3 - 2020 Soybean Management Field Days - Managing Insects in Cover Crop Systems
Managing Insects in Cover Crop Systems - Justin McMechan, University of Nebraska Crop Protection and Cropping Systems Specialist. This presentation includes: Risk and management of insects in cereal rye cover crop systems; Typically insect pests found in cover crop to soybean systems; and Overview of studies conducted on arthropods in cover crop to soybean system.
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[00:00:07.210]Hi I'm Justin McMechan
[00:00:08.043]I'm a Crop Protection and Cropping Systems Specialist.
[00:00:10.330]And although they can't join me today,
[00:00:11.980]Tom Hunt is also Research and Extension Entomologist
[00:00:14.580]in the Northeast, Bob Wright in Lincoln, Nebraska,
[00:00:17.810]but works at the South Central Ag Lab.
[00:00:20.310]And Elliot Knoell a Research Project Coordinator in my lab,
[00:00:22.980]and Elliot has helped a lot with the cover crop work
[00:00:26.040]that I'm about to discuss this year,
[00:00:27.360]he leads a lot of that effort.
[00:00:29.380]If you missed it, the previous video is soybean goldmine
[00:00:32.170]that's where you see what looks like a mosquito there,
[00:00:35.330]and some orange larvae.
[00:00:36.410]But now we're gonna move into what is cover crops.
[00:00:40.020]An area that's rapidly growing in the state
[00:00:42.140]and kind of an area that's hidden
[00:00:43.330]to cover crops are not typically discussed
[00:00:45.670]which is insect or largely arthropod management
[00:00:48.860]because we have a spider up there.
[00:00:50.870]And what do they mean in this system?
[00:00:52.300]Do we need to be concerned about them
[00:00:54.420]as we transition from cereal rye cover crop
[00:00:57.640]in this case into soybean
[00:01:00.380]and so we'll go over a bit of that.
[00:01:02.930]But prior to that I think we should kind of lay out
[00:01:04.820]a lot of the theory and understanding as to why
[00:01:06.750]a lot of people grow cover crops.
[00:01:08.260]There are soil benefits, soil health benefits,
[00:01:10.410]soil erosion reduction, a number of other possibilities,
[00:01:14.260]and my interaction with cover crops comes in the form of
[00:01:18.470]weed control which is paired up a lot with Chris Proctor.
[00:01:21.780]Which a typical response or what we would expect to see
[00:01:24.790]is as we increase the amount of cover crop that's present
[00:01:27.560]meaning the biomass is present prior to planting,
[00:01:30.660]we're likely to get some reduction
[00:01:32.820]in the weed presence or abundance in that field.
[00:01:35.750]And so this is a quick way
[00:01:37.450]of potentially adding other strategy
[00:01:41.240]to managing, you know, those problematic weeds
[00:01:43.890]that we're seeing in the system.
[00:01:45.970]If I overlay the same graph with a risk of pests,
[00:01:49.280]you see that I widened the bars dramatically
[00:01:51.250]from maybe a high degree of risk of pest pressure
[00:01:53.916]to very little or almost no risk of pests.
[00:01:56.930]And that's because it's largely unknown,
[00:01:59.210]how insects perform in this system.
[00:02:01.070]And they are highly variable year to year on what they do.
[00:02:05.560]And I could cross that out
[00:02:06.730]and I could replace that with beneficial insects.
[00:02:09.180]So these are insects that we wanna see in the system,
[00:02:11.720]they may manage early season pests
[00:02:14.347]that show up in the system.
[00:02:15.440]So growers need to be cautious.
[00:02:16.760]We don't wanna lob on an insecticide
[00:02:18.600]when we go to terminate our cover crops,
[00:02:20.560]'cause we may have a lot of good things in that system.
[00:02:22.830]Lots of factors to consider when we look at cover crops.
[00:02:25.490]Planting date of a cover crop in the fall,
[00:02:27.360]planting data to your cash crop in the spring,
[00:02:29.870]the species of cover crop that we might use,
[00:02:32.310]and the termination date when we plan on killing
[00:02:34.090]that cover crop relative to planting soybeans in this case,
[00:02:38.170]may influence arthropod communities that are present
[00:02:40.830]in that particular system.
[00:02:43.270]So we're not new to this
[00:02:44.470]lots of people have done research on this.
[00:02:46.820]You could see that there are a lot of beneficial outcomes
[00:02:48.940]that we've seen with predators in this system.
[00:02:51.200]Lots of these are from other states
[00:02:52.680]so you can see the map of the U.S. there.
[00:02:54.990]We have highlighted the number of studies in each state.
[00:02:57.950]We're down at one on arthropod studies in Nebraska
[00:03:01.160]and that was actually on corn
[00:03:02.720]which is one of the students in my lab
[00:03:04.040]when we had it pest outbreak a couple of years ago,
[00:03:07.020]we documented that.
[00:03:08.000]We have lots coming,
[00:03:08.833]so that's the good news especially studies like
[00:03:11.380]what we're about to discuss today.
[00:03:13.430]We get those predators as well as we get seed feeders.
[00:03:16.330]So we've been talking about managing weeds in the system.
[00:03:18.800]There are also a little crab beetles
[00:03:20.570]that like to feed on weeds seeds, so this is perfect.
[00:03:22.860]They take out weed seeds at weed seed bank
[00:03:25.930]so we really want to determine
[00:03:26.940]are those present in this system.
[00:03:28.970]But then unfortunately on the flip side of that,
[00:03:30.470]we have some pests that show up in the system
[00:03:32.100]and those have been documented in other states,
[00:03:34.360]as well as here on corn,
[00:03:35.950]we've not documented any major problems
[00:03:37.890]we'll discuss a few in soybeans,
[00:03:40.171]but nothing that's widespread and causing a major concern.
[00:03:43.850]But really in the risk of any pests in this system
[00:03:46.790]is based on their ecology.
[00:03:47.900]Are they attracted to cover crops?
[00:03:49.330]Are they likely to move into that system
[00:03:51.270]utilize it as a temporary source?
[00:03:52.930]Now when it disappears move to the cash crop
[00:03:55.620]that's where we typically see problems.
[00:03:57.830]So beneficial insects up in Minnesota
[00:03:59.660]they work with Soybean Aphid,
[00:04:00.760]that's a problem in the Northeast,
[00:04:02.480]can be we're not seeing as much this year.
[00:04:04.940]But predators that were transitioning off of cover crops,
[00:04:08.100]as you see in the image here to the right
[00:04:09.980]capitalized on Soybean Aphid
[00:04:11.990]really knocked down the numbers.
[00:04:13.960]Which was good
[00:04:14.870]because it probably eliminated
[00:04:16.390]some insecticide control measures
[00:04:18.360]that were needed in that population.
[00:04:19.540]So this is good news you could see
[00:04:21.420]they saw a lot of different things
[00:04:23.430]in that system from my new pirate bugs,
[00:04:26.120]which these are the ones that annoy you in your backyard
[00:04:28.050]and luckily there's none getting me now
[00:04:29.730]but they're the ones that poke you on occasion.
[00:04:31.870]Surfeit flies as well as lady beetles.
[00:04:34.350]So plenty of things documented that study.
[00:04:36.670]That study was mowed I doubt there's any growers
[00:04:39.820]or not many that are listening to this
[00:04:41.330]that mow their cover crops out,
[00:04:43.040]most use a herbicide like Roundup to
[00:04:47.650]remove those cover crops in preparation for planting.
[00:04:50.940]So a few pests to discuss in the system,
[00:04:52.680]these are things to watch out for.
[00:04:54.340]The best thing is that
[00:04:55.320]they have good degree day formulas for them
[00:04:57.170]so we know when they show up in the system.
[00:04:59.120]We saw pest pressure from seed corn maggot this year,
[00:05:02.010]in soybean fields.
[00:05:02.940]It wasn't necessarily associated with cover crops
[00:05:06.180]but this is one even with good seed treatments
[00:05:08.370]just environmental conditions can make those seed treatments
[00:05:11.280]less effective and sometimes we can have problems.
[00:05:14.030]So adults move during the spring,
[00:05:16.430]they're attracted to decaying material vegetation
[00:05:19.460]so growers that might tail in a cover crop
[00:05:21.680]which also isn't very common can be really attractive
[00:05:24.070]without decaying material.
[00:05:25.640]And you can see here we had damage in 2018
[00:05:27.880]as well as this year which I mentioned,
[00:05:29.690]with radishes where some survived
[00:05:32.110]and were tilled in the spring
[00:05:34.140]bringing in a lot of adults that laid eggs.
[00:05:37.750]And so you could see we have a degree day formula there,
[00:05:39.740]360 degree day units.
[00:05:41.670]We typically publish these each year
[00:05:43.700]and so you can monitor that for determining
[00:05:45.967]whether or not you are at risk
[00:05:48.930]of seed corn maggot entering your field.
[00:05:52.960]Black Cutworm's another one,
[00:05:54.080]this one doesn't over winter in the state,
[00:05:55.800]dingy cut worm and other cutworm does.
[00:05:57.680]We don't typically see problems from that one
[00:05:59.720]because it doesn't cut off plants,
[00:06:01.050]black cutworm can cut off plants.
[00:06:03.300]It is more of a problem in corn
[00:06:04.960]because our soybean populations can take big hits
[00:06:07.300]early in the season as long as they're sufficient
[00:06:09.840]they tend to pull through.
[00:06:11.540]This one's attracted to black cutworms
[00:06:13.350]is attracted to dense vegetation the spring as it moves up,
[00:06:16.520]we monitor for it with pheromone traps.
[00:06:18.600]And so when it comes in it lays eggs
[00:06:21.040]in that dense vegetation
[00:06:22.550]and begins its development on it,
[00:06:24.120]if it's killed off mid development
[00:06:25.730]it will likely move to whatever cash crop is present
[00:06:28.180]to complete its development
[00:06:29.240]which may mean injury for the field.
[00:06:31.890]There's a bit of diagnostic features
[00:06:33.320]you can find lots of these at the UNL entomology webpage,
[00:06:36.900]if you need more information on identifying the adults
[00:06:39.420]which we have pheromone traps for
[00:06:41.310]or the caterpillar itself.
[00:06:43.800]So we have this bio fix where we monitor for it,
[00:06:45.710]if we get eight or more over two nights
[00:06:47.300]we start this ticking time clock,
[00:06:49.650]it's the time clock on when to scout.
[00:06:52.170]And so you could see all that in the information there
[00:06:55.320]on the slide in terms of a table from the biofix
[00:06:58.380]to when we start seeing any feeding symptoms.
[00:07:00.130]It's good to scout early for something like this
[00:07:02.360]if you need to take any management.
[00:07:04.380]So let's get into the study that's behind me here,
[00:07:06.870]which has been conducted for a couple of years now,
[00:07:10.300]we did wheat early on in 2018,
[00:07:12.350]and then we focused solely on cereal rye
[00:07:14.170]for the last two years.
[00:07:15.760]We terminated these cover crops two weeks prior
[00:07:18.160]to planting soybeans at plant and five days later.
[00:07:20.930]So this really represents the range of when growers
[00:07:24.750]might be terminating a cover crop
[00:07:26.300]either based on NRCS guidelines
[00:07:29.060]or maybe their own inclinations on managing cover crops.
[00:07:32.920]And so we looked at biomass at termination,
[00:07:34.590]how much biomass of a cover crop was present.
[00:07:36.650]what the extended leaf height was.
[00:07:38.630]Those are measures to the benefits
[00:07:40.870]that we might see from cover crops,
[00:07:42.550]in terms of erosion or other benefits mentioned earlier.
[00:07:46.090]And then from the insect standpoint,
[00:07:47.810]we looked at damage assessments,
[00:07:49.710]how much feeding was present,
[00:07:51.600]the number of plants that were impacted,
[00:07:53.470]as well as the severity.
[00:07:54.530]How much were they feeding on those plants?
[00:07:57.070]Is any management necessary?
[00:07:58.420]Does that vary by practice?
[00:08:00.220]And then we also looked at what's called a pitfall trap
[00:08:02.630]which is basically a hole in the ground
[00:08:04.520]where we can place a little bucket
[00:08:08.090]and insect crawling across the sole surface
[00:08:10.050]fall into that trap,
[00:08:12.470]and then we can count the numbers that are in there.
[00:08:14.700]Lots of soil dwelling insects get captured in that
[00:08:16.760]there's a lot of beneficial insects
[00:08:18.560]that get into those pitfall traps.
[00:08:21.830]So you could see we've covered a lot of locations
[00:08:23.770]courtesy of soybean management field days
[00:08:25.530]as well as the research stations.
[00:08:27.920]And this year we had to limit our activities due to COVID
[00:08:30.580]so we were only a three locations,
[00:08:32.370]when in the past we've been as high as seven locations.
[00:08:35.460]And so today I'm gonna focus on the 2020 locations,
[00:08:38.460]you're welcome to look into the books of previous years
[00:08:40.780]where we have a lot of information
[00:08:42.560]on what was captured in those previous years.
[00:08:45.100]So refer to your book on the area for entomology
[00:08:48.660]to look at more information
[00:08:50.320]on what we found for specific details
[00:08:52.920]cause I'll be briefly covering kind of a highlights
[00:08:55.150]of this this year.
[00:08:57.480]So here we have two graphs presented
[00:09:00.470]on the bottom is the locations,
[00:09:01.990]as well as the treatments for termination
[00:09:04.110]you can find the dates of those terminations in the book.
[00:09:06.930]But then on the Y axis of each one of those,
[00:09:08.950]we have the cereal rye height in inches,
[00:09:12.110]as well as the biomass
[00:09:13.470]and you could see that we were roughly
[00:09:15.360]between six and 10 inches when we first terminated
[00:09:17.680]and got as high as 22 inches on our last termination.
[00:09:20.580]So delaying those terminations up to
[00:09:22.880]and past planting soybeans
[00:09:24.800]really led to a lot of additional growth.
[00:09:28.190]The height is nice but the biomass is the biggest indicator,
[00:09:31.040]it's the hardest thing to take
[00:09:32.200]we like it when those two say similar things
[00:09:34.690]but we were as low as 200 pounds of biomass
[00:09:37.310]in our first terminations at the Shelby site,
[00:09:39.780]which is here behind me.
[00:09:41.650]And then Arlington we were up to around three or 400
[00:09:44.700]and then up to 600 at our Eastern Nebraska Research
[00:09:47.660]and Extension Center Location.
[00:09:49.310]And we finished off around 2000 pounds
[00:09:51.610]at Eastern Nebraska Research and Extension Center
[00:09:54.090]and we cleared that 1000 pound mark,
[00:09:55.770]which is critical for seeing benefits from cover crops
[00:09:59.100]and so we just reached that in our final terminations
[00:10:02.440]for each of the Arlington and Shelby sites.
[00:10:05.700]So no surprise to any of us there are a lot
[00:10:07.450]of defoliators that can be found in soybeans.
[00:10:09.360]There are plenty this year that we're seeing
[00:10:11.490]fissile caterpillar is a common one it's been really spotty
[00:10:14.240]in the state this year,
[00:10:15.980]out near the Plattsmouth area there are hot spots,
[00:10:18.230]other places it's really hard to find it.
[00:10:21.010]We have anything from green clover warm on there,
[00:10:24.360]to yellow-striped armyworm to skippers,
[00:10:27.790]so lots of different things that can show up in the system.
[00:10:30.580]We typically don't focus on any one given insect
[00:10:34.700]that's a defoliator but on the large amount
[00:10:37.140]more on the plant response
[00:10:38.960]and how defoliated those plants are.
[00:10:40.850]So this infographic you see here
[00:10:42.640]which you can get in UNL crop watch web site
[00:10:46.010]shows you how to sample
[00:10:47.810]for defoliators in the system.
[00:10:50.150]It's important to take both the top, middle
[00:10:52.350]and bottom part of the canopy.
[00:10:53.900]Japanese beetle likes to hang in the top
[00:10:55.660]and defoliate the top it looks bad from the road
[00:10:58.230]but typically we've got a lot of undefoliated leaves
[00:11:01.330]below that that are capturing light
[00:11:03.330]and soybeans are incredibly good at compensating.
[00:11:06.130]And then other things you know we look at clover worms
[00:11:08.790]or loopers they like to hang lower in the canopy.
[00:11:10.770]So it's important to scout that whole canopy.
[00:11:13.070]The other tricky thing is to estimate
[00:11:15.220]the defoliation that's there,
[00:11:16.810]there's a little chart on the bottom there
[00:11:18.130]that shows you how to do that
[00:11:20.187]and so be sure to estimate that.
[00:11:22.270]Likely when you start doing this you're overestimating
[00:11:24.630]so maybe doc yourself a few percentage points
[00:11:27.110]as you go through that.
[00:11:28.830]So this graph is not missing information
[00:11:31.080]it just shows you how low the defoliation was this year.
[00:11:34.720]We had no significant defoliation to any site.
[00:11:37.470]This is early in the season
[00:11:38.850]this is during our vegetative stages
[00:11:40.940]where the amount of defoliation we can receive
[00:11:44.030]can be up to 30% without requiring any treatments,
[00:11:47.250]and so we had no treatment reach threshold
[00:11:49.240]below 5% on every single plot
[00:11:51.380]and that's been the same for the last two years.
[00:11:53.280]So that's great news,
[00:11:55.280]you know, that we're not seeing a lot of pressure.
[00:11:56.730]We're not seeing a lot of differences amongst
[00:11:58.240]our different treatments
[00:12:00.300]but we are certainly seeing some beneficial insect activity
[00:12:03.190]in those treatments that you'll see here now.
[00:12:07.110]And so we're consistently finding arthropods
[00:12:08.900]at all of our treatments across all sites and all years
[00:12:11.860]we have a lot of insect activity early in the season.
[00:12:14.960]A lot of these are beneficial
[00:12:16.660]so it's pretty apparent from this graph
[00:12:18.233]we have an increase in the number of beetles
[00:12:21.440]that we're seeing in the system as we delay termination.
[00:12:24.080]This is spotty on and off, year to year, site to site,
[00:12:27.690]flies vary a lot
[00:12:28.990]typically these aren't a problem in the system.
[00:12:30.860]We have some parasitoid activity
[00:12:32.480]that goes up with later termination dates which is great.
[00:12:35.460]They're specific to a lot of aphids
[00:12:36.960]and other things that might be present on cereals,
[00:12:39.670]the right cover crop when it's terminated.
[00:12:41.814]Ants are showing up in these systems as well as crickets,
[00:12:45.440]which don't injure our crops
[00:12:47.750]and then spiders bounce around a lot.
[00:12:50.330]So for details on each given location
[00:12:53.170]go to the booklet, look through,
[00:12:54.660]you'll see each individual site
[00:12:56.850]and you'll see the amount of variability
[00:12:58.320]between those sites.
[00:12:59.560]Some we got very strong response in terms of spiders,
[00:13:02.030]others not so much.
[00:13:03.580]And then millipedes which are almost never a problem
[00:13:06.180]they can be but it's very rare
[00:13:08.120]that they show up as a problem in these systems.
[00:13:11.610]So we're also asked by the Nebraska Soybean Board
[00:13:14.210]which funded this study to look at soybean biomass,
[00:13:16.750]which is pretty interesting a component to look at.
[00:13:19.760]We saw reduced biomass,
[00:13:21.490]soybean biomass for later termination dates at two sites.
[00:13:24.550]We did see this last year, this may concern you
[00:13:27.310]but it never pans out to yield
[00:13:28.710]at least it hasn't yet at the end of the season.
[00:13:31.010]So all these plants are a little bit smaller
[00:13:33.020]maybe in total size or biomass,
[00:13:35.380]it doesn't seem to impact final yield.
[00:13:37.150]So this is a good learning lesson let's not be concerned
[00:13:39.700]what we see early in the season
[00:13:41.310]wait till those final yields before we draw any
[00:13:43.780]potential conclusions or anything like that.
[00:13:46.960]So as a summary for cover crops and arthropods,
[00:13:49.480]we see both pest and beneficial insects
[00:13:51.780]in our cover crop systems each year in Nebraska
[00:13:54.310]and this is being done
[00:13:55.770]on a larger scale across seven other states.
[00:13:58.580]Nobody has documented any significant pressure
[00:14:00.900]from transition to these systems.
[00:14:02.840]So this is a good thing to incorporate into a system
[00:14:04.960]if you feel the need to and you don't need to add
[00:14:07.440]any insecticides to that system
[00:14:08.943]because we don't see a threat.
[00:14:11.420]Scout for those key pests anyway,
[00:14:13.360]every year is a little bit different.
[00:14:15.310]Degree day models are helpful for knowing when to scout.
[00:14:18.070]Don't routinely add tank mixed insecticides,
[00:14:20.760]we have studies going on that.
[00:14:22.130]We see a reduction in beneficial insects
[00:14:24.060]when those are used,
[00:14:25.480]and then the risk of or benefit of insects
[00:14:28.400]in an system varies from year to year in location.
[00:14:30.790]So it's just important to get out there,
[00:14:32.410]look especially in that transition period,
[00:14:34.710]as we get further in the season like now
[00:14:36.865]we're kind of out of any impact from that system
[00:14:39.940]because insects move a lot,
[00:14:41.290]unlike some of the other things we deal with
[00:14:44.260]during the season.
[00:14:46.100]that's what I got.
[00:14:47.450]So two things to discuss,
[00:14:48.770]one the question was asked,
[00:14:50.680]what about insecticides as a tank mix
[00:14:52.860]with fungicides at the end of the season
[00:14:55.540]or towards the end of the season here
[00:14:56.890]or three or four stages.
[00:14:59.070]You know, I'm gonna across the field anyway
[00:15:00.520]it's cheap to throw something in
[00:15:02.270]why don't I just toss in an insecticide?
[00:15:05.330]Growers are finding the repercussions of that some are,
[00:15:07.840]we've got spider mites that are present
[00:15:09.690]in a large part of the state right now
[00:15:11.310]we're hearing a lot of different reports.
[00:15:13.830]Spider mites do get taken out by some insecticides
[00:15:16.530]but what we are more likely to do
[00:15:17.960]is take out some of the predators
[00:15:19.220]and other things that occupy those systems.
[00:15:21.340]And so you may find yourself visiting that field again
[00:15:23.480]because you caused a flare up of spider mites.
[00:15:27.270]So there's lots of reasons not to do that
[00:15:29.760]if we do have significant pest pressure
[00:15:31.411]that's a reason to maybe think about that,
[00:15:33.910]but that add a dollar or two or a couple dollars
[00:15:36.530]just to throw that in the tank
[00:15:38.690]really doesn't make a lot of sense.
[00:15:40.600]And as you saw from our graphs
[00:15:42.350]we just don't have a lot of pest pressure out there
[00:15:45.697]and a lot of these systems from defoliators.
[00:15:47.768]It's a rare case when I visit a field
[00:15:49.720]and even myself as an entomologist,
[00:15:51.690]I'll head to a field
[00:15:52.880]and I'll say man this field looks like
[00:15:54.240]it might need a treatment,
[00:15:55.640]by the time I get through the evaluation
[00:15:57.310]for percent of defoliation,
[00:15:59.390]I'm below 20% reproductive stage thresholds
[00:16:02.490]for treating those fields.
[00:16:04.190]So good to get out scout, you're above threshold
[00:16:06.303]then it makes sense.
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