- Bryan Jensen's going to talk a little bit
on managing European corn borer
in the absence of traits.
Bryan currently works with UW-Extension
in the integrated pest management program
at the department of Entomology.
Please welcome Bryan Jensen.
(applause)
- Thanks, Larry.
When I was given the title to talk,
I thought this title worked great.
Then I realized there might be a small segment
of people in this audience that may not
know what ECB stands for.
I'm being a little facetious.
Certainly you've heard of it.
It's European corn borer,
but have you had the chance to scout for it?
Look for it? Manage it?
Some people could nod their head.
The older people in the room can,
but you look around the room,
there's a lot of very young people
and likely since a release of the above ground BT traits
that has really knocked corn borer populations back down,
and for the most part,
I'll bet a lot of the younger people,
younger than Dan,
have not had to deal with it.
So, that's the reason why they asked me
to talk about the European corn borer.
Why discuss it?
I give you one reason,
but another reason if you're here for Chris' talk.
This has been tied to the lowest population
of European corn borer in the 74 year history
of the DATCP Survey.
So, why talk about it?
We are getting locally heavy populations,
and why are we getting those?
Couple possibilities.
I don't think it's resistance,
in fact, I'm relatively sure it's not a resistance problem.
But I think in part, those areas will have
a lot of Non GMO host crops planted in the area,
so that will help support the populations a little bit.
And also, there may be some other native non-crop
host plants planted as well,
but also, I think one of the other driving factors
might be that we're seeing more conventional
corn being planted and that too will help
support corn borer populations.
But again, there's no reason for me to think that
these locally high populations are result of resistance.
The topics I'll cover:
Identification, life cycle, damage symptoms,
scouting, economic thresholds, and management
for European corn borer.
Little introduction,
European corn borer, Ostrinia nubilalis,
for what it's worth, that's the Latin name.
Their in the family pyralidae,
which is kind of unusual for our field crop insect pest.
Most of our Lep. pests are noctuids.
It's an introduced pest,
I think Krista had mentioned that.
Roughly, early 1900's when it was first introduced.
Probably came from Italy/Hungary on broom corn.
And broom corn is just what it is.
It was a type of corn plant
that was imported to make brooms.
Official detections:
Boston was 1917 around the Lake Erie area,
they found it by 1921.
And then 17 years later, 1938 it was found in Wisconsin.
That's a relatively short period of time
when you think of the type of economy
we had back at the turn of the last century.
And then it moved onto Nebraska by 1944.
Right now European corn borer is found throughout
the continental United States and Canada.
The adults.
Typically, we don't talk about identification of
adult moth pests,
but for European corn borer,
I think we should take a little bit of time
to recognize what the adults are
because we can scout for the adults.
And when the adults are active and present,
that can give us the information that we need
to determine when to start scouting for
European corn borer.
The males and females look different.
The female is on the left.
They both have the same patterns on the forewings,
it's just that the male has more distinctive
or more contrast in those patterns.
And the male the abdomen tends to extend
past the forewing.
The eggs, gotta learn how to scout for them,
during second generation, that is what we look for.
When they're first laid,
they're a very creamy, white color
and they're laid one on top of the other,
a lot like fish scales.
On the picture on the left,
that's what we call the black head stage.
And that black head is the black head
of the developing larvae.
When you start to pick up that black head stage,
those eggs will usually hatch
within a 24-hour period of time.
The larvae.
We also scout for them as well as their damage.
When they first hatch,
they may be one or two millimeter in length.
They will have that jet black head.
The more mature larva
that you see on the right-hand side,
they tend to take on, not always,
but they tend to take on a little more
coloration in their body,
maybe more of a smoke grey color
or a tan-ish color.
And you can pick up some dots on the back,
but no real good way to identify them,
but based on the time of the year,
the crop they're in and that sort of thing.
And they will have that jet black head.
The host range for corn borer is pretty wide.
A lot of native plants that they can survive on,
but in terms of crop plants,
field, sweet, pop corn are good hosts.
Potatoes, certain varieties of potatoes
are very attractive to the adults to come in and lay eggs.
Snap beans and other succulent beans,
like kidneys and lima beans can be fed on.
Peppers and also on hops,
and that's just a sampling of the crop plants
that corn borers can use as hosts.
Life cycle.
There are five larval instars per generation.
The first generation peak moth flight
will be at roughly about 600 degree days.
The second generation moth flight is between
1550 degree days and 2100.
And the take home message there I think for that,
is that's about a three week flight period.
When you get an insect with multiple generations...
usually that first generation
is pretty short and succinct.
With each generation after that
it tends to get a little bit more drawn out,
and that certainly is the case with
European corn borer.
So, that's about a 3 week flight period,
and that will make managing,
economic management of a corn borer,
in corn a bit more difficult,
because it will be very hard
to make one small-time application to control corn borer.
There can be, in some summers,
a partial third generation,
but that's a dead end for them.
If they do not make it,
and most of the time that
partial third generation will not,
they don't make it to the fifth instar, they will die.
They cannot overwinter.
They overwinter as fifth instar,
that is what you'll find inside the corn stalk right now.
And they'll pupate probably mid to late May sometime.
Okay, we talked about moth identification
and why that's important.
Because we can use several monitoring methods
of the adults to better time
our field scouting activities.
Degree days is one of those,
we just talked about degree days.
You have a couple sources of information:
one is the Wisconsin pest survey bulletin,
do a search for Wisconsin and pest bulletin,
and that will be your number one choice
at the top of the list.
If you don't get it, I will ask, "why not?"
It is an excellent first alert bulletin.
Whether you get it for degree days or not,
get it, please.
Your other source of degree days
is the UW-Extension Ag Weather website,
that's a URL for it, and I think if you did a search
for UW-Extension Ag weather,
that too will be the top choice.
That will also give you degree days
in near-realtime.
At best it will be one day old,
but you can also get degree days for seed corn maggot,
stalk borer, hop vine borer, and alfalfa weevil.
DATCP will also publish their black light trap results.
That can be an excellent way to monitor for adults.
That's something you're not gonna do yourself.
Black light traps are expensive,
they're difficult to go through,
they're not a lot of fun,
I don't like doing it,
but you can get that information from
the pest survey bulletin.
And again, that's gonna help you time
your field scouting activities.
If you look in some of the catalogues,
you will see that pheromone traps
are available for European corn borer.
I caution against using them.
In general, pheromone traps are really good
because they attract one species.
But there are some problems with corn borer
and that main problem is
that there are two strains present in Wisconsin.
There's an eastern strain,
which is a bit more common
in the eastern part of the United States
that tends to feed on non-corn hosts,
but it will also feed on corn.
And there's also the Z-strain,
which is the predominate strain in the Midwest,
it does have a greater attraction to corn.
But we have both strains in Wisconsin,
and I'm not sure if you do plan on doing that,
you'll need to use a couple pheromone traps.
One with the E-strain and one with the Z-strain.
The other thing that you could easily use
when monitoring for adults,
is go to their action sites.
These are usually found around field edges,
grass waterways, ditch banks, terraces,
things like that.
The grass species that they tend to like the best
are the bromes, giant foxtail,
and there's other grasses.
Grasses that tend to collect a lot of dew in the morning.
Because that free water is really important
to the adults.
If they get stressed from lack of water,
they tend to lay fewer eggs.
And their aggregation sites,
those are areas where the adults tend to aggregate.
In part to get to free water and because they're aggregating,
that's where they tend to do adult-like things.
Like mating and then moving into the field
to lay eggs.
So, again, to leave you with the final bullet on there.
By walking those action sites,
that will again help you time
when your field scouting activities should be starting.
Okay, let's talk a little bit about first generation damage.
And I should have put that in quotes.
First generation damage...
The damage you get on the corn
is not dependent on the generation,
but rather on the crop stage.
Usually with the first generation
we're talking about vegetative corn.
Although, if we have second generation
on very, very late planted field corn,
or even sweet corn,
you could have first generation type damage.
The first couple of instars,
again very small, will be more leaf feeding,
and that's not considered economic at that point in time.
And your symptoms will be shot-holing,
maybe a window paning,
and eventually as larvae get bigger,
you can get transverse holes across a leaf.
How does that happen?
When they first hatch,
they migrate right down into the whorl,
again we're talking about vegetative stage corn,
and initially, they will start feeding
on those rolled up corn leaves.
And I have a picture of the damage
in just a little bit you can see what we mean by shot-holing.
It looks like you stood back about 30 yards,
shot the plant with a shotgun,
and there's random holes throughout
the newly emerging leaves.
Again, that's not economic,
but it's a sign of things to come.
The other type of damage that first generation can do,
is tunneling into the stalk.
That usually starts about with the third instar,
when they're about 3/8 of an inch long
or the size of a dime.
And their galleries,
their stalk tunneling,
will usually be at the ear zone or lower.
Sometimes that might help you,
as you're doing a postmortem.
Tell if you're have problems
with first generation or second
based on where that tunneling is found in the stalk.
It's not fool-proof, but it can help.
And for each larva
on first generation,
they can cause about 5 % yield loss.
There's a picture of the shot-holing I was talking about.
Take a close look, these holes are small,
and they're from the newly emerging leaves.
The other thing you can look at
is those newest leaves coming out of the whorl,
they have no damage.
What does that tell you?
They have burrowed into the corn stalk
and part of that message is
once they have burrowed into that corn stalk,
you cannot control them.
You have to control first generation
when they're feeding in the whorl.
Second generation damage.
We're gonna talk about usually reproductive stage corn.
The leaf or mid rib feeding
will be just the initial feeding after hatching.
That will be a very brief period of time.
When they start tunneling into the stalk,
typically I'd mention that will be
from the ear zone and above
as compared to first generation,
and the tunnel length from second generation
can be quite extensive.
If they're in the meat of the stalk just above the ear zone,
you might have a half inch, inch, inch and a half gallery.
If they're burrowing into the corn plant up by the tassel,
you might have a 5 inch or longer gallery.
And one of your symptoms of second generation damage
can be a broken tassel.
Stalk lodging,
and stalk lodging is a generic term
we use that covers just about anything
that makes the corn plant go over.
It does look significantly different from
root worms, from compaction,
but not all that different from some of the stalk rots,
and with corn borer, what we usually look at
it's more of a kinking of the stem
with that stem bent over at
a 45 degree angle or more.
With second generation,
we're looking at a physiological yield loss
of about 4 % per larva,
and then you have the harvest loss
and that I cannot put a damage estimate on.
That's from feeding on the ear shank.
They're hollowing out that ear shank.
The ear shank gets weak,
and then that ear drops to the ground.
There's also harvest loss
just from the fact that the stalks have lodged.
They break off when you try to combine them.
Then finally I talk about ear shank damage.
They can do some direct damage to the ear
by feeding on the kernel.
That, in field corn, is generally minimal.
A few kernels, that sort of thing,
usually not considered too economic,
unlike it would be with sweet corn or pop corn.
But it can be a potential entry point for ear rots.
Okay, that's a second generation entry hole
for corn borers.
You can see a little frass showing up
on the outside of this stalk.
A gallery on the left,
a smaller one on the left.
The one on the right is relatively fresh,
you can still see the larva in there,
but once that larva is finished up
or been killed by predators,
you tend to get a browning of the stalk.
Some of the ear drop,
we just talked about that a little bit.
That's in addition to that
4 % physiological yield loss.
And here's a picture from the 1950's probably,
and don't think that anything from the 1950's
is considered old,
but I wanted to show you this,
just give you an idea what we had to deal with
in the days gone by.
So, this was from the probably the mid-1950's,
but during the mid-1990's,
we were dealing with populations
almost as high as what you see in this classic photo.
During that period of time
we had significant lodging by corn borers,
and that's about the time that the BT hybrids
became on the market.
Okay.
Scouting for first generation.
Our scouting procedures are different
for first generation as it would be for second.
On first generation scouting,
start at about V6 or later.
You don't need to scout much earlier than that,
because there's a
feeding deterrent called DIMBOA
in very young corn.
That if corn borers hatch and they do start to feed,
they'll quit feeding and they'll die.
Once you get to the V6 stage of corn or later,
that concentration of DIMBOA,
that's an acronym for a long name
that I can't begin to pronounce,
that concentration lowers
and corn borers can survive in V6 or later corn.
Procedure would be to examine
five sets of 20 plants per field,
100 plants total,
and look for that shot-holing.
Determine what percent of the plants are infested,
and then it's also important,
in two damaged plants per set,
pull out those whorl leaves.
Unfurl the corn leaves and count the larvae.
And the reason for that is,
remember when we were talking earlier about it,
the damage?
Each larva will cause about a 5 % yield loss.
And one more point on that,
if we're finding a lot of first,
maybe early second instar larvae when we're scouting,
you might have seven or eight, nine larvae per whorl.
Don't count those. Come back later.
There can be very, very high mortality
of first/second instar larvae in whorl stage corn.
Especially if it's been hot and dry
or you get a good, hard driving rain.
The economic threshold for first generation corn borers.
Kind of a worksheet-type program.
The first three lines were taking field information.
Percent of the plants infested.
The average number of borers per plant to get an average,
to get a field average.
Then we take that field average
of number of corn borers per plant
times the 5 % yield loss,
and what we're trying to do is look at how much
yield loss we're gonna have
in that one particular field.
And then you can read through the rest of the lines
if you want to, but then you try to put
a dollar estimate on that loss
and then you compare it
with what your control cost might be.
Keeping in mind, if you look at line number five,
we do not control 100 % of the larvae.
We do not control 100 % of the insects.
Our best guess for percent control
with European corn borer first generation
is 80 % control.
That worksheet is in A3646, the Extension publication
Best Management in Field Crops
and you can go to Extension's website,
search for the learning store
and you'll get a whole host of Extension publications
and then you can do a search for that.
Second generation, typically,
when things work out just fine,
it's the timing when they're laying eggs
will be usually late,
late July,
early August,
first two/three weeks of August,
that's usually post initiation of the tassel.
We talked about the flight period
1550 degree days, that's base 50,
to 2100 degrees.
Examine ten sets of five consecutive plants
and count the number of egg masses on that plant.
Egg masses will be laid usually,
90 %,
within the ear zone, by a leaf or two.
They can be laid on the top of the leaf,
on the bottom of the leaf, usually close to the mid-rib,
although not always.
If you find them on the top of the leaf, count them.
If you find them on the bottom of the leaf, count them.
If you find them on the flag leaves or the husks
or on the husk itself, count them.
If you find them on the stalk, count them.
But I would not spend a lot of time reviewing,
looking at the whole stalk,
that's maybe a one in a thousand type situation
where they will lay eggs on the stalk,
so for the most part,
just look at them on the leaves
and keep track of the number that you find.
For second generation we have a similar worksheet.
It works out pretty much the same as it did
for the first generation.
And the value of these
is you're not using a single economic threshold
that's been developed.
Here you can develop one for yourself
for that field
with that yield potential,
with that expected selling point
and you can really fine tune
what that economic threshold is.
As far as rescue treatments,
we're probably getting close to running out of time,
and more importantly lunch,
but we have several insecticide classes
that are available.
Probably the top one are the synthetic pyrethroids
in terms of the number of labeled insecticides.
The diamides, the chlorantraniliprole,
flubendiamide are also good insecticides to use.
If you're an organic situation
and want to use an organic BT product,
timing is gonna be really critical.
For the BTs to work the best,
you have to have really, really small larvae,
first or second instars.
We do have some organophosphates
that are labeled for use on corn.
There are still some carbamates,
but one of two problems with them,
they are either very short residual
or they're very toxic.
And as a result there's better choices.
A lot of natural control
going out there for European corn borer.
We have the predators that can feed
on both the egg and larvae.
Things like lady beetles,
a number of species available.
Minute pirate bugs, there are parasitoids,
and by that I mean,
it's an insect that's feeding on another insect
and it spends a majority of its time
feeding on a single host.
We have the trichogramma species
that can feed on the eggs
and a number of parasitic wasps and flies
that can feed on larvae.
When conditions are right,
we have several pathogens
that can control both the adults and the larvae.
There's a fungal pathogen, beauveria.
There's BT, that can kill only the larvae.
Then also microsporidia called nosema.
Different species of nosema can affect different adults,
and it may not kill them,
but it will reduce the number of eggs that are laid.
Finally, birds can be quite a predator
on larvae.
You can walk into a field which has
significant number of larvae feeding on the ears
and the husks are stripped from birds feeding.
They have found that and used it as a food source.
Then finally, Cultural Control.
I'll end with this slide.
Yes, stalk chopping can help control
European corn borer populations,
but it's most useful on a landscape level.
If you do it only in your fields,
the adults are migratory
and they can move around
from one field to the next.
So, there might be limited value to stalk chopping.
But what you can use,
even if you were not able to treat
for European corn borer,
use that field data to plan your harvest schedule.
On those fields that have
the highest corn borer populations,
those'd be the first ones that I would wanna harvest.
Maybe even a silage corn,
if at all possible.
But if grain is your only choice to limit
stalk lodging or ear dropping,
those'd be the fields that I would harvest first.
Any questions?
(applause)