"I think that I shall never see, a poem lovely as a tree." American poet Joyce Kilmer was right on the money way back in 1913 when he wrote his seminal work, "Trees." In autumn, the leaves of deciduous trees change from green to vibrant reds, yellows and oranges. Weekend drives to view the beautiful foliage is a must for people on the East Coast of the United States. In the winter, those leaves turn brown and brittle and eventually fall to the ground to be raked up and bagged or mulched and recycled into the earth. By spring, those trees come back to life, the green leaves appear once again and flowering trees blossom into beautiful showpieces. This is the cycle of a healthy, living tree. Besides adding so much beauty to the surrounding environment, trees also provide oxygen, shade and homes for insects, birds and animals.
A healthy tree has an amazing ability to adapt and survive and is designed to withstand the harshest of elements. Trees are living, breathing things, and like humans, they can get sick and die. Tree disease can take down even the mightiest oak or redwood, but many put up a fight much like a person would when faced with a potentially deadly sickness. A completely disease-free tree is rare because of the many microscopic organisms that live on trees -- in the bark and in the root tissue. But trees are tough and usually can co-exist with the pathogens.
But sometimes tree disease can take hold in such a way that doesn't allow for recovery. When this happens, the tree can become susceptible to other diseases, and if it can't save itself, humans can step in and lend a hand. But just like a doctor treating a patient, sometimes a tree is so far gone that it becomes a liability. A diseased tree that's near death in your front yard can fall on your house and leave you with a new set of problems. When it's too sick to save, the tree needs to be removed. In this article, we'll look at some common tree diseases, how they're diagnosed and what can be done to save a sick tree.
Common Tree Diseases
There are many different diseases that can impact trees, and most are specific to a particular species of tree. Anthracnose is a disease that goes after hardwood trees, particularly American sycamores, white oaks, dogwoods and black walnuts. Anthracnose is widespread in the eastern part of the United States, where there is a high concentration of these families of trees. Common symptoms include discolored blotches or dead areas on the leaves, also known as leaf blight. Anthracnose is caused by several types of fungi that reproduce by means of spores. Spores are microscopic particles that spread through the air, especially during windy and rainy periods. They need wet weather to germinate, so anthracnose may become severe during years with long rainy periods. If a tree gets severely infected, it may lose its leaves, which is called defoliation. A round of anthracnose won't kill a tree, but repeated defoliation can weaken the tree and make it susceptible to other diseases. Its biggest impact is the reduction of shade trees in urban environments.
Root decay, or root rot, is another common cause of disease or death in trees. Roots secure the tree to the ground. They also supply nutrients and water, and the older the tree is, the larger the root structure. Trees with root problems can get blown over in wind or even fall over without warning under the weight of its leaves. It's hard to tell if your tree has root decay. There are two indicators to help determine if your tree has root decay: if the roots are broken or there is evidence of fungus.
Another devastating tree disease is the chestnut blight fungus, which has nearly wiped out the American chestnut from eastern forests. These fungus spores are spread during wind and rain and infect fresh wounds in the bark, creating a canker. The fungus pops up during moist weather and resembles an orange curled horn. To date, no cure has been found, but research is being done to develop a disease-resistant chestnut tree.
Is Your Tree Dead or Just Sick?
A healthy tree is strong and robust, but it can go south in a number of ways. Factors like wind, rain and extreme heat and cold can affect the health of a tree. These environmental causes can't be controlled, so it's important to keep an eye out for any early symptoms of ill health. Trees need to be inspected routinely: once each season and especially after severe storms. Healthy trees have full crowns, the area of branches and leaves that extend from the main trunk. Don't let green leaves fool you, though -- trees can be sick and still have a lush, green crown. These are some key symptoms that will indicate if your tree isn't healthy.
- Dead wood: Dead wood looks dry and lifeless and breaks very easily. Because it's brittle and can't bend in the wind like a healthy branch, it's likely to break. For this reason, dead branches, also called widow makers, need to be removed immediately because they're very dangerous.
- Cracks and cankers: Cracks are deep splits through the bark, and they usually indicate that a tree is failing. Cankers are holes where the bark is missing; they increase the chance of a stem breaking near the canker.
- Weak branch unions: Weak branch unions are areas where branches aren't securely attached to the tree. This happens when two branches grow closely together and bark grows between them. The bark isn't as strong as wood, and it weakens the union of the branches.
- Decay: Trees usually decay from the inside out, so it can be tough to notice initially. Fungi, like mushrooms, are good indicators, as is soft or crumbly wood.
- Poor tree architecture: Poor tree architecture means an uneven growth pattern, indicated by lopsided or leans in a particular direction. This is usually caused by years of damage from storms or improper pruning.
If you think that your tree is in trouble, you should call an arborist for a consultation. Arborists are tree experts that will be able to diagnose a disease and offer you a course of action. Not all diseased trees need to be removed, but if the tree is dead, it's best to get it out of there. You should never try to remove a tree yourself. It's a big job that requires expert precision to avoid extensive damage to property and people.
Saving a Diseased Tree
As with any disease, avoiding it is preferable to treating it and a healthy tree is inherently more disease-resistant. In order to keep your trees healthy, try the following steps:
- Avoid putting weed fertilizer on grass anywhere near the tree's roots.
- If you mulch around the tree, leave a little space around the trunk to let it breathe and avoid rotting the wood.
- If your tree has exposed roots, hand trimming that area is preferable to using a lawn mower or anything with a sharp blade.
- Watering trees during droughts is important because tree roots move up toward the top of the ground in search of water, which can weaken the tree's root structure.
- Proper pruning practices are vital, because a wrong cut can leave the tree susceptible to disease. Different species have different requirements for how to prune, so consult your local nursery or tree specialist for instructions on keeping your tree trimmed and healthy.
If you don't do what you can, it could lead to disastrous results. Some diseases have had such an impact that they've caused the loss of an entire species of trees. Dutch Elm Disease (DED) devastated the American Elm population. DED is a fungus that clogs vascular tissues, which are how trees get water. Elm bark beetles also play a part because they're attracted to diseased trees to complete the breeding stage of their life cycle. When the larvae emerge as adults, they eat the spores of the DED fungus and transmit it to other trees when they move on. Once a tree in a row is infected, it rapidly moves through the connected root systems and kills all the other trees in its path. A lack of water kills the crown, and the tree wilts and dies.
For more information on saving your trees, take a look at some information on the next page.
Related HowStuffWorks Articles
More Great Links
- Berry, Frederick H. "Anthracnose Diseases of Eastern Hardwoods." U.S. Department of Agriculture, Forest Service. Forest Insect & Disease Leaflet 133. December 1985. http://www.na.fs.fed.us/spfo/pubs/fidls/anthracnose_east/fidl-ae.htm
- "Chestnut Blight caused by Endothia parasitica." Insects and Diseases of Trees in the South. 1989. USDA Forest Service - Forest Health Protection. R8-PR16, pp. 98. http://fhpr8.srs.fs.fed.us/forstpst.html
- Haugen, Linda. "How To Identify and Manage Dutch Elm Disease." United States Department of Agriculture, Forest Service. USDA Forest Service NA-PR-07-98. http://www.na.fs.fed.us/spfo/pubs/howtos/ht_ded/ht_ded.htm
- Harrison, Marie. " Not every diseased tree can be saved." University of Florida. Thursday, July 17, 2003.http://leon.ifas.ufl.edu/News_Columns/2003/071703.pdf
- "How To Recognize Hazardous Defects In Trees." Minnesota Department of Natural Resources, and USDA Forest Service. 1996. USDA Forest Service NA-FR-01-96, pp.20. http://www.na.fs.fed.us/spfo/pubs/howtos/ht_haz/ht_haz.htm
- Pickett, Marcus. "Identifying Tree Disease." Servicemagic.com. http://www.servicemagic.com/article.show.Identifying-Tree-Disease.9763.html
- Schlarbaum, Scott E., Hebard, Frederick, Spaine, Pauline C., and Kamalay Joseph C. "Three American Tragedies: Chestnut Blight, Butternut Canker and Dutch Elm Disease. US Forest Service. http://www.srs.fs.usda.gov/pubs/ja/ja_schlarbaum002.htm
- "Shade tree disease control program." City of Minnetonka, Wi. http://www.eminnetonka.com/public_works/natural_resources/forestry/diseased_tree_removal.cfm
- Whittle, Amy. "How to Identify and Address Problems with Tree Pests: The Cottonwood Borer." Associatedcontent.com. February 28, 2007. http://www.associatedcontent.com/article/157405/how_to_identify_and_address_problems.html?cat=32
- "Why Hire An Arborist." International Society of Arboriculture. July 2005. http://www.treesaregood.com/treecare/hire_arborist.aspx