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Red Oak Borer

Enaphalodes rufulus (Haldeman)
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Adult Red Oak Borer


Oak decline, an insect/ disease complex, is a natural occurrence with a variety of causes. Trees are subject, or predisposed, to oak decline ( See article by factors including relatively old age (90+ years); shallow, rocky soils; ridge top and upper slope locations; and combined effects of several years of severe drought. In addition, decline may be triggered by factors including repeated early spring attacks from insects ( red oak borers, two-lined chestnut borers ) and diseases armillaria root rot  and hypoxylon cankers. (See ).


Of these factors, the red oak borer has become dominant over the past few years. Forest managers became aware of the growing red oak borer problem.They have worked with scientists from the USDA Forest Service, Forest Health Protection, to initiate studies, conduct reconnaissance flights and establish research plots in affected areas.

Although most of the focus has been on the conditions of oaks in the national forests, private forest landowners and homeowners face the same problem. The past several years of extremely dry summer conditions and then flood conditions have weakened trees throughout the state. This has created conditions ideal for development of red oak borer infestations in these trees.

The red oak borer is a native insect in eastern US and to Texas, and it is a normal occurrence for large old red oaks to be attacked by this insect. The red oak or Texas Spanish oak is the most prominent victim however the Texas Live Oak has also fallen victim to red oak borer. However, trees are not normally killed. The main damage from this insect is degradation of lumber caused by the large galleries and stains. However, in the past few years the red oak borer populations have built up tremendous numbers. A few red oak borer larvae won’t kill most trees, but the high populations that are currently present in our forests are definitely causing extensive tree mortality.


The red oak borer adult beetles are robust longhorned beetles and about 1 1/4 inches in length. Their antennae are very long, almost doubling  body length.  The antennae are about as long as the body in females and twice as long in males, or about 2 1/2 inches in length. The newly emerged adult is light brown in color. Their rust brown color blends well with the bark surface, and they are rarely seen. The pale, robust larvae have very small legs on  he thorax.  Mature larvae are large, about 1 1/2 inches in length, robust and shiny white except for stout, dark mandibles and amber spiracles. The larvae have tiny four-jointed legs.


A generation of red oak borers is completed in two years. In the central U.S.,  most adult beetles emerge in odd numbered years – 1999, 2001, 2003, etc. In the extreme southern U.S., red oak borers occur every year, but the majority still emerge in the odd numbered years. During the past summer (2001), red oak borer adults emerged from previously infested trees in June and July. They emerge almost entirely at night, and most activity occurs at night. Adults generally do not feed on twigs and foliage as do other insects in this group of borers, but feed on water and sap ooze. Females mate once or more and deposit an average of 200 eggs in bark crevices, under bark scales, under lichen patches and under tightly attached vines. Eggs hatch in 10 to 13 days and bore directly into the phloem of the tree. The entry holes are tiny pinholes and are difficult to detect the first fall and winter after eggs hatch. Dark stain spots around the damaged area on the tree the following spring and summer make entry areas more prominent and easier to detect. (See article Slime Flux

By the end of the first growing season, larvae make small oblong holes in the bark for frass ejection and are well established in cave-like burrows in the inner bark or phloem. During spring and summer, larvae burrow upward and laterally in the phloem, then upward. In early summer, larvae begin etching the wood, and by midsummer begin to enter the sapwood. Larvae excavate 1 1/2- by 2 1/2-inch chambers in the phloem-cambium area of the tree. From this chamber, an oval gallery or tunnel is extended at an angle upward into the wood of the trunk for about 2 inches, then straight up for an additional 2 to 4 inches. Each emerging adult chews an oval 1/2-inch exit hole in the tree. Wounds caused by larval feeding usually heal after one to two years leaving vertically elongated bark scars with median seams.

Management and Control

Natural controls are important in reducing the red oak borers’ overall population. Larval mortality in the first few days of life averages 40 percent by birds and other predators. In addition, fermenting sap, nitidulid sap beetles and ants cause mortality of up to 30 percent in older larvae. Lepidopterous woodborers (“carpenter worms”) also invade wound sites in the later stages of larval development and kill 4 to 5 percent of the larvae. Overall survival of the red oak borer larvae is estimated to be between 6 to 16 percent of the eggs that hatch.

Red oak and live oak trees in urban areas need special attention to survive all the difficult conditions to which they are subjected. Maintaining tree health is the best preventative measure to guard against insect and disease infestation. Deep-water irrigation in times of drought stress is essential to maintain tree vigor. Late winter or early spring fertilization is another good management practice. Urban trees should be on a three- to five-year pruning cycle to maintain good form and hazard reduction. Adequate protection of desirable trees around construction sites is essential.

Chemical control of the red oak borer is not very practical and should only be considered under the most high hazard situations; a few beetles are not too damaging, while mass attacks are difficult to treat. Application timing is very critical. Red oak borer larvae control is best when insecticides are applied during the period of time when eggs are being deposited in late July and early August of even numbered years. Insecticide coverage of the entire tree trunk is critical to get satisfactory control. Even with good application, a significant risk exists that control will not be complete. The insecticide treatment should be made two to three times at two-week intervals. The insecticides recommended for treatment include Lorsban (chlorpyrifos, a restricted label) and formulations of permethrin, and these should be applied according to label requirements. Another option is to use a soil drench of imidacloprid or a tree and shrub insect control product produced by Bayer Advanced. Imidacloprid ( Brand name of Merit TM ) is a systemic product that is applied to the base of the tree with in the root zone. The label provides more details on usage and performance. Merit TM,  should be applied with a light application of liquid ammonium nitrate. The fertilizer provides better uptake, either as a soil drench or soil inject into the root zone.


Disclaimer:   The above  article contains pesticide recommendations that, are subject to change at any time. These recommendations are provided only as a guide. It is always the pesticide applicator’s responsibility, by law, to read and follow all current label directions for the specific pesticide being used. If any information in these recommendations disagrees with the label, the recommendation must be disregarded. No endorsement is intended for products mentioned, nor is criticism meant for products not mentioned. The Writer assumes no liability resulting from the use of these recommendations. 

No endorsement is not intended for any Products, Business or Web link mentioned in this Web site nor is criticism meant for any Products, Business or Web link not mentioned. Scenic Hills Nursery assumes no liability from use of these recommendations or information derived from this Web site. 

Mating pairs as the emerge in early June       (Joe) Herbert A Pase III

Exit wounds associated with Slime Flux Robert L Anderson

Male   Left    -- Female Right
James Solomon


James B. Hanson

Exit holes
Timothy Haley

Stand damage in Red Oak Mott  
Gerald J. Lenhard


Grown over attack scars on Live Oak 
James Solomon


Solomon, J. D. 1995. Guide to Insect Borers in North America Broadleaf Trees and Shrubs. Agriculture Handbook 706. Washington, D.C., U.S. Department of Agriculture, Forest Service.

Authors: Donald R. Johnson, Extension Entomologist, Frederick M. Stephen, University Professor, Department of Entomology
Tamara Walkingstick, Extension Forester.

Contact: cell: 830.257.8871
                     Jim Rediker - Nurseryman -  Arborist  - TDA Certified

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