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Description
Brown worms with white longitudinal stripes and a distinctive
purple area in the middle of the body are often found boring
into the stems of plants, particularly ragweed, oats, and
corn. The worms are active and move rapidly when disturbed.
When full grown, they are 1 1/2 to 2 inches long. The pupa
is brown and spindle-shaped. The moth has a wing expanse of
slightly over one inch, and the forewings are brown to gray
with small white spots. The eggs are somewhat globular, ridged,and
laid in the creases of rolled or folded leaves, weeds, grasses,
and garden crops.
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Figure
1. Common Stalk Borer Adult
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Figure
2. Common Stalk Borer Pupa
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Life
History
The borer passes the winter in the egg stage. The eggs hatch
in May and the worms tunnel into nearby plants, becoming full
grown in July. They then pupate, usually just below the soil
surface, and emerge as moths in August. The moths deposit
eggs in August in weeds and grassy patches, particularly along
fencerows, ditch banks, and grass waterways. There is one
generation a year.
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Damage
This insect tunnels into the stalks of such crops as the small grains,
grasses, and corn. The unfolding leaves of corn plants often show
irregular holes where the worms damaged them while they were still
in the whorl The heads of individual grain plants turn white prematurely
in areas in small-grain fields, especially oats. Examination of
the stalk may show this pest. Other insects that hollow out the
stems of small-grain plants can cause similar symptoms.
| Feeding
occurs most frequently in rows adjacent to areas that were weedy
during the previous August. Damage from this pest is usually
of little economic significance. |
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Figure
3. Common Stalk
Borer in Wheat Stem
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Figure
4. Common Stalk Borer in Corn Stalk
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Scouting
Procedures
Estimate the infestation by checking 20 plants in each of five
locations. Check around border rows of conventional tilled fields
in May-June. In no-till fields a random check throughout the
field is necessary. Chemical control is usually not very effective. |
Threshold
Guide
None established. A "rescue" insecticide treatment
may be effective if it is applied when the larvae are moving
from their weed hosts to corn seedlings. Rescue treatments applied
after the larvae have entered the plants are not effective. |
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on image for larger version
Figure 5. Common Stalk Borer Larva on Corn
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Authors:
Susan T. Ratcliffe (sratclif@uiuc.edu)
Michael E. Gray (m-gray4@uiuc.edu)
Kevin L. Steffey (ksteffey@uiuc.edu)
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