Post Oak , Iron Oak,
Fagaceae (white oak group)
-- Research by John J. Stransky
Post oak (Quercus stellata), sometimes called Iron Oak, or the Cross Oak, is a medium-sized tree abundant throughout the Southeastern and South Central United States where it forms pure stands in the prairie transition area. This slow-growing oak typically occupies rocky or sandy ridges and dry woodlands with a variety of soils and is considered drought resistant. The wood is very durable in contact with soil and used widely for fenceposts, hence, the name. Due to varying leaf shapes and acorn sizes, several varieties of post oak have been recognized-sand post oak (Q. stellata var. margaretta (Ashe) Sarg.), and Delta post oak (Quercus stellata var. paludosa Sarg.) are included here.
Post Oaks occur in all areas of Texas except the High Plains and Trans-Pecos. A shrub or tree ranging from 20 to 75 feet tall with stout limbs and a dense rounded canopy, it grows in dry, gravelly, sandy soils and rocky ridges. It often grows along with Blackjack Oak, and like it has been considered an indicator tree of poor soils when seen in native conditions. It is extremely sensitive to root disturbance and lack of oxygen in the root zone, so construction activities that compact the soil, pave over the roots, or change the soil grade can kill existing trees, as can overwatering, such as when a lawn has been planted around an existing tree. Post Oak leaves have a distinctive cross shape and are usually 4 to 5 inches long and they are thick and somewhat leathery. They are dark green and shiny on the upper surface and lighter green and rough hairy beneath. The bark of the Post Oak is thick with platelike scales, and is similar to that of the White Oak, but somewhat darker and often fissured into scaly ridges
The wood of post oak, commercially called white oak, is classified as moderately to very resistant to decay. The wood is hard and strong, and is very durable when in contact with soil. Its use is mainly for posts, railroad ties, mine props, and sometimes as fuel. In fact, the Post Oak sometimes is called the Box White Oak. Acorns are 1/2 to 2/3 inches long and ovoid in shape. The acorns mature in one growing season and drop soon after ripening, from September through November. In common with many other oaks, post oak begins to bear acorns when it is about 25 years old. Good acorn crops are produced at 2- to 3-year intervals.
The post oak is anti-social or intolerant of competition and is classed as intolerant of shade. Because of its slow height growth it often is overtopped by other trees, including most other oaks. On poor sites, however, post oak tends to persist and become dominant because it is more drought resistant than many of its associates. The Post Oak sets their roots much deeper that most other oaks in the sandy soils for protection from drought. The roots of most oaks are within the top 12" of the soil surface. In years of heavy rains of 40-50 inches, and then followed by a year of so or extreme drought, these deep sandy soils that normally protect them from drought, may hold excessive amounts of moisture, depleting the soil oxygen and causing root rot. This can be devastating to groves with poor drainage and mortality may show up two to three years following years of heavy excessive rains.
Post oak is susceptible to most insects, diseases, and pollutants that present a threat to other oaks. Regeneration efforts are hampered by acorns being destroyed by weevils. Insect defoliators, leafrollers, tent caterpillars, Gypsy moth, sawfly, leaf miners, and skeletonizers may cause growth losses, and when repeated, may cause mortality. The foliage also is susceptible to attacks by aphids, lace bugs, various scales, gall wasps, and mites. The trunk, twigs, and roots may be damaged by carpenterworms, borers, beetles, twig pruners, white grubs, and cicadas (locusts). Some of these cause defects that render the wood unfit for many commercial purposes.
Oak wilt, a vascular disease caused by the fungus Ceratocystis fagacearum, is potentially the most destructive disease of both the red and white oaks. It is widely distributed throughout the Central States. White oak is less susceptible to oak wilt than the red oak species, as in the white oak each cell is compartmentalizes from to the adjacant cell, thus waterproofing each individual cell. Oak wilt infection is more localized, and the tree may lose only a limb at a time, or may sustain infection by the pathogen without ever showing symptoms or take years for the tree to secum to oak wilt death. In the live oaks and red oak species there is osmosis (water movement) between each cell and the disease moves very quickly throughout the entire tree.
Chestnut blight fungus (Cryphonectria parasitica) causes many defects as well as mortality to post oak throughout its range. The tree also is subject to oak wilt (Ceratocystis fagacearum), a vascular disease prevalent mostly north of the 35th parallel, but not to the same degree as on red oaks. Soil-inhabiting fungi may cause heavy seedling mortality by damping off. Powdery mildews stunt and deform nursery seedlings.
Most oak trees are bad parents and they do not want to compete with their offspring. If willife does not consume or carry off the acorns, the tree will predispose a fungus, that will destroy germination of the acorn. Oaks trees depend of wildlife to carry the acorns away from the parent tree, as this helps create forest diversity. Weevils, also play an important part to help destroy the acorns. Post oak is a valuable contributor to wildlife food and cover. Acorns provide high energy food during fall and winter and are considered important in the diet of wild turkey, white-tailed deer, squirrels, and many other rodents. When acorns are available animals fatten quickly, go through the winter in good condition, and are most likely to produce healthy young. Leaves are used for nest building by birds, squirrels, and raccoons. Cavities provide nests and dens for various birds and mammals.
THE ROLE OF PHYTOPHTHORAS IN TREE YELLOWING AND DEATH IN TEXAS
The major symptom of Phytophthora spp. infection was a generalized slight yellowing of leaves, persisting for months or years. Later the color change accelerated, the leaves become orange, and then turned brown and remained attached. Two to four weeks later the tree died. Since 1934, symptoms of foliage discoloration ("yellowing"), retarded growth, and premature death of post oak, live oak, winged elm, and hackberry have been reported in central Texas. These symptoms are distinctly different from those caused by the oak wilt (Ceratocystis fagacearum) and oak decline (Cephalosporium) fungi. Of the 34 trees sampled, 24 exhibited "yellowing" decline symptoms. All of the symptomatic trees yielded Phytophthora in fruit culture and 83% of these yielded Phytophthora upon culture on media. 30 percent of the symptomless trees yielded cultures of Phytophthora. P. cinnamomi was observed in many of the isolates. Symptomatic trees were prevalent in places with frequent standing water, or water flows across the roots where there was exposure to slightly saline or alkali well water. Gas leaks and cattle trampling also increased susceptibility. Soil injections in the root zone with ethazol and metalaxyl provided symptom remission (greener leaves). French drains to carry saline water past low sites also resulted in symptom remission. Phytophthora played an important role in tree "yellowing" and subsequent death in Texas. These symptoms could be minimized with control.
Research is continuing to investigate the significance to the control of P. cinnamomi using phosphite. Potassium Phosphite is increasingly being used as a means of control for dieback caused by Phytophthora cinnamomi. It is a selective, systemic fungicide/nutrient energizer with a high level of environmental safety and very low non-target toxicity. This injection immediately enters the tree and begins restoring the trees ability to function again and serves to stabilize the tree. One injection protected trees for at least 4 years.
Phosphorous is an essential element for trees and critical for root production. Not only does phosphite help roots, but is actually beneficial to the regeneration of mycorrhizae on the roots of oaks and other trees. The Phosphite is highly mobile in trees and moves bi-directional in the pholem and upward to the leaves in the vascular systems. Because Phosphite has one less oxygen molecule than phosphate, a higher degree of solubility and mobility, within the plant is achieved. This unique characteristic permits phosphites to be rapidly absorbed or taken up across the membranes of plant foliage and/or roots, in both their nutritive and plant protective roles, with immediate activity on contact.
The US Constitution's haul is 26 inches thick, it is a laminated sandwich of 7" of Post Oak, 12" of Live Oak, and 7" of Post Oak. The Post Oak is the water proof factor on the outer and inner sides of the haul and with this combination the two woods provides a super strong haul. Cannon balls bounced off the haul... thus the name : "Old Ironside"