Trees - Oaks

Members of the oak family represent one of the most desirable groups of trees planted in Texas. They are widely adapted to Texas soils and growing conditions. Seldom do they require pesticide treatments for either insects or disease. Depending on the species, canopy shapes vary from an umbrella to an upright growth. Select species that are suited to the area where they are to be planted. Native species are normally more successful than non adapted selections. Soil pH, drainage and soil type are some of the environmental factors that influence the growth and survival of all trees. Avoid planting trees that require modifying the soil pH or texture to get proper growth. The live oak, Spanish oak or Shumard oak are widely adapted cultivars. However, water oak, bur oak and chinkapin oaks should be considered for planting in areas where they are adapted. The bur oak and chinkapin are white oaks and are resistant to the oak wilt fungus.

Live Oak (Quercus virginiana and Q. fusiformis) are widely adapted species. In addition there are numerous hybrids between the two species. They provide shade during the winter as well as summer months. Leaf shed is during the early spring and trees will be completely defoliated for only a few weeks. When cared for properly, live oak has a moderately rapid rate of growth. The crown of a mature live oak may spread as much as 150 feet and reach a height of 40-50 ft. it is highly desirable as a landscape tree.

Studies have shown that they can be replanted successfully in old and developing oak wilt centers. Precautions must be taken to prevent wounding. Wounds attract sap feeding beetles that carry the oak wilt fungus spores. If the tree is wounded or it has to be pruned, Immediately paint with a wound dressing. The dressing forms an insect barrier.

Major foliage diseases of live oaks are: oak leaf blister, anthracnose and powdery mildew. Seldom do these diseases become severe enough to require treatment.

Spanish Oak (Quercus shumardii var. texana) is a native red oak in the Texas Hill Country. It is adapted to high pH soils in Central Texas. Its leaves turn brilliant red in the fall. The tree is small to moderate in size, rarely reaching more than 30 ft. in height and a trunk more than 10 inches in diameter when mature. In landscape plantings it is frequently planted as a multiple trunk tree. After the leaves turn red in the fall, they are retained on the tree for several weeks after the first frost. During the summer the leaves are a dark green and have a shinny appearance. When properly cared for the tree has a moderate rate of growth.

Like the live oak it is susceptible to oak wilt, but if precautions are taken, chance of infection is low. One disadvantage of the Spanish oak and also the Shumard oak is that they sometimes form fungal mats when they become infected in the fall and die during the winter. For this reason, if they become diseased, it is important to remove them before they can form mats in the spring. If left in place, insects visit the mats and spread the fungus to nearby trees. Although a concern, this should not prevent planting of these trees in the home landscape. Additional diseases are: Powdery mildew, oak leaf blister and anthracnose. Seldom do trees require spray applications to control the diseases.

Shumard Oak (Quercus Shumardii) is one of the larger Southern red oaks and is native to the East Texas. There it is found in well drained alluvial soils. When mature it forms a tall tree, reaching a height of 100 ft. and a trunk diameter of 3 ft. It is deciduous. And like Spanish oak, its leaves are brilliant red. During the growing season, the leaves are large and dark green in color.

It is also susceptible to oak wilt, but if the precautions outlined for live oak are followed, the chance of it become infected when transplanted in the landscape is only slight. Like Spanish oak, it sometimes forms fungal mats when it develops symptoms in the fall and dies during the winter. When symptoms are observed, it is best to remove the diseased tree.

Major foliage diseases: Powdery mildew, anthracnose, actinopelte (first few years) and oak leaf blister. Seldom does infection become severe enough to require treatment. Iron chlorosis is sometimes a problem when planted in alkaline soils until the roots have a chance to become established. Soil applications of iron chelates or other iron sources will provide additional iron until the tree is established.

Water Oak (Quercus nigra) is native to many areas of Texas. When mature it reaches a height of 80 ft. and the trunk is 1-3 ft. diameter. It is an upright growing deciduous tree. Although it is reported to be susceptible to oak wilt in other areas of the United States, losses have not been observed in Texas. This may be due to the fact that it has not been a major species in any of the areas where oak wilt has been observed. The same precautions as outlined for planting other susceptible oaks in an oak wilt area should be followed when water oaks are planted. It is a deciduous tree.

Major foliage diseases: Actinopelte leaf spot, oak leaf blister and anthracnose. Significant losses have been observed from stress and hypoxylon canker.

Bur Oak (Quercus macrocarpa) is member of the white oak group. It grows to a height of 60-80 ft. with and a 2-3 ft. trunk diameter. The crown is rounded. The leaves are deciduous and large. Rate of growth is relatively slow. It is well suited to planting on calcareous soils. The acorns are large and showy.

Bur oak is a white oak and resistant to the oak wilt fungus. It is an excellent landscape tree.

Foliage diseases: No foliage diseases have been consistently associated with bur oak trees in Texas. An infestation of aphids and mites will sometimes cause the terminal leaves to be misshapen.

Chinkapin Oak (Quercus muehlenbergii) : is white oak that can be grown in many of the areas where oak wilt is a problem. Like bur oak, it is a deciduous oak. The chinkapin oak has a upright growth habit. Mature trees reach a height of 50-70 ft. with a trunk diameter of 1-3 ft. Leaves are large. Acorns are moderate in size. It grows best on well drained calcareous soils. It is normally found growing in soils that have a pH of 7.0 or above.

Foliage diseases: Anthracnose is the only foliage disease that has occurred enough to be considered a problem on this species.

Due to difficulty in transplanting, blackjack and post oak are not suggested as replacement trees in oak wilt areas.