master Gardener, Boyce, LA.

Plant Rust

Jackie saw an infection on her plants, “Could you tell me what I’d on the underside of my leaves and should I treat them and with what? This is on my Amazonia and Ironweed.”

AHA conferred with Dr. Singh via email, and he responded, “I am suspecting it is rust. I think the black spots are teliospsores. Removing severely affected plant parts the best way to get rid of it. Preventative sprays with Myclobutanil [like Spectracide Immunox Multi-Purpose Fungicide Spray Concentrate™] or Propiconazole [like Bonide Infuse Systemic Disease Control™] containing fungicides may help manage it. There is no guarantee for full recovery.”

If you want to contact Roots, Shoots, Fruits and Flowers, please send your questions and pictures to Keith Hawkins, Area Horticulture Agent (AHA), 318.264.2448 or Also, you can be on the “green thumbs” email list by emailing your request to the address above.

“Before you buy or use an insecticide product, first read the label, and strictly follow label recommendations. Mention of trade names or commercial products in this article is for informational purposes only and does not constitute endorsement by Louisiana State University AgCenter.”

“This work has been supported, in part, by the USDA National Institute of Food and Agriculture, Renewable Resources Extension Act Award, Accession Number 1011417.”

11/1/2021 2:50:36 PM
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