Sooty Mold

Need to know: 

  • Causes needles, branches, or leaves of trees or shrubs to appear black. 
  • Doesn’t infect plants, but grows on the sugary honeydew excreted by aphids, scales, mealybugs, and other insects. 
  • Control by preventing or reducing insect populations.  
  • Commonly infects pine, maple, and elm trees.  

Overview of sooty mold

Sooty mold fungi cause needles, branches, or leaves of trees or shrubs to appear black. The common name "sooty mold" is descriptive of the black coating or crust that is formed on these plant surfaces.

Symptoms of sooty mold

Plants may start to suffer from lack of photosynthesis caused by the obstruction of the fungal growth.

Signs of sooty mold

Black hairy or thread-like growth can be seen on any plant surface where honeydew is present.

Disease cycle of sooty mold 

Several different species of fungi often exist together to cause the sooty appearance. These fungi don't infect plants, but grow on the sugary honeydew excreted by aphids, scales, mealybugs, and other insects.

The growth of these fungi is primarily an aesthetic problem, although they can be detrimental to plant health by blocking sunlight and interfering with photosynthesis.

Image of sooty mold on pine needles
Soot mold on pine needles 

Type of Sample Needed for Diagnosis and Confirmation

The Iowa State University Plant & Insect Diagnostic Clinic can help you to investigate and confirm if you plant has this disease. Please see our website for current forms, fees, and instructions on collecting and packing samples. Contact information for each states diagnostic laboratory for U.S. residents.  If your sample is from outside of Iowa please do not submit it to the Plant & Insect Diagnostic Clinic without contacting us

Management of sooty mold

Control of sooty mold is targeted at preventing or reducing insect populations. Scales and aphids are usually the culprits in sooty mold infestations. It's important to identify the species of insect present to determine what control measures to apply and when.

In Iowa, sooty mold is most commonly spotted on pine, maple, and elm trees, but can occur in variety of plant species.

Last reviewed:
April 2022

Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Yard and Garden, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on September 1, 2016. The information contained within may not be the most current and accurate depending on when it is accessed.