Baute Bug Blog

These next two weeks are critical for western bean cutworm scouting and management in dry beans.  Peak moth flight took place at the end of July and pod feeding is typically expected 10 to 21 days after peak flight.  Huron County is particularly at risk given the very high moth count for that county this year (over 26,000 moths so far) but all dry beans in Ontario should be scouted these next few weeks to determine if management is necessary.  Any field with pods right now are at risk.

Pod feeding by WBC (Photo Credit: Chris Difonzo. MSU)

Look in particular for holes and feeding scars starting on the pods.  There could also be some leaf feeding by the younger larvae, however unless you can actually find the larvae, it is difficult to prove that it was western bean cutworm that did the leaf feeding and not another insect.  If pod feeding is present, a spray is necessary.  Make sure that there are pods and pod feeding present as this is the best stage and timing to achieve good control of WBC.  Matador is registered on dry beans for WBC control.

DRY BEAN FIELDS WANTED FOR SPRAY TRIAL – If you find a dry bean field that has pod feeding, call me (519-674-1696) or message me on this site before you spray.  Chris Gillard and I are looking for fields with WBC to test new insecticide chemistries for registration in dry beans. We really hope to have more products in our tool box to control this insect in the future.

I am still hearing from people who are looking for WBC egg masses on corn leaves.  But unless they are scouting very late corn that is not in tassel yet, most of the WBC will already be larvae on the tassel or more likely in the ear.  So focus on scouting the ears and tassels now.

But there are other larvae that you might come across so I thought I’d help show the differences between them all.   Especially when they are small since it is harder to see their distinguishing features.  Here are some pics and helpful hints to determine which pest you are finding.   Click on each image to get a larger photo to really see the distinguishing markings.

Western bean cutworm

Young WBC larvae can be misidentified as ECB because of the spots they have.  Older larvae can be misidentified as CEW because of they have the same coloured face.

2nd instar WBC larvae on the tassel (Photo credit: Chris DiFonzo, MSU)

The first two instars are the hardest to ID.  They actually don’t have the two broad bands behind their head yet.  And they have spots or warts that have hairs coming out of them which they lose later as they grow.  Also, the tiny 1st and 2nd instars larvae crawl like inchworms, where they walk their back legs up close to their front legs, creating a loop in their body.  Can be easily mistaken for ECB at this young stage.

Once WBC are in their 3rd instar, they stop walking like inchworms.  And they lose their spots and finally have their broad bands behind their heads.  Their heads are also finally more of a light brownish orange  in colour.  Some will also have a dark band running along the side of their bodies but not all of them do.

Full Grown WBC larva

European corn borer

Young ECB larvae.

Young ECB larvae feed are too small to feed on anything but leaf or tassel tissue.  Once they grow larger they will mine into the midrib and stalk.  Young instars still have the distinct black head but the spots on their body are barely noticeable.  WBC spots or warts are more obvious.

Later ECB instar in corn ear

It is the older (larger) ECB instars that you will find into the ear.  Larvae mainly enter via the shank of the ear from the stalk of the plant.  They make their way through the shank to the ear tip before exiting the shank to graze the surface of the kernels.   Spots on their bodies are easier to see once they are this size.

Corn Earworm

CEW really vary in colour from various shades of green to brown.  But their heads are usually a light brown with a network of veins running across its face.  A key feature is the spines or hairs that are coming out of the warts along the side of their body.  They also have stripes that run along the side of their body.

Western bean cutworm and Corn earworm heads. Note the broad bands behind WBC head and the warts on the CEW. (Photo Credit: Marlin Rice)

Fall Armyworm

The only other larvae that you could come across and question if it is WBC is fall armyworm.  However these have darker heads with a white upside down Y along its face.  Also, their stripes along their body are quite easy to see.  They too have hairs sticking out like CEW have but CEW have a much lighter face than fall armyworm.

Fall Armyworm

I was sent a message today from Deb Campbell of Syngenta Seeds, that they are finding fall armyworm in corn in Grey, Perth, Oxford, Huron and Simcoe counties.  Infestations are low and the larvae are small but it is something to keep an eye on.  There could be fields with heavier infestations.

Also, both Michigan and Ohio are reporting finding incredibly heavy infestations of second generation true armyworm in mixed forages.  In Michigan it is a combination of true armyworm and variegated cutworm.  Grasses in these fields are being eaten down to the midrib of the plant.   Haven’t heard of any infestations like this in Ontario this year but keep an eye out for this.

It hasn’t been since 2002 that we have experienced this low of levels of soybean aphids.  Cross my fingers and knock on wood but I think we are going to get through the season without a problem.

That said, spidermites are starting to pop up in fields, particularly where it is starting to get a bit dry.  Scout perimeters and keep an eye out for plants and leaves that are bronzing or look sandblasted.  It is too easy to miss the mites and suffer a serious yield loss because of it.  Even the aphids don’t like to live on the mite infested plants!

Based on scouting observations and trap counts so far, it looks like we have finally passed the peak for western bean cutworm moth activity.  Egg masses are difficult to find now in corn which tells us that the moths are no longer interested in laying eggs in that crop…unless of course there is an extremely late planted corn field in the area.  Then those fields could still be at risk.

But for the most part, scouting needs to focus on the bean crop now.  Do not spray fields based on moth catches or egg masses.  Wait until you see pod feeding by WBC so that you are targeting the larvae that are actually doing the damage.  It will result in much more effective control.  There was a CropPest newsletter article that went out last week with some of my previous blog entries but also has a good picture of what early pod feeding looks like by Chris Difonzo. Click here to see the article and the photo.

Again Matador is registered for the bean crop and Matador and Decis are registered for the corn crop.  No other products are registered for control of western bean cutworm at this time.  We do have permission from CFIA to spray the refuge with insecticide if it reaches threshold for western bean cutworm, as long as the adjacent Bt corn field is also sprayed at the same time.