Join the University of Minnesota Extension Crops team in addressing all your crop-related questions this growing season, from soil fertility, agronomics, pest management and more. We will tackle issues as they arise to help you make better crop management decisions this season.
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I'm Ryan Miller, Crops
Extension Educator.
Earlier this morning,
we recorded an episode
of the Strategic Farming
Field Notes program.
Strategic Farming Field Notes is
a weekly program addressing
current crop production topics.
A live webinar is
hosted at 08:00
A.M. on Wednesdays throughout
the cropping season.
During the live webinar,
participants can
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get questions answered.
An audio recording of
the live program is
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Thanks and remember to tune
in weekly for discussion
on current cropping and
crop management topics.
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.
Okay.
Yeah.
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.