Is corn rootworm getting your corn down?

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I'm Ryan Miller, Crops
Extension Educator.

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All right. Good morning
and welcome everybody.

I'd like to welcome you today to

our Strategic Farming
Field Notes session.

These sessions are
brought to you by

University of Minnesota
Extension and also support

from the Minnesota Soybean
Research and Promotion Council

and the Minnesota Corn Research
and Promotion Council.

We'd like to welcome you
today to our session

on corn worm getting
your corn down.

I'm list I'm a regional
extension educator

and crops out of

the Worthington Regional
Extension Office.

I'll be moderating today.

We welcome Bruce Potter.

He's our IPM Specialist out of

the Southwest Research and
Outreach Center by Lambert,

and also Dr. Fay,

he's our new extension
corn entomologist.

We're happy to have him
on board as well too,

and learn more about what he's
doing and seeing as well.

Anyway, with that, we'll
just jump right in.

We did get some questions
earlier on with

the registration that do
relate to our topic today.

Again, we're going to
focus on corn worm,

but we'll hit other pests
if we have some time.

But basically just take

a step back before we dive
really into the details.

Could you just explain, maybe

we'll start with Bruce
here just talking

about what's

the corn worms life cycle
through the stages,

what are things that
we got to worry about,

When can we actually control
these pests and so forth.

But again, just give us

a little basics so we're
all on the same page here.

Well, sure to start with,

at this time of year, basically,

for the most part all your
rootworm management is get

directed towards the
following corn crops.

Right now the beetles are
mating, are laying eggs.

Rather those eggs will diapause,

they have to rest
over the winter.

They'll hatch in the
spring. The larvae hatch

usually the beginning of June,

1 week of June or so in
this part of the world.

They'll feed for a few weeks,

they'll pupate and
then the beetles

will start coming out in,

in mid to late July.

Beetle emergence is
still happening,

so it's not like all
the Beatles eggs

hatch at the same time and

beetles emerge at the same time.

It's a long extended period
that ties into scouting.

And the other thing
that varies between,

we've got two species we're
dealing with in Minnesota,

Northern corn rootworm
and Western Cort worm.

The difference between
the two species is that

northern corn rootworm have

evolved a way to get
around a crop rotation.

And they simply do that by

delaying part of
that population,

delaying egg hatch
or another winter,

sometimes 34 winners.

And that'll put them
back into either you get

around environmental
stress that way or you

can get around pretty short
corn soy bean rotation

with that egg catch strategy.

Okay, good. Yeah,
thanks for that.

And then of course, people

wonder what are key ways
to control corn rote worm.

And I don't know if
you want to take that,

maybe just think about what are

some traditional methods people

use to control or what
have we been doing.

But where are we seeing the
holes with this as well?

Yeah, I think right now,

strategy used for
management of cong worm,

it depends on I
think the first one,

like you can use crop rotation,

that's the best strategy and

the cheapest strategy
to manage con,

rootworm like a con,
solving rotation.

And the second you can use
likes liquid granular.

I think in low project

probably liquid insects can
works a little bit better.

But then in high project
granular insects will be better.

Another important way
to manage traits.

Now most of the
Western and northern

cong worm have developed

resistance to some of

the BT traits. That's
a major concern.

I think the industry
is developing

some new BT traits
in the near future.

Should have allowed. Bruce, do

you have anything to add on?

The good news is that
it's not good news,

but western corn
rootworm rootworm trade

started in about 2005.

By 2009, we started to see

resistant western corn root
worms in southern Minnesota.

That's pretty short duration

for that trait to be
completely effective.

I think it speaks to that.

Those worm population genetics
are really pretty diverse.

They've got a lot of ways
to get around resistance.

I talked about the Northern
and crop rotation resistance,

Westerns and BT
resistance in Nebraska.

They've got some per
thid resistant beetles

now, rot worms.

Now I think the good news
is out of this whole thing

is that for the most part
we're getting reports

of extended diapause or northern
corn rootworm pressure.

For the most part, the
BT's seem to be working,

but there has been resistance
documented in North Dakota.

We've had seen some resistant
populations in Minnesota.

And I think that's
what we're really

trying to keep our
eye on right now

is our northern getting

around the BT's as
well as the Westerns.

Yeah, that's okay. Go ahead.

Okay. Yeah, have something to

add low populations
for Condor think

it's if it's not
necessary to use

BT traits just avoid in this way

we can help delay reducts

and protect the technology
for the future.

That brings up a question too.

It's like why do we
see these shifting?

Do you think with
western corners,

it seems like for a while that

those populations
were a lot higher,

but now you're
saying we're seeing

more extended diapause,

typically is with the
northern corn rootworm.

Right. What's driving
these shifts in what

we're seeing out in
the field like it

seems are the populations
the northern corn rootworm,

are they going up now relating
to these issues more?

No, I think that's
exactly right.

The extended diapause trait
has always been there.

But when those
northern populations

are low, you don't notice it.

When the northern
populations are higher,

it's not the whole population
that has the trait.

At least I don't know of any
cases where that's true.

Maybe as high as 50% or

around 50% will display the
extended diapause trait.

But if you don't have the
Northern populations out there,

you won't see the
extended diapause.

Now as these Northern have

been increasing over
the last few years,

we're starting to see the
extended diapause pop

up and we're seeing it
pop up in new areas.

But as far as the BT resistance,
insecticide resistance,

those things, the root worms

are basically responding to
what we're doing to them.

They're adapting to our
management strategies.

That's why we need to use a
lot of tools and be flexible.

Like Fay mentioned, if

you don't have a
problem, leave it alone.

Well, that's a good
point because again,

I know a lot of
people haven't just

planting BT hybrids,
for example,

to manage corn rootworm,

but then some people have
been layering insecticides.

Are we still seeing
lodging in these fields?

Is that what you're saying?

We're seeing some of that
pop up as well and should be

using an insecticide planting
when we plant a BT hybrid.

No matter what to manage this,

I don't know who wants to
tackle that question first.

But again, management is
always the key question

of what we can do to
manage this pest.

I'll try to tackle it first.

You can chime in
at the end here.

But the problems for both
northerns and westerns,

I think those
populations tend to

increase in continuous
corn extended diapause.

Northerns are not westerns.

We don't have the root worms

they do in the eastern
corn belt that have

lost their affinity
to lay eggs and corn.

So they'll lay eggs and soybeans

and they get around
to rotation that way.

As far as rotation resistant
root worms in Minnesota,

as far as we know, it's
only the Northern.

But those continuous corn fields

are ideal environments
for both species.

The populations build up

resistance develops in
those fields as well.

We do have some of

these really high
western corn rootworm

population fields that have

adapted to BT or
resistant to BT.

You do need a insecticide
to help keep things going.

Some of these fields
are bad enough

that really the smart thing to

do is to rotate out
of corn for a year.

It gets a little trickier with

the Northern and
extended diapause.

You've got to be aware
of what's going on,

but definitely rotating out

of corn for a year
is going to knock

those Westerns back and reset
the clock in those fields.

Yeah, that's correct.
According to some studies,

like if you do planting
continuous in the field,

if you have two species,

Western and Northern
Rum location,

normally Western rum dominate.

Be the dominant
species and they will

replace and has some
competitive biology.

The Northern um feel,

Western um should be
the dominant species.

And if you use car rotation,

you can kill them

almost one year and
the next year you

get back to con,
that will be better.

If a person has been doing

continuous corn or even there
haven't been rotated corn,

how would they get a feel for

their populations right
now out in the field?

What would you
recommend that people

do to see if they're
having an issue out there?

Obviously, scouting, but Okay.

What would that scouting entail?

That you would recommend
to be checking,

see if they have
an issue or not.

You're definitely
going to have to be in

the field to know if you've
got a problem or not.

And you're going to
definitely have to

get into the field,
not just on the edge,

if you're just scouting
the edge of a corn field,

that's where beetles
move in and out and

those populations tend to
be a lot higher there.

They might be high on
the first few rows,

and once you get
inside the fields,

populations may be low.

Scout the field thoroughly.

There's two ways,
basically you can do it.

One is to go into the field
and do whole plant counts.

Walk through the field,
you look at two plants,

you check for beetles in there.

Check around the ears and
then pull the silk spec.

There's a link in

the chat for some
information on scouting.

The whole concept is to
scout the field thoroughly.

You don't have to waste a lot of

time and whether you're doing

the whole plants
counts or you're

hanging sticky traps
out in the field.

It's getting the
field covered and

scouting long enough
in the season,

But if you walk into a field and

you've got Beatles
all over the place,

you really don't have to
spend a lot more time there.

You know, you're
going to have to do

some management of people

are using the yellow
sticky traps now.

But I'm going to
caution them because

the rootworm populations are

variable, even within a field.

And fa, and I, we're looking at

roots from some corn
rootworm studies yesterday.

Even from rep to rep,

that population
varied and that's

because the egg laying and

the beetles populations varied.

Even that small test area,
they're real variable.

Putting one or two traps in
the field is likely to give

you a completely wrong
impression of what's out there.

How many sticky traps do you

think they should
have out there?

Do you have any feel for that?

And realistically because
it takes time to do this,

how often you have to
check these and so forth?

Do you have a feel for how many

that person should put out
in a field if they were

going to put out sticky traps to

monitor for corn rootworm?

I can maybe answer that.

It depends on how much
detail you want out of that.

If you're just trying to
find high risk fields,

you can probably get by four.

Some people try three
that's getting iffy.

If you're on the bubble and
you're in that area where

you're not sure if you've got
a rootworm problem or not,

then you need six to eight.

And some studies Ken Oss
lab did a few years back,

the Northern's tend to need

a few more traps to accurately
assess the population,

but I think most guys are
just trying to figure

out which fields
are at higher risk.

You don't have to spend
too much time out there,

but you do have to do it for
a longer period of time.

And you're talking
about 34 weeks,

or because the Beatles
are either moving into

the field if they're
late pollinating

or later than other fields in

the area, those sorts of things.

Well, that's one
question too that brings

up what we're talking
about, sticky traps.

We do have a question
that popped up here too.

It's deals with
root pruning there.

Again, do you recommend

people about digging
roots and since it is

a drier year to do you think

there would be more
severe root pruning

or would it be less?

Or is it going to have
more of an impact?

Either. You want to tackle
that question there and

see what impact does

the dry conditions having
on root pruning this year?

Do you want to answer that?

I think you can ask it
because we dry condition.



I mean, if it's dry
out but you know,

because they're reducing
the root system,

that impact on yield is
going to be greater.

The other thing that
happens when it's dry

is especially if
it's hot and dry,

the roots don't
regenerate as well,

part of that's hybrid trait.

But the damage in

dry conditions or effect on

yield dry conditions
is usually worse.

But the other side
of that is that,

you know, if it's dry and
you don't have winds.

Um, you could have some pretty

severe damage and
it won't lodge.

The other thing I want to point

out is if you go into a field,

you don't know if
those beetles are

coming into the field
or leaving the field,

or if it's extended
diapause or not.

Unless you look at those roots

and see if there's a lot of
root injury in that field.

That's one of the issues
with rootworm beetles,

especially the northern's are so

darn mobile and they'll
move back and forth

between fields and even out

of fields and feed
on flower pollen and

that thing and weed pollen
on question also too.

That comes up a lot of times.

Now we're starting to see in
fields or volunteer corns

popping up through the
canopy and soybean fields.

What impact does that have on
corn rootworm populations?

To again, at what point is

it essentially that we're
not rotating out of corn?

Here again, we know

that rotation can help
overall with corn rootworm.

But again, if we've
got a lot of volunteer

corn out there point,

it's really not going
to help us, right?

Well, we did some work

a few years back and looked
at both Northern and western.

And it doesn't really take

that much volunteer
corn relatively

to pull beetles into
the field to lay eggs.

I think if I remember
the numbers right,

it's only like 2,500
plants per acre

or or you could have egg
laying in that field.

And that's not hard to do,

especially when we
have things like

those wind events that came
through a couple years ago,

lodged a lot of corn

and we had a lot of
volunteer corn following it.

I don't think
they're smart enough

to think of this
all on their own.

But from the rootworm side,

if you do have a lot of lodging,

you have a hard time picking
up some of that corn,

and that creates more
volunteer corn issues as well.

Volunteer corn is not good.

If it's out there till July,

you've got larval surviving.

And if it's out
there pollinating

later than everything else
towards the end of the year,

then you get a, you get

beetles moving in
and laying eggs.

Here's a question that I
did come in there too.

Have you noticed
any plant or cover

crops which promote
predators of corn rootworm?

Have either of you noticed
anything about that?

Is there any impact the
having more cover crops out

there might have on

on populations of corn,
rootworm and pressure?

I don't know if it's

the I mean the root worms

don't really have
that many predators.

There's some nematodes
that sort of thing.

But what do you think about,

you know, if you've got
a cover crop out there,

keeping that soil,
minimizing bare soil.

I don't know if that would
help on egg laying or not,

but I don't think I

have seen anything
published about it.

Yeah, I simply has
no study about lack

the prep the crop on
cidal management.

I think the impact of the
cover crop is going to

be what that does to corn
growth and root development.

Those moisture, those things,

Yeah, provide nutrition
for the corn development.

Related to that
question that we did

come in earlier as well.

They ask about beetle bombing,

probably not your favorite,

but if they do it,
what's the best timing?

Because if they see a field,

for example, with a lot
of beetles out there,

a lot of people
panic and want to

spray beetles because
they think they're

clipping their silks
and the corn won't.

Pollinate. That's
actually pretty rare.

After that corn is pollinated,

you can pull the Usse
back and shake the ears,

and if the silks swall off of

those kernels, they've
been pollinated.

But a lot of

that silk clipping actually

happens after the
pollination is all done.

That's a whole separate reason

for putting a foliar
insecticide on for adults.

And for the most
part, it's actually

pretty where you have

those levels of 5678
beetles per plant.

Then your corn isn't pollinated
yet and your silks are

clipped within to
the tip of the ear.

Some guys can't rotate
or won't rotate,

and they don't really have

a good way to put insecticide
on a lot of guys that

have tried to resort
to beetle bombing or

spring the adults to
prevent egg laying.

The threshold is one
beetle per plant,

but a lot of guys are
doing it too early.

This control would go

on after the silk clipping
and pollination is done.

For the most part, you're

talking about one
beetle per plant.

You want about 10% of
those beetles to be.

Females to be pregnant.

So you can see the swollen
abdomen swollen with eggs.

And you're probably
going to have to scout,

scout every ten days or so for

a while because like
I said earlier,

those beetles don't all emerge

at the same time and they
move in and out of field.

And your insecticide
residuals only so long,

one beetle per plant,

10% ravage females, and

then check the field
in seven to ten days.

And keep doing that.

Then you might have to put

another foliar application
on. Usually that's the case.

Here's, here's one more
question that came

in earlier with
registration as well too.

So you talked about a
lot of management again,

how do we best
prevent resistance

and maintain the
effectiveness of

the BT trades overall guidance

there that you would offer?

Yeah, I think as I
mentioned before,

using trades as necessary if

it's your project is
low in your field,

it's not necessary
to using trades.

First, you can avoid
a resistance problem

in the future and the second,

it will save you a lot of money

for buying those BT traits.

The second thing, if you
see any problem earlier,

you can use other insecticides,

different traits,
different mechanisms to

avoid insect developed resistance
to one model of action.

If you use multiple model of

actions that can slow
insect resistance.

Also I think right now
because of the problems,

especially for Western condom,

they have resistance to

almost every BT traits in

most of the locations
in the future.

I hope the industry
can have some,

we can have some new
model of actions.

One they're using right
now is NI plus BT.

And that can, your insect
project is low in the field,

but if your insect
project is high,

because I is working
totally different,

competitive BT, they
kill insects very slow.

It takes a little bit of
time, normally for BT.

They can kill the
insects one or two days,

but I takes about

like more than five days
to kill the insects.

That relates straight
to a question

that just came into it says,

what are you seeing
hearing about

the new traits efficacy?

I'm assuming that
they're talking

about the RNAI technology.

If you want to share
a little bit about

if people aren't that
familiar with how that works.

And again, what's the efficacy

of that you're seeing compared
to say, the BT traits?

Well, it's another mode

of action and it's a
supplement to the BT.

But as Fay mentioned, that
BT has to be functioning to

a certain extent because if
the insects are resistant,

the larva are resistant to
BT, they're able to feed.

They could do quite a bit of
root damage before the RNI

can kill, kill a larva.

I have seen some fields
this summer where they put

the RN hybrids under

extremely high rootworm
pressure and there's

problems log a lot of
root feeding and lodging.

I think the seed companies

will tell you too
that if you've got

really high pressure it's not
going to answer everything,

but it will help under

moderate and lower pressure

where you're dealing
with BT resistance.

It's a good tool but
it's not bulletproof,

just like any of
the other tools.

I'll just reemphasize that

if you want to help
root worms out,

you just keep doing
the same thing

over and over again
in the field.

And they'll figure a way
around it pretty quickly.

And here's another question.

Is there any non BT resistance
or tolerance out there?

There's differences in hybrids
and that sort of thing.

But I think one thing
that growers should,

can look at, the root system
of those hybrids themselves.

Something that's got a larger

root system maybe regenerates.

That'll help you
out if you're in

these high pressure situations

or worried about root worms.

That's something I'd always

look at right in the beginning,

is don't pick a small T hybrid.

It's just making your
life more difficult.

Here's one more
question that popped

up saying if you
mentioned already,

but northern corn rootworm

being found in new
areas of the state,

are there any
particular region and

counties that appears
to be heading

into versus where they're
regularly prevalent?

Where are you seeing the issues?

I guess they issues.

It's real localized and there's
no reason to its spills.

Not repealed in an area either.

This problem has been
here in the early '80s,

disappeared as northern
populations declined.

It came back in the early 2000,

disappeared, now it's
coming back again.

There's pockets in south
central Minnesota and

that Martin County areas

one little bit up
into Brown County,

I've seen some fields in stream,

southwest Minnesota, but
it's not quite as big

a hot spot but they're
seeing up in Douglas County,

I think into Otter Tail,

some areas where they haven't

seen extended diapause before.

They've had Northern corn

rootworm pressure
up there before.

One thing I didn't
mention as you go

north because the eggs
are more coal tolerant,

you see more Northern
corn root worms.

But even in southern Minnesota,

at one time, the Northern
were the dominant species.

It's fairly recent since

the Westerns became more
widespread down here.

I should note that you both have

written a really
great article that's

available on the
Minnesota Crop News

if people want more
details on that.

That has been posted online,

was posted earlier this week.

There's a lot of great resources

on our extension crops website.

We will have those
links close to

this recording as
well or you can find

it on our strategic
farming website.

For anybody listening
to this recording,

I did want to ask
you a quick know

that you're also working
with European Corn Board.

Do you have any thoughts you

wanted to mention about
that as well too,

because we can't totally
forget about that test either.

Yeah, like European combo

has been a historic
insects here.

But because of using
the BD treats,

it works very fantastic
to targeting the species.

But right now, I think
two years ago in Canada,

they found some species

European combo
showing resistance to

or proteins in Ohio state.

They're working
on some research.

They found resistance in

Northeast US showing
some resistance

of European combo
to there proteins.

The high chance
European populations

will come back in Minnesota
and showing resistance.

That will cause a
big problem for us.

The only thing right
now we want to

understand and to do some
survey understandability of

these insects to the
current BT technologies

that will help us a
resistance management.

If you find any infestation

of the European
combo in your field,

please did I can go and collect

some populations and test

it against the
current BT traits.

That will help a lot
for future research.

All right. Excellent.
Thank you Bruce.

I know you got like
about 1 min here.

Anything you want
to add? About time,

year, sleeping,
aphid, spider mites.

We've got dry conditions.

Spider mites, we'll probably
revise older news article.

We're starting to get some calls

in these drier areas
on spider mites.

There has been some
treatment going

on for a few weeks
in little pockets.

We did get some rain
in central Minnesota,

and I think not so much rain,

but if we can get some cooler
temperatures and we can

get leaf moisture
even with heavy,

get that for a couple
of nights in a row,

Hopefully we can get some fungi

going to knock those
populations back.

But ads are going to be
moving around the country

here pretty quick as soybeans
quit growing vegetatively.

Both of those insects
or ones And insects,

both of those are
something to scout

for here in the next week or so.

All right, and
stay tuned because

that will be something
we certainly can

adjust here on our upcoming
field notes sessions

as that anything
progresses there.

And also, I'm sure
you'll have stuff out on

the Minnesota crop
news as well too.

But again, I'd like
to thank our guests,

Dr. Feng and also
Bruce Potter today,

and all of you for attending

our extension field
notes session today.

And also, of course,
like to thank

the Minnesota Soybean Research

and Promotion Council and the

Minnesota Corn Research
and Promotion Council

for helping make these
sessions possible.

Have a great rest of the day,

and I hope to see you next week.

Is corn rootworm getting your corn down?
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