By Bill Snyder
Our Mahoning County Plant and Pest Diagnostic Clinic has received many reports of what seems to be similar organisms, namely, mosses and lichens. In fact, the two are dramatically different. Where mosses are primitive plants, lichens are a beneficial association of a fungus with an alga or a cyanobacterium.
Most homeowners bringing these organisms to the extension office find them on the bark of trees. Others find lots of moss in areas of the lawn where grass does not grow well. One recent sample was both moss and lichen growing on the bare ground in a vegetable garden. That one was most likely due to the perfect growing conditions provided by lots of moisture during this year’s growing season.
Mosses are small spore-producing plants that lack a vascular system to transport nutrients and water internally. The plants have leaves, stems and rhizoids (root-like structures that anchor, but absorb no water or nutrients). Mosses are usually found in damp, shaded environments. They tend to favor conditions where the soil is acidic, compacted, poorly drained and nutrient-poor. In general, conditions favorable to the growth of turf grass are generally incompatible with moss growth.
The first step in any moss control program is to test the soil. If the soil is too acidic or deficient in nutrients, the soil test report will indicate how much fertilizer and lime to apply. Over time, the improved soil conditions resulting from applying amendments will help the turf grasses compete with the moss. If shade and moisture are the limiting factors for good turf growth, steps should be taken to correct the situation by pruning or using more shade-tolerant grasses. Turf improvement will automatically lead to moss control.
Unlike mosses, lichens are composed of two organisms living together, each contributing to the survival of the pair. One component is a fungus, part of a large group of organisms that include molds, yeasts and mushrooms. This fungal portion forms a stable structure for the lichen and is also capable of extracting nutrients from supporting structures. Fungi are well known for their ability to break down complex molecules from their surroundings for use as metabolites.
The second component organism in lichens is an alga or cyanobacterium, which are aquatic photosynthetic organisms. They are protected by the fungal threads, which supply nutrient minerals and other essentials for the lichen. The algal portion also provides enough carbohydrate for the lichen to thrive on the surface of tree bark or even on a rock.
Control of lichens is almost never a necessary. They may cover the bark of a tree trunk but pose no damage to the tree. In fact, lichens are extremely sensitive to air pollution and their absence can be used as a measure of air pollution.