Common Stalk Borer
Scouting for common stalk borer larvae in corn should start in the next 1-2 weeks. Stalk borers are an occasional pest of corn in Nebraska. Stalk borer damage in corn commonly is confined to plants in the first few rows near field margins, fence rows, grass terraces and waterways.
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[00:00:00.224]I am Amy Timmerman with Nebraska Extension
and this week's Extension update.
[00:00:04.435]Scouting for common stalk borer larvae in
corn should start in the next 1to 2 weeks.
[00:00:09.385]Stalk borers are an occasional
pest of corn in Nebraska.
[00:00:13.105]Stalk borer damage in corn commonly is
confined to plants in the first few rows
[00:00:16.875]near field margins, fence rows,
grass terraces and waterways.
[00:00:20.935]In addition to attacking corn,
stalk borers attack over 100
[00:00:24.094]other species of plants,
broadleaf weeds, and grasses.
[00:00:30.094]They may feed on soybeans as well,
but they are not an economically
[00:00:33.566]important pest of soybeans.
[00:00:35.796]Female stalk borer moths
lay their eggs primarily on
[00:00:39.196]grasses such as smooth brome
or ragweed in late summer and early fall.
[00:00:43.196]Small grains such
as rye or wheat
[00:00:44.911]planted as a cover crop may also
be a potential egg laying site.
[00:00:49.146]Egg-laying sites usually are in fence
rows, terraces, and waterways,
[00:00:52.976]but can be found throughout a
field if preferred hosts are available.
[00:00:56.976]Eggs overwinter and hatch
in late April or early May.
[00:01:00.286]Larvae bore into the stalks
of grasses or other hosts
[00:01:03.636]such as ragweed
and begin feeding.
[00:01:05.646]As they become larger
or if the plants are mowed,
or burned down with herbicides,
[00:01:11.176]the stalk borers migrate into adjacent
corn plants to complete their development.
[00:01:15.176]In some cases,
if an appropriate weed host
[00:01:18.126]is not available when eggs hatch, stalk
borers may begin feeding directly on corn.
[00:01:23.335]Corn between the two- and eight-leaf
stages can be attacked by the
[00:01:26.705]migrating stalk borer larvae.
[00:01:29.005]Larvae develop through seven to 10
instars, or stages, in about 10 weeks.
[00:01:33.447]Pupation occurs in the soil and moths emerge
in August, September and early October.
[00:01:38.797]There is only a single
generation per year.
[00:01:41.621]Common stalk borer larvae
are distinctive in appearance.
[00:01:44.916]Young larvae are brownish-purple and
have three prominent longitudinal
[00:01:48.646]white stripes at the front
and rear ends of the body.
[00:01:51.773]The stripes are interrupted at mid-body
by a solid dark purple to black area
[00:01:56.563]on the third thoracic segment and
first three abdominal segments.
[00:02:00.423]Fully grown larvae do not have
the characteristic markings
[00:02:04.013]and are uniformly
dirty gray in color.
[00:02:06.303]Full grown larvae can be
1 1/2 to 2 inches long.
[00:02:09.843]Stalk borer larvae injure corn
plants typically in late May-June.
[00:02:15.360]They feed on leaves in the whorl
and then tunnel into the stalk,
[00:02:18.510]or they burrow into
the base of the plant
[00:02:20.575]and tunnel up through
the center of the stalk.
[00:02:22.720]Leaf feeding alone does not
cause economic damage.
[00:02:26.049]Stalk borers hatch and
migration to new hosts
[00:02:28.939]can be predicted
using degree days.
[00:02:31.088]Based on research at
Iowa State University,
[00:02:34.073]stalk borer egg hatch
begins at about
[00:02:36.045]575 degree days and
ends at 750 degree days.
[00:02:40.856]We begin scouting corn when
1,300-1,400 DD have accumulated.
[00:02:49.156]This corresponds with the beginning
of larvae moving out of grassy hosts.
[00:02:53.405]The determine of the
needs of treatment
[00:02:57.380]when we are at 1,400-1,700
degree days have accumulated.
[00:03:01.356]As of today, June 8th we are currently at
1,252 degree days which indicates
[00:03:07.510]that stalk borer larvae will begin
moving into corn the next 1 to 2 weeks
[00:03:12.903]and that scouting should begin.
[00:03:15.050]Making management decisions
on that corn is not until we hit
[00:03:19.210]1,400-1,700 degree days
of accumulated degree days.
[00:03:24.610]You can receive updated
degree data daily.
[00:03:27.025]It's available at Iowa State
[00:03:30.686]Just google that and you will
be able to find the information.
[00:03:34.356]Refer to Economic Threshold Tables
[00:03:36.221]and Management Options are available
at cropwatch.com or
[00:03:39.618]reach out to your local extension
office for more information.
[00:03:42.776]This has been Amy Timmerman
with Nebraska Extension.
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