LESSER CORNSTALK BORER: Elasmopalpus lignosellus, Pyralidae

ADULT: Small, narrow-winged moths 1/2 to 5/8 in. long. Females are covered with mostly gray to grown and reddish shiny scales. Males are pale yellow to medium brown with wings bordered with band of darker scales. Adults fly quickly when disturbed in the field, often landing on the soil several yards away.  Males are easily spotted against the darker organic soils.

EGG: Creamy green eggs that become pink to red are deposited singly or in small groups on the soil surface or directly on the stem near the soil surface. Temperature greatly effects development.  Larvae emerge in 18d at 64 degrees F, but in less than 3 d at 91 degrees F.

LARVA: Medium sized caterpillar reaching 1/2 to 5/8 in. long. Larvae are patterned with alternating narrow transverse bands of maroon and aqua blue over a cream base. They hide and feed at base of corn stalks from narrow soil-covered silken tubes 1/4 to 1/2 in. beneath soil surface.  Larvae have three pairs of true legs and five pairs of prolegs.  Larvae are very active when disturbed. They complete development in 17 to 42 d.

PUPA: The greenish (becoming brown) pupae surrounded by a flimsy silken cocoon are found in soil. Adults emerge in 10 to 24 d.

GENERATION TIME: 32 to 84 d.

DAMAGE: Larvae bore into the corn stem just below the soil surface, or into larger brace roots. They feed up and down the stem. Young plants exhibit severe drooping of youngest two to three leaves prior to death. Surviving plants often develop several suckers and are bushy and stunted. Suckers usually do not produce marketable ears. Infestations can cause severe stand loss usually in irregular shaped patterns in the field. Damage is usually more severe during dry, warm periods.  Larvae may move down a row to kill several seedlings before completing development.

CONTROL: Natural enemies are not thought to have a significant effect on lesser cornstalk borers (LCB) due to their subterranean habits, silken feeding tubes and sporadic nature.  LCB tend to be worse in drier years and on well-drained soil.  However, they can cause severe damage to sweet corn on heavy organic soils planted throughout the year. Wet, cool growing conditions increase their mortality and greatly reduce their developmental rates. While it can be difficult to predict when and where the pests will strike, certain plant rotations can result in a much higher probability of infestations.  Corn planted following corn, sorghum, small grains, sugar cane, beans, peanuts, or too quickly behind recently turned weedy fields can predispose a crop to damage.  LCB does very well on nutsedge and corn planted behind sugar cane infested with these weeds can suffer severe damage. Pheromone and black light traps can be used to monitor adults. Host plant resistance is probably the best strategy for LCB control in the future. Resistance has been noted in lines tested at CIMMYT in Mexico. Cultivation of fields several weeks in advance of planting is advised to allow for decomposition of the plant residues and completion of LCB development.  Effectiveness of chemical control is often highly variable due to the nature of the pest. Chemical control efforts can be maximized by estimating the potential for damage based on adult monitoring, surrounding crops and previous field history. In fields with a high potential for LCB infestation, at-plant pesticide application should be considered to reduce damage. Unfortunately, by the time field infestations are observed in corn, damage to the crop has already occurred. Post-emergence applications applied as soon as damage symptoms appear can limit additional damage, but may be too late to prevent economic losses.  Post-emergence applications work best when banded over the rows and lightly incorporated into the soil around the plants. Formulations, rates, and pre-harvest intervals of insecticides labeled for stalk borer control in Florida are listed below for sweet corn (Table 1) and field corn (Table 2).