Black Mold Is on My Yard Soil

Mold Varieties

• Lawns are susceptible to many kinds of mold strains including black smut, black spot, rust and Pythium blight. At the very least, these molds are unsightly, causing black spots on vegetation and often eventual plant death. One of the most destructive varieties, Stachybotrys chartarum--commonly known as the definitive "black mold"--can also inhabit decaying organic material found in topsoil.

Dangers

• Molds generally aren't dangerous to humans unless you ingest them. However, all molds produce spores, which are essentially seeds contained in a hard, spherical outer shell. The egg-like spore's outer shell dissolves away when it comes into contact with moisture, allowing the mold seed contained inside to take root, multiply and spread. In the case of chartarum, the warm, wet conditions inside the human lung and sinus cavity provides the perfect environment for growth. Chartarum can clog the lung's oxygen-carrying pores, and it excretes toxins that cause serious health problems.

Mold in Soil

• Some molds actually grow in the soil while others simply drop their spores onto the top of the soil. Mold spores are microscopic, making them almost impossible to distinguish by the naked eye from the soil itself. A number of varieties grow on the soil's top surface, and penetrate by only about an inch. Very few grow well in deeper soil. Black smut and black spot manifest as a dark fuzz on the blades of grass and leaves, while rust looks like red/yellow/black pustules on the leaf or blade undersides. The white mold you might see growing on the soil surface itself is probably saphrophytic (decaying organic matter) and is harmless to plants.

Causes and Prevention

• The base cause behind mold in soil is the presence of mold spores, but a number of factors provide mold with an environment conducive to growth. Most molds thrive in conditions of high moisture and low oxygen. Preventing fungus on the lawn is generally a matter of depriving it of water and increasing the airflow through the soil. If you see black mold on the soil or plants, the simplest solution is to reduce watering, and to mow and de-thatch your lawn to increase the amount of sunlight and oxygen that reaches the soil below. If your lawn or soil doesn't respond to these measures, consider a chemical or professional physical treatment.

Chemical Treatment

• Commercially-available fungicides kill most types of mold colonies, but some will kill the plants as well. Fungicides that contain copper, for example, are useful because copper is toxic to most molds, but plants tolerate it well to certain concentrations. Watering a copper-based fungicide into the soil won't stop existing mold spores from growing into mold in the future when they are exposed to water since they have already been disseminated, but it will kill existing colonies, effectively stopping them from producing additional spores.

Physical Treatment

• If chemical treatment isn't effective, the next step is to dig up the soil a few feet at a time to a depth of a few inches, spread it into a thin layer on a tarp and allow it to air-dry. Consider sprinkling the soil into a bonfire to incinerate any spores, then mix the soil-ash mixture back into the lawn. Wood ash is an excellent fertilizer rich in calcium, potassium, copper, magnesium, molybdenum and zinc, but bear in mind that it can decrease soil acidity, so adjust the pH as necessary by adding sulfur to the soil/ash mix.