Certain blobs on mulch and plants are harmless

What is that brown blob in the mulch around my plants? Is it dog vomit? Looking around, I also see light green blobs on the branches and trunk of my tree and black soot-like material on the leaves of my plant. These all seem strange. What is happening?

The blob is a slime mold. Slime molds are amoeba-like organisms that feed on bacteria and yeasts in the soil. The molds quickly appear as 4- to 6-inch patches of white, yellow, cream, gray or purple with a crusty surface. Some become a foot or more in size.

During cloudy, humid weather these molds grow out of the soil and creep onto whatever is available. Plants and mulch are used as support structures from which spores are spread by the wind, water, mowers, other equipment or movement by people or animals. Turfgrass, weeds, strawberries, bedding plants and ground covers, as well as mulches, sidewalks and driveways, may become covered with masses of gray, yellowish or black dusty spores.

While slime molds frequently cause considerable concerns, these fungi do not feed on plant tissue and are harmless. Slime molds merely use low-lying vegetation and other objects as support during their reproductive stage. When the fungal growth is heavy, the shaded plant parts turn yellow. Controls are generally not necessary since slime molds do little harm and usually disappear with the onset of dry weather. When slime mold infestations are heavy, spore masses may be broken up with a rake or a broom. Hosing with a strong stream of water is also effective but should only be done after the onset of dry weather when the threat of further development is past.

Washing off slime molds during prolonged wet weather will only help to spread the organism to previously unaffected areas. Slime molds which form thick layers or masses can be removed by hand or by removing the affected plant part.

The light green blobs on tree branches and trunks are called lichens. Most commonly, lichens appear as a perennial green or gray coating, sometimes looking dry and crusty, on the trunks and branches of trees and shrubs. There are two organisms in one, which live together in complete harmony, composed of a fungal body harboring green or blue-green algae. In the symbiotic relationship, the algae, through photosynthesis, supplies carbohydrate food to the fungus and in turn, receives protection, trapped water and mineral elements from the fungus.

In this relationship, the algae and the fungus are only distinguishable through a microscope, and the lichen persists longer than the algae or the fungus would separately.

Lichen color may include forms that are green, blue-green, yellow-green, brown, gray or even red. They take on various forms on trees and shrubs. Some are closely appressed to the bark surface and are described as crustose. Lichens which are foliose have leaf-like lobes that extend out from the bark surface. Others have hair-like or strap-like forms and are referred to as fruticose lichens.

Lichens do not parasitize trees, but use the bark as a place on which to grow. In fact, lichens grow on rocks, weathered lumber or dead branches that have fallen from a tree. Some may consider lichens unsightly, but they are not generally injurious except that when extensive, they may interfere with the gaseous exchange of the parts they cover. Because of their extreme sensitivity to sulfur dioxide air pollution, lichens seldom appear on trees in industrial cities.

Lichens rarely develop on rapidly growing trees because new bark is constantly being formed before the lichens have an opportunity to grow over much of the surface. Therefore, lichens on certain species may indicate poor tree growth. In some plantings, the more vigorous trees have fewer lichens than those of the same age nearby in a state of decline. However, few studies have been conducted to verify any correlation between lichen growth and tree vigor. Lichens proliferate when more light is provided, which could explain why they are more frequently seen on dead, leafless branches. In addition, increases in lichens are sometimes associated with moist climate.

The black soot-like material on leaves may be sooty molds. These fungi grow on "honeydew," which are sugary excretions from certain insects with piercing sucking mouth parts such as aphids, white flies and scales, as they extract food from plants such as trees, shrubs, annuals, perennials and vegetable plants. The honeydew may drip on surfaces below the plant, such as vehicles, patio furniture and ground covers. The sooty molds, dark-colored fungi, receive their nutrition from the honeydew and not the plant directly. Trying to manage the insect would reduce the sooty molds, but this can be difficult when dealing with trees.

The black sooty mold will generally "weather off" with time. Even though unsightly, it rarely hurts the plant.

Remember that slime mold, lichens and sooty mold are not harmful. For more information, contact the Daviess County Cooperative Extension Service at 270-685-8480 or email [email protected]. The publication on "Mulch Mushrooms, Slime Molds, and Other Saprophytes" can be found at https://plantpathology.ca.uky.edu/files/ppfs-gen-06.pdf. "Lichens in Landscape Plantings" is found at https://plantpathology.ca.uky.edu/files/ppfs-gen-06.pdf.

When considering what shrub or tree to purchase for your landscape, make sure it will grow in Plant Hardiness Zone 6. The United State Department of Agriculture Plant Hardiness Zone Map is based on the average minimum winter temperature, divided into 10-degree F zones. Zone 6 has an average annual minimum temperature of -10 to 0 degrees F.

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