Common Stalk Borer Holt Boyd Extension Podcast

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Common Stalk Borer - June 8, 2023 - Amy Timmerman - Extension Educator

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• [0:00] I am Amy Timmerman with Nebraska Extension and this week's Extension update.
• [0:04] Scouting for common stalk borer larvae in corn should start in the next 1to 2 weeks.
• [0:09] Stalk borers are an occasional pest of corn in Nebraska.
• [0:13] Stalk borer damage in corn commonly is confined to plants in the first few rows
• [0:16] near field margins, fence rows, grass terraces and waterways.
• [0:20] In addition to attacking corn, stalk borers attack over 100
• [0:24] other species of plants, including ornamentals,
• [0:27] garden vegetables, broadleaf weeds, and grasses.
• [0:30] They may feed on soybeans as well, but they are not an economically
• [0:33] important pest of soybeans.
• [0:35] Female stalk borer moths lay their eggs primarily on
• [0:39] grasses such as smooth brome or ragweed in late summer and early fall.
• [0:43] Small grains such as rye or wheat
• [0:44] planted as a cover crop may also be a potential egg laying site.
• [0:49] Egg-laying sites usually are in fence rows, terraces, and waterways,
• [0:52] but can be found throughout a field if preferred hosts are available.
• [0:56] Eggs overwinter and hatch in late April or early May.
• [1:00] Larvae bore into the stalks of grasses or other hosts
• [1:03] such as ragweed and begin feeding.
• [1:05] As they become larger or if the plants are mowed,
• [1:08] terminated mechanically or burned down with herbicides,
• [1:11] the stalk borers migrate into adjacent corn plants to complete their development.
• [1:15] In some cases, if an appropriate weed host
• [1:18] is not available when eggs hatch, stalk borers may begin feeding directly on corn.
• [1:23] Corn between the two- and eight-leaf stages can be attacked by the
• [1:26] migrating stalk borer larvae.
• [1:29] Larvae develop through seven to 10 instars, or stages, in about 10 weeks.
• [1:33] Pupation occurs in the soil and moths emerge in August, September and early October.
• [1:38] There is only a single generation per year.
• [1:41] Common stalk borer larvae are distinctive in appearance.
• [1:44] Young larvae are brownish-purple and have three prominent longitudinal
• [1:48] white stripes at the front and rear ends of the body.
• [1:51] The stripes are interrupted at mid-body by a solid dark purple to black area
• [1:56] on the third thoracic segment and first three abdominal segments.
• [2:00] Fully grown larvae do not have the characteristic markings
• [2:04] and are uniformly dirty gray in color.
• [2:06] Full grown larvae can be 1 1/2 to 2 inches long.
• [2:09] Stalk borer larvae injure corn plants typically in late May-June.
• [2:15] They feed on leaves in the whorl and then tunnel into the stalk,
• [2:18] or they burrow into the base of the plant
• [2:20] and tunnel up through the center of the stalk.
• [2:22] Leaf feeding alone does not cause economic damage.
• [2:26] Stalk borers hatch and migration to new hosts
• [2:28] can be predicted using degree days.
• [2:31] Based on research at Iowa State University,
• [2:34] stalk borer egg hatch begins at about
• [2:36] 575 degree days and ends at 750 degree days.
• [2:40] We begin scouting corn when 1,300-1,400 DD have accumulated.
• [2:49] This corresponds with the beginning of larvae moving out of grassy hosts.
• [2:53] The determine of the needs of treatment
• [2:57] when we are at 1,400-1,700 degree days have accumulated.
• [3:01] As of today, June 8th we are currently at 1,252 degree days which indicates
• [3:07] that stalk borer larvae will begin moving into corn the next 1 to 2 weeks
• [3:12] and that scouting should begin.
• [3:15] Making management decisions on that corn is not until we hit
• [3:19] 1,400-1,700 degree days of accumulated degree days.
• [3:24] You can receive updated degree data daily.
• [3:27] It's available at Iowa State University mesonet.
• [3:30] Just google that and you will be able to find the information.
• [3:34] Refer to Economic Threshold Tables
• [3:36] and Management Options are available at cropwatch.com or
• [3:39] reach out to your local extension office for more information.
• [3:42] This has been Amy Timmerman with Nebraska