Author: Dr. Steve L. Brown, Dr. Will Hudson, University of Georgia
The larva of the lesser cornstalk borer (LCB) is dark-colored with purple bands around its body. Full grown larvae are about 3/4" long. When disturbed they flip about very rapidly.
LCBs have a wide host range but have the greatest economic impact on corn, small grains, soybeans, peanuts, beans and peas.
Larvae tunnel into the crown of host plants, severely weakening large plants and often killing young seedlings. On peanuts, LCBs will feed on any portion of the plant that contacts the soil including limbs, pegs and pods. Peanut pods damaged by this insect have been shown to have significantly more aflatoxin contamination than undamaged pods.
LCBs overwinter as larvae or pupae in the soil. Adult moths emerge in the spring and lay eggs on the host plants. Larvae feed for about 3 weeks spinning silken tubes near the soil surface for protection.
Outbreaks of LCB occur during periods of hot, dry weather. Rainfall or irrigation will greatly reduce the threat of LCB damage. Liquid insecticides directed at the base of host plants or granules applied to the soil can be effective but hot, dry conditions often reduce the longevity of registered insecticides.
Originally compiled from
Black locust, dogwood, tupelo, sycamore, pine, redcedar, Arizona cypress, and baldcypress. Corn, peanuts, and many other legumes and grasses are attacked, but plants in the grass family are preferred; attacks trees only ocassionally (Dixon 1982b, Luginbill and Ainslee 1917).
Throughout the southern half of the United States but most damaging in sandy soil along the south Atlantic and Gulf Coasts. Also occurs throughout Central and South America (Luginbill and Ainslee 1917).
Brownish moth with wingspan of 17 to 25 mm (Luginbill and Ainslee 1917). Forewings narrow and elongate with oblique distal margins; yellow ochre to light brown in males and dark brown in females. Hindwings whitish with gray to brown anterior and distal margins. Head brown to black.
Oval, 0.7 mm long by 0.2 mm wide, with sculptured surface; pale green when first deposited, becoming iridescent crimson at maturity.
Greenish brown and about 16 mm long when mature. Head and cervical shield shiny brownish black; body pale green with longitudinal, somewhat broken white and purple stripes.
Pale yellowish green initially, gradually becoming dark brown, with six hooked spines on abdomen tip, and about 8 mm long.
Moths emerge during early June in southern Georgia and are caught almost continually in light traps through Augus (Leuck 1966). Average life of adults is 10 days, and each female deposits about 125 eggs. Eggs are generally deposited singly on the upper and lower sides of leaves, at any point along the stem, and in soil just below the surface with grains of sand adhering to them. Eggs hatch within a week, and early-instar larvae mine lower branches or begin to feed on stem and roots below the soil surface (Dixon 1982a). Larvae construct radiating tubelike shelters of silk, soil, and excrement near the root collar just below the soil surface. Feeding by larvae on woody tree seedlings is characterized by surface or subcortical burrowing and girdling and often results in gall-like swellings and callus tissue around the feeding site (Snyder 1936). Larvae pass through six instars, and total larvae development requires 13 to 24 days (Dupree 1965, Leuck 1966). The pupal stage is 8 to 10 days. By late summer, most life stages are present in infested plants as generations overlap. The winter is passed in either the larval or pupal stage in soil and soil litter. It completes two to four generations per year (Dixon 1982b).
Injury and Damage
The first sign of infestation in forest tree nurseries is wilting foliage. As seedlings begin to die, they may remain upright or fall over. Removing soil from around the base of the seedlings reveals larval burrows girdling the stem and gall-like swelling and callus tissue at wound sites. Sometimes, seedlings are severed just below ground (Snyder 1936). Close inspection of the soil near feeding sites exposes small tubes, composed of silk and soil particles, radiating from the injured seedling. Only one larva is found in a silken tube. Larvae squirm vigorously when disturbed (Dixon 1982a). When adults are disturbed and forced to fly during daylight, they fly with short, jerky movements (Dixon 1982a). During the 1930's. 1 to 2% of the black locust seedlings in forest tree nurseries in Mississippi, Arkansas, and Louisiana and up to 10% of those in North Carolina nurseries were killed (Snyder 1936). More recently in a central Florida forest tree nursery, this borer killed about 1 million hardwood and softwood seedlings and injured as many more (Dixon 1982b). Mortality of flowering dogwood in the Florida nursery was 70% and the remaining 30% suffered injury.
Parasites are abundant (Arnaud 1978, Krombein and others 1979). In Texas, larval mortality from insect parasites ranges from 5 to 9%, and pupal mortality averages about 5% (Johnson and Smith 1981). Culturally, selected covercrop rotation, late-fall clear-fallowing, proper soil fertilization, and irrigation will help to ameliorate the factors conductive to infestation. When such practices fail, granular insecticides can be incorporated in the soil before covercrops are sown. In serious borer infestations, insecticides can be applied to nursery beds as soil drenches; this may have to be repeated several times because adequate exposure of larvae to the chemical is difficult, as they retreat into their silklined shelters when disturbed (Dixon 1928b).
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.