Baute Bug Blog

We are nearing or at peak flight for WBC.  This is nearly 3 weeks ahead of last year.  Much of the corn crop is starting to be less attractive for them.  Late planted fields not in tassel yet will still be their target but if those are not available, then they will move on to dry beans and snap beans.  WBC will continue to lay eggs over the next two to three weeks so scouting in both corn and beans must continue.  However, scouting and monitoring in dry beans is a little more complicated.

WBC eggs and larvae are nearly impossible to find in dry beans.  They do the exact opposite of what they do in corn.  They like to lay their eggs on the underside of dry bean leaves and tend to do this on leaves that are deeper in the canopy.  Larvae do a little bit of leaf feeding but as they grow, they start to only feed at night and go after the pods to feed and mine into.  So trying to scout for these critters in dry beans is frustrating to say the least.  And thresholds established in Nebraska and other western states do not seem to work properly for dry beans grown in the great lakes region.

Instead, we recommend you take a 3 step approach.

Step 1.  Monitor traps to determine peak flight for your area. Having two traps in each dry bean field will give you an idea of when peak flight will take place.  We know that you should expect pod feeding 10-20 days after peak moth flight.  If you don’t have traps directly in your own field, at least get an idea of when traps in your area have reached peak moth flight.  Over 400 traps are monitored through the WBC trap network for Ontario and Quebec.  Trap count maps are available at: http://www.cornpest.ca/default/index.cfm/wbc-trap-network/weekly-maps-of-wbc-trap-catches/

Step 2.  Scout neighbouring corn fields that are not in full tassel yet.  As mentioned, WBC is a completely different beast in corn than in dry beans.  It is much easier to scout for WBC eggs in corn as they are quite visible and are laid on the top leaves of the plant.   If there is a corn field near the dry bean field that hasn’t fully tasseled yet, scout it instead.  Go out and scout these fields now.  Walk in 5 areas of the corn field and slowly walk by 20 plants.  Follow the helpful tips that I posted on the previous blog entries titled WBC Eggs Found in Fields in Ontario and Facts You Need to Know to Scout and Manage WBC in Corn.  If 5% of the plants inspected have egg masses on them, know that your dry bean field is also at risk.  But you still need to scout for pod feeding to accurately time your spray application (see Step 3).

Step 3.  Scout for Pod Feeding in Dry Bean Field. You can effectively manage WBC in dry beans once you have found pod feeding in your field.  Pod feeding should start 10 to 20 days after peak moth flight has been observed (Step 1).  But again, ensure that pod feeding is taking place to avoid a missapplication of insecticide in your field.  Some growers in Michigan are trying to spray for WBC in their dry bean fields now, before they even have pods present on the plants which is not the correct timing to effectively control WBC in dry beans.  Wait until there are pods present for WBC to feed on.  Spraying once pods are present, ensures that you are maximizing your chances of effectively controlling the larvae when they are about to do economic damage.  Spraying too early when pods are not present is a premature application and will result in you needing to spray again when pods need protecting.  Spraying at the correct time when feeding is prsent ensures there is a decent amount of residual to protect the crop for a week or so during the critical time.

Scout 20 plants in 5 areas of the dry bean field.  Leaf feeding may be evident but is not economic.  Inspect pods for surface feeding and entry holes.  Don’t confuse the surface feeding caused by bean leaf beetle adults.  If the bean leaf beetles are doing the damage, you should be able to easily find them in the crop.  If no bean leaf beetles are present, it is most likely WBC feeding.

Spray the crop once pod feeding has been found.  Matador is registered for WBC control in dry beans.  See the 2010 Supplement for the OMAFRA Field Crop Protection Guide for rates and recommendations.

I have heard of grower who is going to spray his corn next week because there have been a lot of WBC moths flying around.  This is not an acceptable practice.  Trap counts do not necessarily reflect what is going on in the field.  It simply tells us when to expect peak egg laying.  Scouting is the only true method to determine if these moths flying around have actually laid eggs in your field.  Case in point….Blyth has had an history of catching the most moths in the province over the past two years and yet very little damage was found in that area compared to other fields in other counties.

Thresholds are not only there to ensure that you are spending your money wisely when it is truly necessary to protect your crop from a pest but it also reduces the risk of apply insecticides when they are not needed.  I understand that time is precious but so is the environment.  Scout for eggs and make sure the pest is actually present in your own field.

I was starting to doubt my abilities to properly scout for WBC eggs, given my height.  I walked a lot of fields last year with zero success.   I was really good at finding larvae in the fall though so clearly there were eggs to be found earlier that year.  You start to feel somewhat of a hypocrite when you haven’t actually found eggs yourself and you have to tell people “how to scout for them”.

But yesterday I received word that Mike Russell, a Cargill scout, had found WBC eggs in a few fields in Norfolk County.  Desperate as we are to find eggs for research trials at Ridgetown, I quickly drove to find him.  Not only did he direct me to the field but Mike already had 10 egg masses in hand to pass on to me.  Nice job!  Going to the field myself, within a few minutes I FOUND EGGS MYSELF, making me feel much better about being so vertically challenged.   Since then, my students have also found eggs at a field in Strathroy.

Going back to the field today, I have learned a bit more about how to scout for WBC eggs and I also got a few cool pics too.

First, CROP STAGE:  It really does come down to which field is in the ideal crop stage for the moth.  They really do like to lay their eggs on plants that are not in tassel.  This particular field was already in tassel but some of the plants within the large headland were shorter and were not quite in tassel yet.  When we scouted the rest of the field and neighbouring ones that were in full tassel, eggs were not nearly as easy to find.  Even if a trap located within a corn field has caught a bunch of moths, the moths may not have selected that particular field to lay the eggs.  They are likely to look around and pick the one nearby that has not tasseled yet.  Or at the very least, has some plants less advanced than the rest of the field.

Second, RELY ON EGG SHADOWS:

Sun Shining Through Leaf to Show Shadow of WBC Egg (T. Baute, OMAFRA)

Egg mass that was making the shadow (T. Baute, OMAFRA)

Use the sun to your advantage.  If you walk slowly along a corn row with the sun in front of the plants so that it is shining light through the leaves, you can often see the shadow of the WBC eggs.  Sometimes I will admit that the shadow turns out to be bird poop but often it is actually a WBC egg mass.

Third, STINK BUG EGGS: Don’t confuse WBC eggs for stink bug eggs.

Newly hatched WBC eggs (T. Baute, OMAFRA)

Stink Bug Egg Mass Ready to Hatch (T. Baute, OMAFRA)

Once you have found a WBC egg, it is pretty obvious that they are different than stink bug eggs.  But until you do, you question what you are looking at.  Stink bug eggs are laid in a very tight geometric shape… almost honeycomb like in pattern.  They start out more yellow, are slightly bigger and somewhat barrel shaped.  With a handlens you can really see the difference.

Forth, EGG MASS LOCATION:

WBC Moth Hiding in Leaf Collar (T. Baute, OMAFRA)

Closeup of WBC Moth (T. Baute, OMAFRA)

Often we were finding egg masses on the second or third leaf from the whorl.  Usually the leaf that was the most fully expanded but also still erect at the top of the plant.  And the egg mass tended to be closer towards the leaf axil.  After finding an adult moth hiding in one of the leaf collars, I can see why we are finding the eggs too close to that collar.

Hope this helps you to find your own egg masses.  Don’t solely focus on one area of the field but get a good sense of what the population is like across the field.  And try not to get a kink in your neck.

What Moths Prefer- Moths prefer laying their eggs in corn before it tassels.  After the crop is in tassel, it will prefer neighbouring fields that are less advanced in crop stage OR they move to dry beans and other host crops (like snap beans, sweet corn etc).  Pick the tallest and healthiest looking fields that are not quite tasseling yet.

Where Eggs are Laid- Eggs are laid on the top 4 or so leaves, especially on those leaves that stand erect or just have or are about to unfurl from the whorl.  Eggs are usually on the upper (hairy) surface of the leaf.

What WBC Eggs Look Like – Egg masses can range in size from smaller than a dime to bigger than a quarter.  Each individual egg is shaped like a tiny cantelope.  Initially they are pearly white when first laid but turn tan and then purple just before hatch.  Click here to see a picture of how an egg mass changes colour as it ages over time.

How to Scout – Select the appropriate fields based on information above.  Inspect 20 plants in a row.  Inspect the upper leaves for both egg masses and young larvae.  If any are found, make note of the age of the egg and when it might hatch.  If young larvae are found, make note of their location on the plant.  After scouting those 20 plants, cut across the field and pick another 20 plants in a row.  Continue this until you have inspected 20 plants in 5 areas of the field.  That gives you a total of 100 plants inspected per field.   Eggs will be laid in patches in the field so you may or may not come across one of these hotspots during your scouting attempts.  Change up the areas of the field you monitor so that you are more likely to hit one of these hotspots in one of your scouting trips.

Threshold in Corn – If 5% of the plants (or 5 plants if you have scouted all 100 as suggested above) have egg masses on them, the corn needs to be sprayed.  Spray may not be required in those fields containing Cry1F (Herculex or SmartStax) as this type of Bt provides the crop with some protection (similar to one spray of insecticide).   However if populations are high, Cry1F fields may also experience damage.

Spray Timing – Time the spray application to immediately after the majority of the eggs have just hatched.  This will be one or two days after the eggs have turned purple.  This will ensure that you are targeting the smallest larvae which are the easiest to control.  These small larvae will be close to the top of the plant near the tassel unless there are already silks on the plant.  If silks are present, then the larvae will be attracted to the silks and may be hanging around the ear.  You must control the larvae before they enter the ear and are protected from the spray.

Chemical Control Options: Both Matador and Decis are registered on corn for western bean cutworm control.  See the 2010 supplement for Pub 812 that is now available at  http://www.omafra.gov.on.ca/english/crops/pub812/sup/p812suptoc.htm for label rates and recommendations.

Next Blog:  Update on this weeks moth catches, when peak moth flight is expected and dry bean management recommendations.

Lots more WBC moths have been captured in Ontario in the last couple of weeks.   We have been having some technical difficulties with our online trapping system and some participants are still not entering their trap data or site information.  But from the data that we have been able to collect, I can say with confidence that we have accumulated at least 364 moths, as of early last week.  To put this in perspective, this time last year we had only captured 4 moths in our traps.  Moths have been captured from Essex county all the way into southern Quebec.

To view all of our Ontario and Quebec maps to date, click here.  I also created a map with the data we are able to use to show WBC Trap Counts by County up to July 3rd.

Michigan and Ohio are also breaking records.  Michigan has accumulated at least 3771 moths and Ohio has captured 927 so far.  Speaking with my NY colleague today, they have now caught moths as far east as Long Island New York.

What does this all mean?

Moth flight continues to increase.  They are apt to still be attracted to corn to lay their eggs but will prefer those fields not in tassel yet.   Scouting for egg masses in corn fields is advised.  Dry beans in regions where most of the corn is already in tassel may also be at risk.

I will write a blog tomorrow and a CropPest article for this week to provide you with all information needed to scout and manage your corn and dry bean crops for western bean cutworm.