More on Trees

• Trees
• CITYGreen
• Choosing a tree
• Planting a tree
• Caring for a tree
• NeighborWoods
• Tree Guardian
• Tree Legacy Program
• Growing Out Station
• Tree ailments
• Tree Plantings
• Tree Glossary
• Treevia game
• Getting Involved
• Material(s) on Trees

Tree Ailments

Urban trees face a special host of threats: air pollution, soil compaction, lawnmower and weedeater injuries, improper or lack of pruning, heat reflection, direct root damage from street paving or construction, improperly applied herbicides, overplanting, and lack of understanding about tree growth and development. For these and other reasons, urban trees can be especially vulnerable to insect and disease damage. Here is a list of some of the more common diseases and pests that affect trees and plants in our area:

Powdery mildew is one of the most widespread and easily recognized plant diseases. Even though there are several types of powdery mildew fungi, they all produce similar symptoms on plant parts. Powdery mildews are characterized by spots or patches of white to grayish, talcum-powder-like growth. Powdery mildews are severe in warm, dry climates. Therefore, the disease is common in crowded plantings where air circulation is poor and in damp, shaded areas. Infected leaves may become distorted, turn yellow with small patches of green, and fall prematurely. This problem tends to affect dogwoods and crape myrtles.

More information: http://www.ext.colostate.edu/PUBS/GARDEN/02902.html

Septoria Leafspot fungi infect leaves by spores which are dispersed by air currents or splashing rain. The symptoms of septoria leaf spot include medium uniform, purplish spots, or lesions on the leaves. These lesions do not retain the deep, purple border, although the centers of these spots become grayish. Infection usually requires moisture, such as dew, fog, or rain. Leafspots are more likely to occur on trees growing in shade, crowded together or in low spots or frost pockets. The foliage on such trees tends to remain wet longer following rain or dew. Leafspots increase in frequency late in the summer as leaves begin to senesce. Buildup of leafspots on autumn leaves generally does not affect the health of the tree and is the beginning of the natural process of decay by which the leaf is returned to the soil.

For pictures of leaf spot, check out this website: http://www.fs.fed.us/r8/foresthealth/pubs/dogwood/r8-fr14/r8-fr14.htm

Dogwood Anthracnose is caused by a fungus, Discula destructiva. This disease has devastated wild flowering dogwood populations in large areas of North America. Dogwood anthracnose is generally first identified by light brown spots on leaves. These spots then grow into large splotches occasionally bordered by purple. From the leaves, the disease then moves to the twigs and then, finally, to the main limbs and the trunk which can develop large cankers.

For pictures of infection, go to this website: http://www.na.fs.fed.us/spfo/pubs/howtos/ht_dogwd/ht_dog.htm

Oak Wilt is recognized as one of the most destructive diseases to afflict oak species in the United States. Southern species susceptible to oak wilt include: Shumard Oak, Southern Red Oak, and Live Oak. Caused by Ceratocystis fagacearum, the fungus is transported underground through the roots or overland by insect carriers such as sap beetles. With members of the Red Oak family, mortality can occur within three weeks of infection. Members of the White Oak family will die more slowly, one branch at a time over a period of several years. To identify trees infected with oak wilt, watch for wilting leaves in the upper canopy. Wilting leaves may develop yellow margins, while the interior portion of the leaf remains green. As the tree continues to wilt, leaves turn brown and fall from the tree. Since oak wilt causes drought-like symptoms, it may be easily confused with other stress-related factors. These factors include construction damage, drought stress, or insect colonization. Symptoms include vertical splits in the bark, D-shaped exit holes in the main trunk, and increased woodpecker activity. Control involves the cutting, chipping, and incineration of the infested tree(s).

For pictures of symptoms, go to this website: http://www.ohiodnr.com/forestry/Health/eab.htm

For extensive pest and disease information, please visit the USDA Forest Service at: http://www.fs.fed.us. There are a lot of downloadable guides which will give the novice and experienced gardener some good information.