Horticulture Hotline 05/23/23
By Bill Lamson-Scribner
Bill,
On the bark of my tree, I noticed grayish growth. I can peel this growth off easily. What is this growth and is it hurting my tree?
I have been asked some form of this question in Possum’s, on the radio, or in the grocery store many times. It sounds like you have lichens. Lichens are grayish-green organisms that are a cross between fungi and algae. They make their own food and collect their own water and minerals, so technically they do not harm the plant or tree on which they are growing. They are a sign that the tree or shrub is not flourishing. Lichens do not hurt what they are growing on – they are a sign that what they are growing on is hurting!
Since lichens manufacture their own food through photosynthesis, they need sunlight to carry on photosynthesis. A healthy actively growing plant or tree is the best defense against lichens. If the tree or shrub has a thick canopy, the lichens will not survive since they need sunlight to manufacture their food. Culturally, the plant must be planted in an area that provides the conditions that the plant can thrive, so it produces a dense canopy that will shade out the lichens. Proper fertilization based on soil tests and proper pruning will help to keep the canopy thick. Think of trying to grow grass under the thick canopy of a tree – the grass needs sunlight for photosynthesis like the lichens and will not grow in the dense shade.
Lichens thrive in these conditions which are not very favorable for plant growth. With our on-again, off-again rain, it is hard to control these moist conditions. If you have an irrigation system, be sure you are not over-watering, as this contributes to the problem. Irrigation systems are great; however, if over used can cause great problems in the landscape. Large patch fungus and lichens could be a couple of examples of over-watering issues.
The best control for lichens is cultural controls. Try to minimize the moisture in the soil and maximize air movement around the plants and trees. Pruning to increase air movement will help dry the soil. Excessive mulch whether fallen leaves, pine straw or wood mulch will keep moisture high in this area and should be limited to 2-3 inches in depth. A good fertility program derived from a soil test helps a whole bunch.
Lichens, although a bit unsightly, do not harm the plant. If a plant or tree is planted too deep, lacks proper fertility, stays too wet or too dry, is planted in the sun when it prefers the shade or visa versa, improper mulching, in a windy beach setting when the plant prefers a different environment … Happy plant = no lichens.
Mistletoe is a parasitic plant that lives in our trees. It manufactures its own food; however, it has a root-like growth that penetrates the bark and collects minerals and water from the host tree. If left to grow, it will eventually kill the host tree. Mistletoe produces seeds that birds eat and spread. These seeds also get under the soft bark and germinate spreading the parasitic plant. Mistletoe can get you a kiss during the holiday season, but it can also kill a tree.
Soil Tests, pots, potting soil, soil moist, neem oil, horticultural oil, Cotton Burr Compost, gift certificates, rodent control, roach control, mole crickets, fire ants, moles, pruning (azaleas and camellias), grass coming out sssllloooww are just a few things that seem very popular right now.
Always read, understand, and follow product label. The product label is a Federal Law.
