There is a wide range of ornamental and cultural crops that can develop on the surfaces where honeydew is present.
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.
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.
*Names marked in red are considered to be highly poisonous to beneficial insects.
*Names marked in green are considered to be organic and IPM (integrated pest management) compatible.