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Senior Advisor

WBC Damage - Michigan

Got this off the ole Chat ' N' Chrew this morning - Black Sand - Have you checked your corn ???


btw Backy - Remember Sept 12 - at 10 am And you can even bring that hard to get along Wife of yours - lol



Check corn now for western bean cutworm damage before harvest

Alert! There have been numerous reports of high western bean cutworm infestations and damage in south and central Michigan, including in Bt corn hybrids.

Posted on August 26, 2016 by Christina DiFonzo, Michigan State University Extension, Department of Entomology








Kernel damage and ear rot on non-Bt corn. Damage along the side of the ear is characteristic of western bean cutworm feeding. Photo: Chris DiFonzo, MSU.
Kernel damage and ear rot on non-Bt corn. Damage along the side of the ear is characteristic of western bean cutworm feeding. Photo: Chris DiFonzo, MSU.

A lot of western bean cutworm damage is being found in central and southern Michigan, in both non-Bt and Bt corn (including Cry1F). I would appreciate any observations on percent infested ears by hybrid, especially feedback on Bt hybrids with the Cry 1F Bt trait (email me at Cry1F is in Herculex 1 and Xtra; most Acremax (AM), Intrasect and TRIsect packages; in Smartstax; and Agrisure E-Z Refuge products (3122, 3220, 5122, 5222). Caterpillars will be tucked in the ear tip or between the ear and stalk; they may not be obvious at first glance unless you peel back the husk. To quote a caller from yesterday, Aug. 25, 2016, “When you walk into the field, it looks OK.”

Recall that western bean cutworms were a concern in 2008-2011 in corn and dry beans when it was colonizing the Great Lakes region from the western states. In the 2012 drought, the population tanked and biocontrol picked up for the next few years. However in 2015, numbers started to increase again. This year, flights were fairly heavy in central Michigan (a known hot spot), but also in southern counties. Damage is being reported most often in fields in areas with sandy soil, which likely increases overwintering success. Entomologists in neighboring states are reporting damage too. Up-and-down population cycles are typical of many agriculture pests.

Some people in southern Michigan may be dealing with western bean cutworms for the first time, so let’s recap a few important points.

Western bean cutworms overwinter here in Michigan (i.e., we grow our own), and seem to do especially well in areas with sandy soil. My lab found larvae overwintering as deep as 12 to 16 inches in sandy soil. Hot spots in previous years were counties along Lake Michigan, in southwest Michigan along the Indiana border, in central Michigan in Montcalm, Gratiot and Isabella counties, and in the Upper Peninsula, all areas with sandy soil.

Western bean cutworm females are attracted to pre-tassel corn for egglaying. Fields that are infested now were at that perfect stage back in late-July or early August. Larval management (a pyrethroid spray) needs to happen during and just after egg-hatch. Scouting for egg masses is relatively easy if you know what to look for. In Michigan, I recommend a lower threshold (5 percent plants infested) compared to western states. Once small larvae move down the plant and inside the husk, spraying is neither recommended nor effective. On all the pyrethroid labels under corn is this statement about western bean cutworms: “For control before the larva bores into the ear.” And late August is far too late since western bean cutworms are starting to drop to the ground to overwinter. The damage is mostly done.

Larvae usually feed in the ear tip. If the tip isn’t completely filled, yield loss can be minimal. Larvae sometimes bore into the side where the ear presses against the stalk. Again, the number of kernels eaten may only be a few. But yield loss doesn’t tell the whole story. Often, the more important impact from the feeding is the husk damage and opening of the ear. As western bean cutworms feed, they chew tissue and spew out messy frass. The open husk lets in secondary insects like sap beetles, which do the same. The result is a moist, wounded area for pathogen growth. Depending on environmental conditions, mycotoxins can then contaminate damaged grain at harvest.

Note it is too late – in time and plant stage – to spray fungicides in an attempt to prevent or “clean up” ear infections. Reduction of ear molds and mycotoxins must begin much earlier, by scouting and spraying for western bean cutworms at the optimal timing to avoid ear damage altogether.

The Bts that kill European corn borer do not give 100 percent control of western bean cutworms. Cry1Ab (Yieldgard) and Cry1A.105 plus Cry2Ab2 (Double Pro) are not effective. Cry1F is listed as giving western bean cutworm control, but it is having a tough time this year – many Cry1F hybrids are being chewed on, especially in southern Michigan. It is my opinion that it only provides suppression; bigger larvae are able to eat up ear tips regardless of the Cry1F. Vip3A (in some Agrisure hybrids and AcreMax Leptra), a Bt optimized for secondary caterpillars, should be effective against western bean cutworms.

This information is from a trial my lab did in 2010 during the western bean cutworm outbreak in Montcalm County. Cry1F hybrids had less damage and ear mold, but control of western bean cutworm was not 100 percent. (Note that these hybrids were not genetically equivalent, so yield loss is difficult to attribute all to western bean cutworm.)


Western bean cutworm control

Type of hybrid

Type of Bt(s)

Expected western bean cutworm control

% ears with feeding

% ears with ear rot

# kernels eaten per ear


Non Bt






-18 bu







-8 bu







Avg. 239 bu/ac

Smart Stax







The complete report with pictures is at “Western Bean Cutworm in Michigan: Update on corn research from 2010 (pdf),” by Michigan State University’s Chris DiFonzo and Megan Chludzinski, and MSU Extension’s Fred Springborn.

If you have a field that is heavily infested (beyond what you’d expect from the 5 percent refuge):
•Consider reporting highly infested Cry1F fields to your seed dealer so that the companies can get an idea of the scope of the problem. For sure report a Vip3A field that appears to have unexpected high damage from western bean cutworms, as this would be of great concern.
•If you have an option of harvesting an infested field as silage, that will avoid drying costs and further quality loss.
•Run the grain from infested fields over a screen before it goes into a bin to get out as many damaged kernels as possible.
•Dry the grain down as soon as possible to prevent pathogen growth and mycotoxin development.
•Never store bad grain over good, or add it to a bin with good grain. Better yet, don’t store western bean cutworm damaged grain at all, if possible.

I would appreciate your emailed observations on percent infested ears by hybrid, especially feedback on Bt hybrids with the Cry1F Bt trait. You can email me at

Dr. DiFonzo’s work is funded in part by MSU’s AgBioResearch.

This article was published by Michigan State University Extension. For more information, visit To have a digest of information delivered straight to your email inbox, visit To contact an expert in your area, visit, or call 888-MSUE4MI (888-678-3464).





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Esteemed Advisor

Re: WBC Damage - Michigan

Thanks for the heads up Ken. I scouted some of my corn this week. All of my corn was non GMO this year. I have one 63 acre sandy loam  field of early corn planted April 19th and 20th that not only got snowed on, but also had a bad infestation of asiatic garden beetle grub. I re-planted about 10 acres or so in that field due to grub damage. Then several acres of that field got hailed on in a mid June thunderstorm. To top it off I found plenty of WBC damage and ear rot in that field. I estimate the yield in that field at 120 bu give or take. Now a 35 acre clay field we planted to corn May 18th looks great! We didn't have any snow/grub/hail damage and I didn't notice any WBC damage in that field. I would estimate the yield in that field in the 180-200 bu range. I planted non GMO corn for the premium and lower seed cost. The outfit that buys the non GMO corn is a large chicken company. The problem I had this year is that the chicken outfit didn't want to contract corn for fall delivery, so I missed out on the spring price rally. I'm not sure if raising non GMO corn is worth the risk, especially if I had on farm storage and having to worry about all the ear rot that comes with WBC. Being that I sell seed for a new company that has a nice lineup of VT double pro's, I may go that route instead of non GMO. 


BTW, The wife and I would love to make it to your field day this year. It was a top notch field day last time and we really enjoyed it, but we both work our off farm jobs that day. Plus we have been picking and hauling pumpkins like crazy on our off days. 


PS. The wife says you're asking for trouble lol! 


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