Thursday, September 10th, 2015
Trees are an important part of the landscape. Trees are planted around our homes and buildings to beautify, shade, provide oxygen, fruits, and nuts. We appreciate trees that grow “wild” in rural areas, in parks, and on other public lands. On government administered lands, rangers are responsible for seeing to the health of the trees within the set boundaries. But on private property, it is up to the landowner to take care of the trees growing there. It is important, to be able to recognize the signs and symptoms of tree diseases. Here is a list of some of the common tree diseases that we find in the Austin area.
Fire Blight is a bacterial disease that affects several types of trees including pear, apple, quince, loquat, and photinia. Signs of fire blight are the rapid blackening and desiccation of foliage and blooms; shoot tips bend in a “shepherd’s hook;” branch cankers and black, sunken twigs will come later. The cankers can retain the bacterium through the winter, then in the spring it oozes from the cankers and spreads to healthy foliage by means of wind, rain, and insects.
You can try to get rid of fire blight by pruning twigs four inches below the visible cankers. Mix one part bleach with nine parts water to make a cleaning solution for your pruners. Clean your pruning equipment with the solution between each cut and when the job is completed. Avoid excessive pruning as vigorous growth of twigs or branches makes the tree more susceptible to fire blight.
Oak Wilt is a fungus that plugs up the water-conducting vessels and reduces the water flow up the trunk of the tree. This causes the leaves to wilt and fall prematurely. Oak Wilt attacks blackjack oak, live oak, Schumard oak, Spanish oak, and Texas red oak.
Signs and symptoms to look for include one area of the tree is dying; areas around the veins in the leaves are often brightly colored; the tree appears weakened. Red oaks will die with autumn color in early summer. Live oaks die rapidly.
Oak Wilt disease is caused by beetles feeding on wounds in the tree. It can travel through interconnected roots, causing the disease to spread from tree to tree. It travels 75 feet each year in every direction, attacking any oak tree within that range.
To try to avoid Oak Wilt, prune your oak trees only in the hottest days of summer and the coldest days of winter. Seal cuts or wounds immediately with a pruning paint, then sterilize your tools. Dig a trench four feet deep and at least 100 feet from the infected or susceptible trees to sever root connections. This will keep Oak Wilt from spreading.
Cotton Rot is a fungal plant disease that attacks plant roots. It is common in areas with high summer temperatures, or in soil with a 7.2 pH or higher. Cotton Rot will attack more than 2,000 plant species including fruit trees, nut trees, ornamental trees, and shade trees, as well as cotton and most landscaping plants.
Signs of Cotton Rot are that the trees or plants wilt, die back, and lose vigor. By the time these signs are visible, however, the damage is usually severe. This makes the disease difficult to control. It moves from plant to plant, tree to tree, through the soil via the root systems. Symptoms usually become noticeable in July and August.
There is no treatment available once your tree is infected. There are a few things you can do to try to prevent Cotton Rot. Mulch your plants to keep the soil cool. If you have clay soil, add organic material. Use disease-resistant trees and plants. If possible acidify the soil around the tree roots.
Root Rot is very similar to Cotton Rot, but can be caused by a different fungus. To try to avoid Root Rot, provide for proper drainage and don’t overwater. Don’t overcrowd plants.
Phytophthora Root Rot is another fungal disease that is common in Texas. It tends to zero in most often on citrus trees that have been planted too deep. Symptoms to watch for include cracked bark, brown or brick-red bark at the soil line, or discoloration on the lower portion of the trunk. Yellow foliage is another sign of Phytophthora Root Rot. Unlike some of the other fungal diseases, Phytophthora Root Rot can be treated with a fungicide.
This is another disease that affects many species of oak trees, but is most prevalent on red oaks. Most severe in late summer and early fall, the fungus that causes the disease survives through the winter in affected foliage and twigs. The spores of this fungus are spread around by wind and rain during the following growing season. Tubakia Leaf Spot is more prevalent during wet years than during dry ones. It is also more common in oaks that are experiencing nutritional deficiencies, especially iron deficiency. This disease attacks newly transplanted trees more readily than well-established trees.
Signs to look for are dark or reddish brown circular spots on the leaves. These spots will be ¼ to ½ inch in diameter. Some spots may join together to form irregular blotches. They are generally surrounded by a yellowish halo. Severely infected leaves may fall prematurely.
Hypoxylon Canker is another fungal disease that kills stressed or damaged oaks and other hardwood trees. It is most active in times of drought. Some signs to look for are bark peeling off the trunk, the canopy dying, or dark-colored spores wherever the bark is missing.
There is no cure for Hypoxylon Canker, but it can be prevented by ensuring that your trees get plenty of water, especially during long, dry spells. If you need the help of a professional to determine your tree’s needs, give us a call. One of our certified arborists will be glad to help.