Baute Bug Blog

Since my blog entry last week where I mentioned that we hadn’t found WBC feeding in dry beans yet, my crew as well as reps who have been sending photos in have found WBC pod feeding in dry bean fields at a few locations across the province.  To date, sites known to have WBC pod feeding include: Talbotville and Dutton (Elgin County), Dublin (Perth County), a few fields in Northern Huron County (nearest towns not known at this time) and Belleville (Hastings County).  I am sure that more will be found this week or next.

WBC pod feeding from Dublin

Pod Mined by WBC

Seed inside pod fed on by WBC

I recognize that it is a challenge to figure out if it is actually WBC feeding or not.  I am finding more European corn borer in beans then expected.  But the good thing is that ECB tends to leave a lot of frass just outside of the hole they made to enter the pod and you can sometimes even find them inside the pod.  Corn earworm is also doing some of the pod feeding.  The important thing to do is to open up pods that have holes going directly into the pod and look for feeding on the seeds.  If there is some seed feeding and no culprit present to point the finger at, it COULD be WBC.  WBC feed at night in dry beans so you are not likely to ever get a chance to see the WBC larvae.

If you are finding pods with holes in them on more than just a few plants in the field, we do recommend spraying if the crop is less than 21 days to harvest.  If it takes you an hour to find just a couple of pods with feeding, then that field is probably safe but scout it again later that week to see if pod feeding has increased.  Matador is registered for control.  Don’t spray at the heat of the day as temps above 25 degrees can decrease the products efficacy.  Days to harvest interval for Matador on dry beans is 21 days and for snaps and green beans it is 7 days to harvest.

I’ve been in a lot of dry bean fields this week, mainly in Huron County.  And I will admit that in a few fields, it was tough to sort out what was causing the damage. But so far, there are only one or two sites out of all of the ones I scouted that have even come close to having suspicious feeding that could be attributed to WBC.  I say “could” though as I am still on the fence with these two sites since I have two additional culprits that could be doing some or all of the pod feeding.

What is making it difficult is that there are a lot of defoliating insects out there this year that are making holes in the leaves and even scars on the surface of the pods.  This makes it tough to truly identify what is WBC feeding and what is from the others.  So you really can’t rely on foliar feeding to ID plants with WBC on them.  I am glad I had a sweep net with me to help me sort out some of the issues.  Both green cloverworm and redheaded flea beetles are in high numbers this year and are hacking at the leaves.

Defoliation by slugs, redheaded flea beetles and green cloverworm in dry beans

As for pod feeding, well that is not cut and dry either.  Bean leaf beetle in particular is doing some of the pod feeding.  Their holes rarely penetrate the pod though.

Bean leaf beetle feeding on dry bean pod

Make sure to look around in the canopy for BLB adults before assuming you have found WBC feeding.    There seems to be a lot of pods out there that had BLB or grasshopper feeding early on and the holes have dried up or even healed over.

I even found a field so full of slugs in areas that I am convinced that the big holes going directly through the pods were from the slugs and not WBC.  (Sorry Ron, I know you are pretty sure slugs don’t feed on pods but every time I found a big hole going through both sides of the pod, I found slime trails on the plant and big fat juicy slugs nearby on the ground).

WBC pod feeding tends to mine directly into the pod.  Once you open up the pod you may see some feeding on the seeds.  Here are some photos from pods that were on plants that were artificially infested and caged with WBC.  Note the one pod that actually still had WBC inside it, though this is rare to find in naturally infested fields.

Pod damage on WBC infested dry bean plant

WBC inside dry bean pod on artificially infested plants

There is one more insect that I came across that can mine into the pod though.   I found European corn borer feeding on the inside of one pod.

ECB feeding inside dry bean pod

Luckly it was still in the pod making it easy to peg as the culprit.  Unfortunately WBC is usually not inside the pod or on the plant during the day so you don’t get the satisfaction of being 100% confident in your judgement.

One final thing I learned this week.  I know I told you about how the first few instars of WBC looks sort of like ECB but with obvious dark warts and hairs coming out of them on their body.  Well, the second to third instars looks completely different.

2nd to 3rd WBC instar

They still lack the broad bands behind the head but they lose the hairy warts/spots that the very young instars have and actually start to look like true armyworm without the bands on the prolegs.  Until they get a bit bigger and start to get the broad bands behind the head, it can fool you into questioning what it is.  Those stripes certainly don’t remain on the body later in their development.

If it isn’t already obvious, there is a lot still to learn about WBC.  And it doesn’t seem to be an easy insect to scout for..especially in dry beans.  I didn’t think I’d ever say this, but I like scouting for soybean aphids much more!  Those I can find and count.

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

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.