Western Bean Cutworm Scouting

Amy Timmerman, Extension Educator Author

09/13/2023 Added

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It is time to start thinking about scheduling for scouting for western bean cutworm an important pest of corn and dry beans. Larval feeding damages both crops through reduced yield and quality. In corn, direct feeding losses may be compounded by fungal infections associated with larval feeding and waste products. In dry beans, damaged or “worm-chewed” beans are a significant quality factor for both processed and bagged dry beans.

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[00:00:00.254]This is Amy Timmerman with Nebraska Extension
[00:00:03.664]and this week's extension update.
[00:00:05.494]It is time to start thinking about scheduling for scouting
[00:00:08.421]for western bean cutworm an important pest of corn and dry beans.
[00:00:12.121]Larval feeding damages both crops through reduced yield and quality.
[00:00:16.421]In corn, direct feeding losses may be compounded by
[00:00:19.764]fungal infections associated with larval feeding and waste products.
[00:00:24.335]In dry beans, damaged or “worm-chewed” beans
[00:00:28.045]are a significant quality factor for both processed and bagged dry beans.
[00:00:32.123]Western bean cutworm moths prefer to lay their eggs on corn plants
[00:00:35.763]when they are approaching tassel emergence,
[00:00:37.953]as the tassel is the preferred food source for newly hatched
[00:00:40.763]Western bean cutworm larvae.
[00:00:43.143]A match between the flight of the moths and the late whorl to
[00:00:46.336]early tassel stage of corn can result in high levels of infestation.
[00:00:50.794]Western bean cutworm has one generation per year
[00:00:54.114]with moth emergence usually beginning in early July.
[00:00:57.182]The emergence date can be predicted by
[00:00:59.712]calculating growing degree days.
[00:01:02.002]Starting heat unit accumulations on May 1,
[00:01:05.012]using a base air temperature of 50°F,
[00:01:07.412]growing degree days for 25 percent moth emergence is 1,319,
[00:01:14.215]50 percent is 1422, and 75 percent is 1536.
[00:01:21.449]Overall, the estimated dates for Western bean cutworm flight
[00:01:24.945]in 2023 are similar to those from 2021and 2022,
[00:01:30.301]although some areas have predicted earlier flights
[00:01:33.391]compared to last year (such as Ainsworth and Concord, Nebraska).
[00:01:37.051]For Ainsworth 25% flight is predicted to occur around July 15th.
[00:01:43.038]Western bean cutworm eggs can be found on the upper
[00:01:45.878]surfaces of corn leaves, and the lower surfaces of dry bean leaves.
[00:01:49.688]Eggs are found in masses ranging from five to 200, with an average of 50-85.
[00:01:55.471]When first laid, the eggs will be white
[00:01:58.091]and gradually darken during the five- to seven-day development.
[00:02:01.124]Freshly hatched larvae will first eat the eggshells before consuming the host plant.
[00:02:06.530]Older larvae can be identified by two dark
[00:02:09.730]rectangular spots directly behind their head.
[00:02:12.730]Adult moths are identifiable by a white band on the anterior margin on the
[00:02:18.710]forewing followed by a white circle halfway down the wing and a
[00:02:22.280]white crescent located two-thirds down the wing.
[00:02:26.280]Western bean cutworm moths are about three-fourths of an
[00:02:29.250]inch long by 1.5 inches wide.
[00:02:32.070]It is more difficult to scout dry bean fields for Western bean cutworm,
[00:02:35.495]but pheromone traps can be used to provide an estimate of a possible
[00:02:39.495]infestation and should be installed prior to the predicted 5% flight date.
[00:02:44.399]If fewer than 700 moths are caught up to peak, there is low risk;
[00:02:48.489]if more than 700 but fewer than 1,000 moths are caught
[00:02:52.504]then there is moderate risk; and if there are more than
[00:02:56.172]1,000 moths caught then the risk if high.
[00:02:59.129]If an insecticide application is warranted,
[00:03:01.269]it should be made 10-21 days after peak flight
[00:03:05.238]in dry bean and when 95% of plants have tasseled in corn.
[00:03:09.764]For more information on insecticide options
[00:03:12.394]contact your local extension office or on the University of Nebraska–Lincoln
[00:03:16.614]Department of Entomology website at entomology.unl.edu.
[00:03:22.651]This has been Amy Timmerman with Nebraska Extension.

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Western Bean Cutworm Scouting

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