Sooty Mold

Class: Insects
Common Name: Sooty mold
Scientific Name: A collective of different sac fungi (Ascomycota)
Potential Host:

There is a wide range of ornamental and cultural crops that can develop on the surfaces where honeydew is present.

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Who Am I?

Sooty mold is a general name for a collection of different species of fungi that grow on the honeydew secretions found on plants. The existence of such sugary substances on plants is often related to the presence of sap-sucking insects and could point to a possible pest infestation. Aphids, mealybugs, whiteflies, cicadas, and scales are just a few examples, but tend to be the most well-known ones.

Those insects feed from the plant using their mouths to suck up sugary fluids. They can’t utilize all of the nutrients inside the fluid; therefore, they assimilate what they need and excrete the rest as the byproduct we call “honeydew.” Wherever there is honeydew, let it be leaves, twigs, fruits, or concrete, sooty molds can develop.

Mycelium is black and can give leaves or other plant parts the appearance of being covered with a layer of soot (hence the name.)

Sooty molds can damage the plant by coating the leaves to the point where reduction in sunlight is critical. Without enough sunlight, photosynthesis is reduced, thus leading to slower plant growth. In addition, coated leaves might prematurely age causing premature leaf drop.

Control Measures

The sooner the better: It’s easier and more cost effective to eradicate sooty mold presence while it’s still in the initial stage. Make it a routine to monitor the field regularly and search plants for the presence of sooty mold and honeydew secretions on a weekly basis. Keep in mind that any current infestation of sap sucking insects might, in the future, lead to the development of sooty mold.

Because the presence of sooty mold most likely points to an underlying pest infestation, one firstly needs to get rid of the unwanted sap sucking guests that triggered the sooty mold. 

Then it’s time to deal with the mold. The best way to do it doesn’t require expensive fungicides. You just need to wash the honeydew. Here, basic chemistry comes to our aid; a high volume, 70+ liters of water per dunam(0.25 acre), an application of a known commercially available detergent or soap product designed specifically for agricultural uses can help dissolving the sticky honeydew secretions, thus reducing surfaces suitable for sooty mold development. Repeated use of detergents (two or more consecutive applications) can achieve a significant reduction in the presence of sooty mold.  Moreover, detergents and soaps containing surfactants (compounds that reduce the surface tension of solutions) enhance the capability to wet and wash arthropods off.

Most of the commercial detergents and soaps products are labeled as organic suitable.

Caution and careful notice should be taken when using any plant protection products (insecticides, fungicides, and herbicides). It is the grower’s sole responsibility to keep track of the legal uses and permissions with respect to the laws in their country and destination markets. Always read the instructions written on labels, and in a case of contradiction, work in accordance to the product label. Keep in mind that information written on the label usually applies to local markets. Pest control products intended for organic farming are generally considered to be less effective in comparison to conventional products. When dealing with organic, biologic, and to some extent a small number of conventional chemical products, a complete eradication of a pest or disease will often require several iterations of a specific treatment or combination of treatments.