Root Collar Borer
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Hosts
Yellow-poplar. Yellow-poplar is the preferred, possibly only, host. Magnolia reported to be attacked (USDA FS 1985), but this is questionable. (It seems more likely that a related borer in magnolia, E. magnolialis Capps, was mistakenly identified as E. ostricolorella.)
Range
Probably occurs throughout the natural range of yellow-poplar in the eastern United States. Found as far north as New York and as far south and west as Louisiana and Arkansas.
Description
Adult
Typical pyralid moth with somewhat elongate rectangular forewings and wingspan of 29 to 40 mm. Forewings generally purplish brown with grayish dusting and wing tips bordered with long gray scales. Hindwings pale smoky black with fine dark marginal line (Heinrich 1965).
Egg
Dull, red, oblong, measures about 0.9 by 0.5 mm.
Larva
Newly hatched about 3 mm long, but range from 23 to 33 mm when fully grown (Hope and Pless 1979). Mature larva mostly dull white and head dark brown with heavily chitinized black areas. Prominent spiracles and anal shield of larva smoky brown (Schuder and Giese 1962). Larva with a pair of jointed legs on each thoracic segment and fleshy prolegs ending in numerous hooked spines (crochets) on abdominal segments 3 to 6 and 10; consequently, very mobile within and outside gallery.
Biology
Moths of the overwintering generation in Tennessee emerge from April 27 to June 8, with a peak in mid-May; moths of the summer generation emerge August 27 to October 10, peaking in mid-September (Hope and Pless 1979). Moths of the mid-September emergence have been caught in appreciable numbers in light traps in yellow-poplar seed orchards in Tennessee. Average lifespan of adult moths is about 8 days. Females oviposit at night in bark crevices. Eleven females studied in Tennessee laid an average of 39 eggs (Hope and Pless 1979). Eggs may be scattered over the bark up to 15 cm above ground level, and as many as 38 eggs have been observed on a tree (Hop and Pless 1979). Larval tunnels extend vertically or spirally above or below ground, seldom exceed 10 cm in length, and are about 6.3 mm in diameter. Most larval galleries are confined to the inner bark, and when they occasionally reach the wood surface, the larvae do not etch it except when forming the pupal chambers. Gallery walls and surrounding wood are stained black (Hay 1958). Small larvae are often found burrowing adjacent to old galleries; their tunnels may originate in the old-gallery cavities, and they push coarse frass into the old galleries but not to the bark surface (Hay 1958). In Tennessee, duration of overwintering broods is about 210 days, whereas summer generations are completed in as few as 91 days. Mature larvae cut emergence holes through the bark and cap them with bark particles and silklike materials. Larvae then return to pupal chambers in the inner bark, spin cocoons, and pupate for about 28 days. There are two complete generations from Tennessee southward and one generation per year in its northern range.
Injury and Damage
Injury is often difficult to detect because most attacks are in a relatively narrow zone at the tree base, from about 16 cm above ground to about 7 cm below. Trees from about 3 cm diameter at root collar to sawlog size may be attacked. Burrows in seedlings and saplings often spiral around the root collars. Recent larval attacks on vigorous trees may be accompanied by black ooze and frass from entrance holes (Hay 1958) and on heavily infested trees, bark just above the soil line may be loose, cracked, and appear fire scorched (Schuder and Giese 1962). Because larval burrows are entirely in the succulent inner bark and cambium, they can be observed easily by cutting away the outer bark. White, loosely spun cocoons may also be observed in larval burrows. Numerous small exit holes, made by pre-pupal larvae for the adults' emergence, can be found at the bases of infested trees, but no empty pupal cases (skins) protrude from the holes, as they do with some wood-infesting moths. Another symptom of heavy infestation is a gradual yellowing of foliage and crown dieback. Open-grown trees, such as those in seed orchards, are particularly susceptible. This borer was not recognized as an economic pest until 1954, when it was reported killing yellow-poplars, particularly trees larger than 25 cm in diameter, on a 2,228-ha timber tract in Kentucky (Hay 1958). Considerable dieback and mortality of yellow-poplars has been reported in northern Indiana woodlots (Schuder and Giese 1962). Also, extensive borer damage was found in 2.5-cm-diameter yellow-poplar grafting stock in seed orchards; as many as 10 larvae were observed in some trees (Churchwell 1966). A canker disease-Fusarium solani (Martins, [Appel and Wollenweber])--associated with borer damage killed 19, 22, and 50% of the high-value trees in three west Tennessee seed orchards (Hope and Pless 1979). When attacks occur on the bole, callus tissue and ingrown bark produce small defects in the wood (Hay 1958). However, because few attacks occur above stump height, degrade is not a serious problem. Moreover, most defects in logs can be slabbed off or peeled away in veneer, and the result is minor value loss in wood products.
Control
In Tennessee studies, the hymenopterous parasites Microcentrus delicatus Cresson and Venturia nigricoxalis (Cushman) detroyed 18% of the overwintering brood and 36% of the summer brood (Hope and Pless 1979). Studies in a large timber tract in Kentucky showed that nearly every infested tree had signs of woodpecker predation (Hay 1959). In yellow-poplar timber stands where all heavily infested, weakened, and dying trees were removed in summer salvage cuts, the broods in stumps completed development and moved to uninfested residual trees (Hay 1958). Thus, brood-tree salvage cuts have not controlled this borer. However, spraying the basal trunk with oil-based residual insecticides has provided good control of established borers and prevented new attacks (Hay 1958, Schuder and Giese 1962). Insecticides recommended for peachtree borers have also provided effective control in yellow-poplar seed orchards (Churchwell 1966). Fumigants used in sawdust mounds around the root collars have also provided good control (Hope 1978). Systemic insecticides and sticky-trap treatments generally have been ineffective.
References
Solomon, J.D. 1995. Guide to insect borers of North American broadleaf trees and shrubs. Argic. Handbk. 706. Washington, DC: U.S. Department of Agriculture, Forest Service. 735 p.
