Western Bean Worries

Cutworm Damage Can Cause Mold, Grain Quality Issues

Pam Smith
By  Pam Smith , Crops Technology Editor
Connect with Pam:
Western bean cutworm does a fair amount of damage deep into the ear and could cause mold and quality problems. (DTN photo by Pamela Smith)

DECATUR, Ill. (DTN) -- Peel back a few husks if you live in western bean cutworm country.

Entomologists and farmers are reporting higher-than-normal numbers of these caterpillar pests in the ears of both Bt and non-Bt corn hybrids this year. The kernel damage can open the ear up to molds and storage quality problems.

Ear tip feeding is the most obvious symptom of western bean cutworm, but they may also tunnel into the bottom of the ear. Although it's too late to do a rescue spray, knowing which fields have infestations should influence harvest decisions.


The western bean cutworm is a native of North America that has recently expanded its range eastward from the Great Plains region. After its initial discovery in southeastern Iowa in 2004, it was found in western Illinois and in northwestern Indiana in 2006.

Extension entomologists in Indiana, Michigan, Pennsylvania and Ohio have all issued western bean cutworm warnings this fall. Michigan State University entomologist Christina Difonzo said in her alert that damage is being found in Bt and non-Bt corn hybrids.

Understanding which traits are meant to control WBC is important. Bt proteins that kill European cornborer do not give 100% control of western bean cutworm, Difonzo reminded readers in her recent bulletin.

"Cry1Ab (Yieldgard) and Cry1A.105 plus Cry2Ab2 (Double Pro) are not effective," she reported. "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."

The Cry1F protein is known as Herculex 1 and is also found in Herculex Xtra. The Herculex trait is found in most Acremax (AM), Instrasect and TRIsect packages. It's also the above-ground component in Smartstax and many Agrisure E-Z Refuge corn hybrids.

Because the Bt protein must be ingested by the larvae before they die, minor damage on the ear of Bt-expressing hybrids has long been common. This light feeding usually results in some scarring or scraping on the tops of kernels. The type of feeding being found this year is much more severe, and larvae are not dying.

The Vip3A trait (found in some Agrisure hybrids and AcreMax Leptra) is a Bt protein targeting secondary caterpillar pests, and it should still be effective against western bean cutworms, Difonzo said.

For heavily infested fields, Difonzo recommends the following steps:

· Report highly infested Cry1F fields to seed dealers and university entomologists like Difonzo. If you have a Vip3A field with unexpected damage from western bean cutworms, report it immediately as well.

· If possible, harvest infested fields as silage to avoid drying costs and lowered grain quality problems.

· Run the grain from problem fields over a screen before storing it to remove damaged kernels.

· Dry the grain down rapidly, to avoid pathogen growth and mycotoxin development.

· Never mix grain from infested fields with good quality grain. "Better yet, don't store western bean cutworm damaged grain at all, if possible," Difonzo concluded.

For more information, see this alert from Purdue University: http://bit.ly/…, and this fact sheet on western bean cutworm: http://bit.ly/….

You can read Difonzo's complete article on the pest here: http://bit.ly/….

Pamela Smith can be reached at pam.smith@dtn.com.

Follow Pamela Smith on Twitter @PamSmithDTN.


Pam Smith