Stumpf Farm – Corn Rootworm Studies

University of Nebraska – Lincoln Author

08/31/2020 Added

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Dr. Julie Peterson presents results and recommendations for controlling corn rootworm larvae and beetles.
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[00:00:09.370]Hi, I'm Julie Peterson,
[00:00:11.240]associate professor and extension specialist in entomology
[00:00:14.770]at the West Central Research
[00:00:16.240]and Extension Center in North Platte.
[00:00:18.530]I'm pleased to share with you all
[00:00:20.090]some information that we have learned
[00:00:22.750]for Western corn rootworm management,
[00:00:25.050]based on several years
[00:00:26.610]of different trials and projects
[00:00:28.570]that we've done
[00:00:29.403]at the stumpf International Wheat Center
[00:00:31.620]and in some surrounding fields
[00:00:33.820]in that Grant in Ogallala area.
[00:00:36.230]Our most common species in Nebraska
[00:00:38.410]is the Western corn rootworm.
[00:00:40.580]This is a yellow beetle
[00:00:41.760]with black stripes.
[00:00:43.570]Adults emerge July through August,
[00:00:46.460]sometimes even later into September.
[00:00:48.940]They're gonna be mating and laying eggs
[00:00:50.690]in corn fields,
[00:00:52.110]and then spending the winter
[00:00:53.430]as eggs in the soil.
[00:00:55.490]They'll then hatch out
[00:00:56.490]as larvae next spring
[00:00:58.500]and this is when the larvae
[00:00:59.640]do most of their economic damage.
[00:01:01.900]They'll be feeding on corn roots
[00:01:04.190]and this can lead
[00:01:05.023]to physiological yield loss.
[00:01:07.130]Obviously, a corn plant
[00:01:08.290]that's been damaged by larval feeding
[00:01:10.430]can't take up water
[00:01:11.630]and nutrients as effectively,
[00:01:13.800]and then it can also result
[00:01:15.410]in goose snacking and lodging
[00:01:17.840]that makes harvest more difficult as well.
[00:01:22.540]Corn rootworm management
[00:01:23.900]in Nebraska usually involves
[00:01:26.250]the need to use
[00:01:27.083]more than one type of management approach
[00:01:29.627]and more than one management option.
[00:01:32.530]Some of those include crop rotation.
[00:01:34.780]This is by far
[00:01:35.920]the most effective management tool.
[00:01:38.900]The larvae really can only feed on corn roots
[00:01:42.230]and a few other species
[00:01:43.770]of closely related grassy weeds.
[00:01:46.420]So if you are rotating your crop to non-corn,
[00:01:49.890]and as long as you do a pretty good job
[00:01:51.630]of managing the volunteer corn in that crop,
[00:01:54.760]that can really just completely
[00:01:56.570]bring that rootworm population
[00:01:58.380]in the field
[00:01:59.310]all the way down to zero.
[00:02:01.219]That is a really a key part
[00:02:03.620]of a longterm management strategy
[00:02:05.670]to keep populations low.
[00:02:08.070]Aerial insecticide applications
[00:02:10.270]for adult beetles
[00:02:11.490]is also another tool,
[00:02:14.410]using Bt traits
[00:02:16.900]and using seed treatments,
[00:02:19.290]using at-plant insecticides
[00:02:21.200]that would target the larvae
[00:02:23.220]and then finally using biological control
[00:02:25.870]to supplement these other tools.
[00:02:28.160]And I'm gonna talk a little bit more
[00:02:29.690]about each of these options.
[00:02:33.280]So first, looking at aerial insecticides
[00:02:36.060]for adult control.
[00:02:37.610]This is really approaching it
[00:02:39.480]with two different goals in mind,
[00:02:42.220]depending on what you have going on
[00:02:44.210]in your field at the time.
[00:02:46.160]So the first would be
[00:02:47.520]the need to control adults right now
[00:02:50.070]within this season
[00:02:51.760]in order to prevent
[00:02:52.610]silk clipping from happening.
[00:02:54.910]Now, this occurs
[00:02:55.890]when you have really
[00:02:56.723]high beetle populations.
[00:02:58.930]So we're talking upwards of more than five
[00:03:02.010]up to 15 beetles per plant,
[00:03:04.860]so very large numbers.
[00:03:06.700]And they're also feeding on the silks
[00:03:09.110]and clipping those silks
[00:03:10.640]back to less than half an inch
[00:03:13.130]and this is when pollination
[00:03:14.930]is still 50% or less completed.
[00:03:19.210]So there's a window of time there
[00:03:21.100]where if you have
[00:03:21.940]very high beetle populations,
[00:03:24.000]you may need to spray
[00:03:25.200]to prevent silk clipping
[00:03:27.230]from being so bad
[00:03:28.430]that pollination is actually interfered with.
[00:03:31.900]Maybe a more common approach
[00:03:33.600]or a more often necessary approach
[00:03:36.750]for spraying for adult beetles
[00:03:39.120]is to prevent egg laying
[00:03:41.240]and you're actually not worrying
[00:03:42.950]about current beetles in the field,
[00:03:45.350]this season doing damage.
[00:03:47.350]What you're thinking about
[00:03:48.380]is the beetles
[00:03:49.213]that are there laying their eggs,
[00:03:51.140]and then those eggs will spend the winter
[00:03:53.580]and result in larval population
[00:03:55.860]the next year.
[00:03:57.140]So this other approach
[00:03:58.260]is thinking about management now
[00:04:00.370]that actually helps you
[00:04:01.390]down the line next year
[00:04:03.270]for managing beetle population.
[00:04:06.010]Choices insecticide product
[00:04:07.730]is gonna be really important
[00:04:09.130]whenever you're spraying
[00:04:10.060]for adult rootworm beetles
[00:04:11.930]and this is due to
[00:04:12.930]the numerous different times
[00:04:14.640]that rootworm beetles
[00:04:15.473]have evolved resistance
[00:04:17.040]to different products.
[00:04:18.820]Nebraska has a long history
[00:04:20.310]of this kind of resistance.
[00:04:22.250]The most recently documented
[00:04:24.580]is actually just in the last five years,
[00:04:26.680]we've shown that pyrethroids alone
[00:04:29.690]are really no longer adequate
[00:04:31.650]to control Western corn rootworm adults
[00:04:34.560]is where we first noticed it,
[00:04:36.410]but this actually does also translate
[00:04:38.870]over to larvae
[00:04:40.350]also showing pyrethroid resistance.
[00:04:43.120]And this is even documented
[00:04:44.630]in Southwest and West Central Nebraska.
[00:04:47.570]So some of our more common
[00:04:49.150]and some of our least expensive products
[00:04:51.840]that we have really relied on a lot
[00:04:54.270]things like Brigade and Capture
[00:04:57.380]Force would be another one,
[00:04:58.920]these are all in that pyrethroid grouping,
[00:05:01.670]and we are seeing concerns,
[00:05:03.790]we are seeing resistance
[00:05:05.710]to these products
[00:05:06.760]from Western corn rootworm
[00:05:08.380]and our part of the state.
[00:05:09.860]So I really wanna encourage you
[00:05:11.190]to move away from using those,
[00:05:13.550]especially using those by themselves
[00:05:16.100]and rotate in some other
[00:05:17.650]mode of action insecticides
[00:05:20.370]to try to move away from that resistance
[00:05:23.910]and try to move
[00:05:24.743]towards more effective products.
[00:05:27.250]So this is actually a figure
[00:05:29.240]that comes from some of that work
[00:05:30.970]that we did
[00:05:31.803]on the pyrethroid resistance,
[00:05:33.950]just to give you an idea
[00:05:35.150]of the sorts of issues
[00:05:36.200]that we were seeing.
[00:05:37.740]So what this is showing
[00:05:39.550]is the names of different populations
[00:05:43.072]of rootworms that have been collected from
[00:05:47.060]mostly from Nebraska,
[00:05:48.290]but from a few other states as well.
[00:05:50.610]Now, we expose these beetles
[00:05:52.970]to an amount of bifenthrin
[00:05:54.830]which is a very common
[00:05:56.150]active ingredient of Pyrethroid.
[00:05:58.430]We expose them to an amount
[00:06:00.010]that was supposed to kill 99% of them.
[00:06:04.130]Now, the populations here
[00:06:05.680]from Saunders County, Nebraska, Saline, Kansas,
[00:06:10.180]those are actually not different
[00:06:12.460]from the expected 99% dead.
[00:06:16.100]So those that are down the bottom in blue
[00:06:18.470]we're showing those beetle populations
[00:06:20.890]are still susceptible to the bifenthrin,
[00:06:23.840]the bifenthrin still works for them.
[00:06:26.280]But all the other populations
[00:06:28.180]that are up higher
[00:06:29.160]that's in sort of this reddish color,
[00:06:31.780]these are ones that actually died
[00:06:34.240]at a significantly lower amount,
[00:06:37.810]versus what was expected
[00:06:39.980]when they were
[00:06:41.100]had bifenthrin applied to them.
[00:06:44.050]So this would include
[00:06:45.010]multiple different populations
[00:06:46.630]these here on there from Keith County,
[00:06:48.880]Perkins County and Chase County,
[00:06:51.180]our Southwest part of the state of Nebraska,
[00:06:54.520]you can see there also were some
[00:06:56.190]from Northwest Kansas on there as well.
[00:07:00.450]But just to give you an idea that
[00:07:02.400]in some areas,
[00:07:03.730]in some fields in Southwest Nebraska,
[00:07:06.690]we expose the beetle
[00:07:08.570]to an amount of bifenthrin pyrethroid
[00:07:10.490]that was supposed to kill 99%
[00:07:13.710]and at very worst
[00:07:15.370]for a few of those
[00:07:16.370]Perkins County fields,
[00:07:18.530]it only killed 4% of the beetles.
[00:07:21.640]So definitely a significant resistance
[00:07:24.260]showing up there.
[00:07:25.610]And so this is the concern we have
[00:07:27.580]if folks are gonna be using
[00:07:29.050]pyrethroids by themselves,
[00:07:31.160]is that we don't want you
[00:07:32.140]to end up with this
[00:07:33.200]sort of a situation
[00:07:35.320]where you only have four or 5%
[00:07:38.160]of your beetles dying
[00:07:39.360]when you're expecting to see
[00:07:40.620]99% or more.
[00:07:43.720]Now, at the Grant research farm,
[00:07:46.210]our crew has done
[00:07:47.850]several years of Bt trait,
[00:07:50.680]seed treatment and at-plant insecticides testing.
[00:07:54.930]This is using small-plot trials
[00:07:57.320]mostly located at the Stumpf Farm itself,
[00:08:00.500]and we have been using
[00:08:02.070]this small-plot planter
[00:08:04.660]that's shown here.
[00:08:05.980]We have it set up
[00:08:06.890]where we can actually switch
[00:08:08.270]between different liquid
[00:08:09.620]and granular at-plant insecticides
[00:08:12.590]that are being put down in the furrow.
[00:08:15.000]We can also switch seeds,
[00:08:17.240]so we're able to test different seeds
[00:08:19.330]that have different Bt traits in them,
[00:08:21.250]or have different seed coatings
[00:08:23.570]or seed treatments on them,
[00:08:25.472]and this has really opened up our ability
[00:08:27.640]to test side by side,
[00:08:30.840]under heavy rootworm pressure
[00:08:33.140]at the Grant farm,
[00:08:34.660]how these different control methods
[00:08:36.850]and how these different products actually work.
[00:08:41.520]One of the main ways
[00:08:42.840]that we assess impact
[00:08:44.520]on corn rootworm populations
[00:08:46.930]and injury to the corn root system
[00:08:49.670]is by digging up plants
[00:08:51.350]and actually documenting
[00:08:52.660]the feeding injury.
[00:08:54.240]And we use a standardized scale
[00:08:56.410]from Iowa State University
[00:08:58.740]that rates from a zero to three,
[00:09:01.280]how much feeding damage
[00:09:02.770]to those nodal roots
[00:09:04.070]has been done by corn root worm larvae.
[00:09:10.250]Now there's a number of takeaway messages
[00:09:12.290]that we've gotten
[00:09:13.123]from doing these studies
[00:09:14.360]over the last several years also.
[00:09:17.010]One of those
[00:09:17.843]is to manage rootworm populations
[00:09:19.720]using crop rotation
[00:09:21.510]can really be great
[00:09:22.440]to keep the population low enough
[00:09:24.980]that really allows control methods
[00:09:27.140]to be the most effective.
[00:09:29.340]What we can see is that
[00:09:30.820]when larvae populations are really high,
[00:09:34.090]control methods can be overwhelmed,
[00:09:36.270]so even things that really
[00:09:37.500]are quite effective
[00:09:38.860]at low and medium infestation rates
[00:09:42.120]just can't make it over
[00:09:44.060]that threshold to very high population numbers.
[00:09:48.830]We also wanna avoid
[00:09:50.040]having the latest silking fields
[00:09:51.960]in your area.
[00:09:53.120]So this is actually a practice
[00:09:54.660]that we do on purpose to
[00:09:56.720]in order to attract in beetles
[00:09:59.300]because we'll have the latest
[00:10:00.590]silking fields in our area
[00:10:02.380]and then that sets us up
[00:10:03.470]to be able to have high populations
[00:10:05.190]to run our studies
[00:10:06.650]but this is something you obviously wanna avoid
[00:10:08.810]having happen in your fields if possible.
[00:10:12.760]We've also found
[00:10:13.700]that the Cry 34/35 protein
[00:10:16.550]is really the most effective Bt protein,
[00:10:19.270]but even that can be overwhelmed
[00:10:21.030]whenever those rootworms
[00:10:22.170]are at really high population densities.
[00:10:25.340]The Neonicotinoid seed treatments
[00:10:27.970]really can help protect the seed
[00:10:29.770]whenever you have low rootworm pressure
[00:10:32.155]but this really is only
[00:10:33.700]for early on in the season.
[00:10:36.560]And then not unlike what we talked about
[00:10:38.570]for the adults with the pyrethroids,
[00:10:41.250]we do find that for larvae as well,
[00:10:43.410]using a pyrethroid only
[00:10:45.630]is not going to be providing you
[00:10:47.663]with very much protection
[00:10:49.330]due to the resistance that's out there.
[00:10:51.830]So even though some of these
[00:10:53.040]liquified already products are inexpensive,
[00:10:55.920]they're easy to mix with your starter,
[00:10:57.890]if they're pyrethroid
[00:10:59.020]as the only active ingredient,
[00:11:01.390]they're not gonna be giving you
[00:11:02.810]a strong amount of protection
[00:11:04.470]against rootworm larvae.
[00:11:08.000]So the final thing
[00:11:08.890]I wanted to talk about
[00:11:10.040]was we've done some studies
[00:11:12.130]at Stumpf field
[00:11:12.963]and in some surrounding commercial fields
[00:11:15.180]and where we've actually identified
[00:11:16.720]some beneficial species of fungi
[00:11:19.520]and of nematodes.
[00:11:21.040]So that's what this picture
[00:11:22.320]is showing here
[00:11:23.153]is actually a corn rootworm larva
[00:11:25.690]that's been infested
[00:11:26.780]by this Metarhizium,
[00:11:28.090]which is a beneficial fungus,
[00:11:30.240]and it actually kills
[00:11:31.604]the rootworm larvae.
[00:11:33.200]So we're looking at ways
[00:11:34.130]that we might be able to introduce this
[00:11:35.930]as sort of a additional supplement
[00:11:39.090]that could work together
[00:11:40.270]and hopefully in synergy
[00:11:41.750]with things like Bt
[00:11:43.130]and with limited use of insecticides.
[00:11:46.600]A similar story
[00:11:47.690]for the entomopathogenic nematodes.
[00:11:50.090]These are nematodes
[00:11:51.090]that make their living
[00:11:52.090]by attacking and killing insects.
[00:11:54.490]They're not gonna be
[00:11:55.840]feeding on crop roots,
[00:11:57.590]they're not gonna be introducing
[00:11:58.820]any diseases to crops,
[00:12:00.550]really all they do
[00:12:01.390]is attack and kill insects.
[00:12:03.430]And so we're looking at ways
[00:12:04.760]to apply them
[00:12:05.760]and use these
[00:12:07.310]really as a biological control
[00:12:09.150]to help us combat this rootworm past.
[00:12:12.440]So really I think
[00:12:13.273]that kind of brings it back to
[00:12:14.890]my first point in all these
[00:12:16.180]which was that
[00:12:17.410]rootworm management is not a one
[00:12:19.370]or two silver bullets approach,
[00:12:21.730]you're gonna be looking at multiple
[00:12:23.090]different control strategies
[00:12:24.520]and how they can work together.
[00:12:27.100]So finally, I just wanted to say thank you
[00:12:29.580]and please feel free to contact me
[00:12:31.220]with any insect questions
[00:12:32.540]you might have,
[00:12:34.030]my email and phone
[00:12:35.880]and Twitter are all here,
[00:12:37.420]and thank you all very much.

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Stumpf Farm – Corn Rootworm Studies

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