Western Bean Cutworm Scouting Holt Boyd Extension Podcast

Western Bean Cutworm Scouting - July 6, 2023 - Amy Timmerman - Extension Educator

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• [0:00] This is Amy Timmerman with Nebraska Extension
• [0:03] and this week's extension update.
• [0:05] It is time to start thinking about scheduling for scouting
• [0:08] for western bean cutworm an important pest of corn and dry beans.
• [0:12] Larval feeding damages both crops through reduced yield and quality.
• [0:16] In corn, direct feeding losses may be compounded by
• [0:19] fungal infections associated with larval feeding and waste products.
• [0:24] In dry beans, damaged or “worm-chewed” beans
• [0:28] are a significant quality factor for both processed and bagged dry beans.
• [0:32] Western bean cutworm moths prefer to lay their eggs on corn plants
• [0:35] when they are approaching tassel emergence,
• [0:37] as the tassel is the preferred food source for newly hatched
• [0:40] Western bean cutworm larvae.
• [0:43] A match between the flight of the moths and the late whorl to
• [0:46] early tassel stage of corn can result in high levels of infestation.
• [0:50] Western bean cutworm has one generation per year
• [0:54] with moth emergence usually beginning in early July.
• [0:57] The emergence date can be predicted by
• [0:59] calculating growing degree days.
• [1:02] Starting heat unit accumulations on May 1,
• [1:05] using a base air temperature of 50°F,
• [1:07] growing degree days for 25 percent moth emergence is 1,319,
• [1:14] 50 percent is 1422, and 75 percent is 1536.
• [1:21] Overall, the estimated dates for Western bean cutworm flight
• [1:24] in 2023 are similar to those from 2021and 2022,
• [1:30] although some areas have predicted earlier flights
• [1:33] compared to last year (such as Ainsworth and Concord, Nebraska).
• [1:37] For Ainsworth 25% flight is predicted to occur around July 15th.
• [1:43] Western bean cutworm eggs can be found on the upper
• [1:45] surfaces of corn leaves, and the lower surfaces of dry bean leaves.
• [1:49] Eggs are found in masses ranging from five to 200, with an average of 50-85.
• [1:55] When first laid, the eggs will be white
• [1:58] and gradually darken during the five- to seven-day development.
• [2:01] Freshly hatched larvae will first eat the eggshells before consuming the host plant.
• [2:06] Older larvae can be identified by two dark
• [2:09] rectangular spots directly behind their head.
• [2:12] Adult moths are identifiable by a white band on the anterior margin on the
• [2:18] forewing followed by a white circle halfway down the wing and a
• [2:22] white crescent located two-thirds down the wing.
• [2:26] Western bean cutworm moths are about three-fourths of an
• [2:29] inch long by 1.5 inches wide.
• [2:32] It is more difficult to scout dry bean fields for Western bean cutworm,
• [2:35] but pheromone traps can be used to provide an estimate of a possible
• [2:39] infestation and should be installed prior to the predicted 5% flight date.
• [2:44] If fewer than 700 moths are caught up to peak, there is low risk;
• [2:48] if more than 700 but fewer than 1,000 moths are caught
• [2:52] then there is moderate risk; and if there are more than
• [2:56] 1,000 moths caught then the risk if high.
• [2:59] If an insecticide application is warranted,
• [3:01] it should be made 10-21 days after peak flight
• [3:05] in dry bean and when 95% of plants have tasseled in corn.
• [3:09] For more information on insecticide options
• [3:12] contact your local extension office or on the University of Nebraska–Lincoln
• [3:16] Department of Entomology website at entomology.unl.edu.
• [3:22] This has been Amy Timmerman with Nebraska Extension.