Yuck, what’s that brown stuff in the mulch next to the shrub? is it dog poop I also notice light green spots on the branches and trunk of my tree. What’s happening?
Keeping the environment moist from frequent rain showers creates the perfect conditions for the development of green, crusty material on the bark of trees and light brown patches in the mulch.
It may seem like an invasion or terrible diseases. However, the crusty material on branches and trunks, called lichen, is easier to see when it’s wet. The light brown blobs that can form on plants and mulch are caused by slime mold, not a dog.
Thankfully, both are harmless.
Most commonly, lichens appear as a perennial green or gray coating on the trunks and branches of trees and shrubs. It’s actually two organisms in one, consisting of a mushroom body that houses green or blue-green algae that live together in total harmony.
In the symbiotic relationship, the algae provide carbohydrate food to the fungus through photosynthesis and in return receive protection, trapped water and mineral elements from the fungus.
In this respect the algae and fungus are distinguishable only by a microscope, and the lichen persists longer than the algae or fungus separately.
Lichen color can include forms that are green, teal, yellow-green, brown, gray, or even red. They take different forms on trees and shrubs. Some lie close to the surface of the bark and are described as crusty.
Leaf lichens have leaf-like lobes that extend from the bark surface. Others have hair-like or strap-like shapes and are known as fruit braids.
Lichens do not parasitize trees but use the bark as a place to grow. In fact, lichens grow on rocks, on weathered wood, or on dead branches that have fallen from the tree.
Some may find lichen unsightly, but they are generally not harmful, except that when they are extensive, they can interfere with the gas exchange of the parts they cover. Due to their extreme sensitivity to sulfur dioxide air pollution, lichens are rarely found on trees in industrial cities.
Lichens rarely develop on fast-growing trees because new bark is constantly being formed before the lichens have a chance to grow over much of the surface.
Therefore, lichens can indicate poor tree growth in certain species. In some plantations, the more vigorous trees have fewer lichens than their nearby peers in a state of decline.
However, few studies have been conducted to verify a link between lichen growth and tree vigor. Lichens thrive when more light is available, which may explain why they’re more commonly seen on dead, leafless branches. In addition, lichen increases are sometimes associated with a humid climate.
Slime molds are amoeba-like organisms that feed on bacteria and yeast in the soil. It looks like a dog has an upset stomach. The molds quickly appear as 4- to 6-inch white, off-white, gray, or purple patches with a crusty surface. Some grow a foot or more.
During cloudy, humid weather, these molds will grow out of the ground and creep onto whatever is available. They use the plants and mulch as support structures from which spores are spread by wind, water, mowers, other implements, or human or animal movement.
Lawns, weeds, strawberries, bedding plants and ground covers, as well as mulch, sidewalks, and driveways can become covered in masses of gray, yellowish, or black dusty spores.
While slime molds are often a major concern for homeowners, these fungi don’t feed on plant tissue. Slime molds use only low-lying vegetation and other objects for support during their reproductive phase.
In the case of severe fungal infestation, the shaded parts of the plant turn yellow. Controls are generally not needed as slime molds do little harm and usually go away as the drought sets in.
In the case of heavy slime mold infestation, spore masses can be broken up with a rake or broom. Hose down with a strong water jet is also effective but should only be done after the onset of drought when the risk of further development has passed.
Washing off slime mold during prolonged wet weather only helps spread the organism to previously unaffected areas. Slime molds that form thick layers or masses can be removed by hand or by removing the affected part of the plant.
Remember that lichen and slime mold are not harmful. For more information, contact the Daviess County Cooperative Extension Service at 270-685-8480 or email firstname.lastname@example.org.
When considering which shrub or tree to buy for your landscape, make sure it grows in plant hardiness zone 6. The US Department of Agriculture’s plant hardiness zone map is based on average minimum winter temperatures, broken down into 10-degree zones. Zone 6 has an average annual minimum temperature of -10 to 0 degrees. Plants growing in zone 7 with an average minimum temperature of 0 to 10 degrees would not survive the winter in our zone 6. They will be pretty in summer but will die in winter unless the plant is grown in a sheltered area where it stays warmer. Zone 4 and 5 plants will grow here, but some of them may suffer from the heat, but they will survive our cold temperatures.