In the past, the common stalk borer, Papaipema nebris, has not been a major pest of corn in Nebraska. Stalk borer damage in corn commonly is confined to occasional plants in the first few rows near field margins, fence rows, grass terraces and waterways.
In addition to attacking corn, this insect attacks over 100 other species of plants, including ornamentals, broadleaf weeds and grasses. It may feed on soybeans as well, but is not an economically important pest of that crop.
Understanding the common stalk borer life cycle and behaviour is critical to selecting management practices to reduce its damage in corn.
Life History :
Female stalk borer moths lay their eggs primarily on grasses such as smooth brome or on ragweed in late summer and early fall. The moths tend to lay eggs singly or in groups under sheaths and in folded or rolled leaves.
Egg laying sites usually are located in fence rows, terraces and waterways, but can be throughout a crop field if preferred hosts are available.
Eggs overwinter and hatch in late April or early May. Larvae bore into the stalks of grasses or other hosts such as ragweed, and begin feeding. As they become larger or if the plants are mowed or burned down with herbicides, the stalk borers migrate into adjacent corn plants to complete their development.
In some cases, if an appropriate weed host is not available when eggs hatch, stalk borers may begin feeding on corn directly. Corn that is between the two- and eight-leaf stages can be attacked by the migrating stalk borer larvae. Larvae develop through seven to 10 instars, or stages, in about 10 weeks. Pupation occurs in the soil and moths emerge in August, September and early October. There is a single generation each year.
Description:
The stalk borer adult is a dull, greyish-brown moth that commonly has several white or silver spots in two rows across the front wings. There is a faint whitish line across the wing near the outer edge.
The hind wings are dull brownish-grey. The moths wingspan is approximately 1 to 1 1/4 inches. Common stalk borer larvae are distinctive in appearance. Young larvae (Figure 1a) are brownish purple and have three prominent longitudinal white stripes at the front and rear ends of the body.
The stripes are interrupted at mid-body by a solid dark purple to black area on the third thoracic segment and first three abdominal segments. Fully grown larvae do not have these characteristic markings, being uniformly dirty grey (Figure 1b). Fully grown larvae can be 1 1/2 to 2 inches long.
Damage:
Stalk borer larvae injure corn plants in June and early July. They feed on leaves in the whorl and then tunnel into the stalk (Figure 2), or they burrow into the base of the plant and tunnel up through the centre of the stalk. Leaf feeding alone does not cause economic damage.
Tunnelling into the stalk can result in deformed or stunted plants which may not produce an ear. Severely damaged plants can die. Plants attacked at earlier growth stages tend to be more severely injured. A single stalk borer larva may attack more than one plant if the first plant does not support the larva as it increases in size.
Damage caused by feeding in the whorl will first show irregular rows of holes through the unfolding leaves. These irregular rows of holes will be much larger and more ragged than those caused by whorl feeding of first generation European corn borer larvae.
In severe cases an infested plant will have a very ragged appearance, with abnormal growth habits such as twisting, bending over or stunting. If the feeding injury to the central part of the plant is severe enough, the whorl will appear dead while the outer leaves are green and apparently healthy.
This condition is commonly called “dead heart.”
Conservation Tillage and Stalk Borer:
Conservation tillage and stalk borer incidence are related in two ways. Poor weed control in conservation tillage and no-tillage cropping systems may result in late season survival of grass and broadleaf weeds.
If suitable grasses or broadleaf weeds are present in crop fields in late summer and fall, the moths will deposit their eggs on these plants and the infestation of stalk borer may extend throughout the entire field.
Also, if a stalk borer infested cover crop or an existing weed infestation is chemically ?burned down? after planting, surviving larvae are forced to leave their original host, and will attack nearby corn.
Information Sourced From:
University of Nebraska–Lincoln
