Tuesday, June 14, 2011

It Looks Like a Dog Threw Up in My Mulch: Slime Molds - Harmless but Ugly!

Fuligo Septica in Mulch
Photo by Donna Steinbach (Submitted to PDIC)

Every year, we receive image samples depicting the “dog-vomit” slime mold. 

People see this ugly growth on their mulch and immediately want to get rid of it! The culprit is a slime mold known as Fuligo septica.  In spite of their names, the slime molds are not true fungi, but are related to amoebas, algae, and paramecia. These fascinating organisms spend part of their lives inconspicuously creeping through mulch, leaf litter, etc., engulfing bacteria and bits of organic matter.  Through some sort of environmental or chemical signal, they switch to the spore-producing phase of their life cycle.  In the case of Fuligo septica, the spore-producing fruiting body appears as a bright yellow froth that quickly forms a pinkish crust covering the dark powdery spores inside.  These spores will blow away and start the cycle over again.  The fruiting body can simply be raked out of the mulch or washed off with a hose. It is not toxic, although some people are allergic to the spores.  
Fuligo Septica Slime Mold
Photo by Donna Steinbach (Submitted to PDIC)

The dog vomit slime mold is not a plant pathogen. However, slime molds sometimes will grow on plant parts that touch the affected mulch, as seen on the end of a gardenia branch in the picture below.
Slime Mold on Gardenia
Photo by Mike Munster

Fuligo septica is often seen in hardwood mulches. It is less of a problem in pine bark or cedar mulches.  It is usually worse the first year mulch is applied than in subsequent years.  

While dog vomit is one of the most noticeable slime molds, many other types can be found in most back yards. 

Here are some other slime molds we have seen lately.  

Physarum Slime Mold
 On Annual Ryegrass and a weed (Carolina geranium)
Photo by Mike Munster

Physarum Slime Mold
On Cucumber
Photo by Anne Edwards

Slime molds can be startling, but up close they can be startlingly beautiful.  See the collection of images by Georgia resident Ray Simons here.

Special thanks to Mike Munster for helping with this blog idea!