4 - 2020 Soybean Management Field Days - Soybean Cyst Nematodes Update

Nebraska Soybean Board & Nebraska Extension Author

09/25/2020 Added

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A look at soybean diseases with emphasis on Soybean Cyst Nematode updates with Tamra Jackson-Ziems, Nebraska Extension Plant Pathologist

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[00:00:01.084](Upbeat music)
[00:00:07.180]Hi, I'm Tamara Jackson-Ziems Extension Plant Pathologist
[00:00:10.250]at the University of Nebraska Lincoln.
[00:00:13.310]Today I want to talk to you about
[00:00:14.970]a number of soybean diseases
[00:00:16.660]but especially focusing on Soybean Cyst Nematode.
[00:00:20.300]And you may sit there and think
[00:00:22.300]that we've maybe we've beaten Soybean Cyst Nematode
[00:00:26.070]like a dead horse
[00:00:27.110]but the reality is that's not the case
[00:00:30.790]because we actually have noticed that there's evidence
[00:00:34.290]that we're actually falling behind
[00:00:36.000]and that we're not managing
[00:00:37.810]Soybean Cyst Nematode nearly as well as we used to.
[00:00:41.050]And so I think for many people
[00:00:42.870]soybean cyst has become out of sight and out of mind.
[00:00:45.910]And I want to talk to you about why we need to make sure
[00:00:49.530]and consider soybean cyst
[00:00:51.360]in our regular routine and variety selection, et cetera.
[00:00:56.050]So Soybean Cyst Nematode is a pathogen
[00:00:58.420]that we've known for decades, and we've also known
[00:01:01.010]for a long time that it can cause serious yield loss.
[00:01:04.250]In fact they've documented up to 30% yield loss
[00:01:07.330]with no measurable or visible symptoms
[00:01:11.730]other than what you might experience
[00:01:13.520]at the end of the season during harvest and yield loss.
[00:01:16.960]I want to emphasize that now middle
[00:01:19.160]of the season is a great time for you to go out
[00:01:21.730]and carefully dig up roots and examine them.
[00:01:24.650]Look for the small white females.
[00:01:26.850]These females are very small.
[00:01:28.570]They're lemon shaped.
[00:01:29.810]They're a lot smaller than the nitrogen fixing nodules
[00:01:32.670]that you can see on those roots.
[00:01:35.050]In addition, you can collect soil samples
[00:01:37.700]for Soybean Cyst Nematode analysis, any time of year
[00:01:41.230]and in any crop, because that nematode stays
[00:01:44.590]in the upper eight to 10 inches of the soil.
[00:01:47.790]And so you're guaranteed to find them in soil samples,
[00:01:50.900]just to make sure that you're sampling from within the row
[00:01:53.880]and send those to the UNL plant
[00:01:55.790]and pest diagnostic clinic and samples coming in
[00:01:58.360]from Nebraska will be processed for free.
[00:02:05.020]I also want to emphasize that we know
[00:02:06.870]that Soybean Cyst Nematode is widely distributed
[00:02:09.410]in our soybean producing counties in Nebraska.
[00:02:12.230]And so in the map that I'm showing
[00:02:13.930]on the right side of this slide, we've got
[00:02:16.180]over 50 counties that have been documented to be infested
[00:02:19.480]with the nematode.
[00:02:20.900]Now that doesn't necessarily mean
[00:02:22.400]that every field is affected.
[00:02:24.050]And you won't know until you collect samples
[00:02:26.970]because like I mentioned earlier, you may not see symptoms.
[00:02:29.750]If you are seeing symptoms
[00:02:31.210]there's a good chance that the symptoms could be severe
[00:02:34.190]and you may have a very high population density.
[00:02:37.780]It's important to remember the management strategies
[00:02:40.420]that we've got available to us though.
[00:02:42.570]The primary one that we discussed is the use
[00:02:45.010]of rotation and that's rotation with non host crops.
[00:02:49.920]Clearly corn is the most commonly planted
[00:02:52.860]non-host crop in Nebraska,
[00:02:54.810]but any grassy crop, including any
[00:02:56.920]of our small grains or even alfalfa make good crop rotations
[00:03:01.050]for soybean cyst, because the nematode is not able to infect
[00:03:05.420]and set up a feeding site and reproduce.
[00:03:08.930]Well that's the same strategy
[00:03:10.500]when we recommend the management
[00:03:12.760]of susceptible winter annual weeds.
[00:03:15.900]And that'll be coming up in the next few weeks
[00:03:18.310]because many of those need to be managed in the fall.
[00:03:21.280]Some of the species that we have here
[00:03:23.240]in Nebraska that are also susceptible
[00:03:25.360]to Soybean Cyst Nematode are henbit purple dead nettle.
[00:03:28.861]And you'll know those
[00:03:30.740]because of the purple haze that you see
[00:03:33.210]in some of the fields in the spring
[00:03:36.700]feel pennycress, common Chiquita or even Shepherd's purse.
[00:03:39.740]Any of these weeds can be host to soybean cyst.
[00:03:42.930]And so what that means is under warmer conditions
[00:03:46.160]we can begin to see reproduction of the nematode lb.
[00:03:49.010]It usually slower
[00:03:50.360]than what we would see during the regular growing season.
[00:03:53.490]And so it's important to manage those as well.
[00:03:56.540]Finally, last but certainly not least
[00:03:59.120]is the use of resistant varieties.
[00:04:02.030]And we have a lot of resistant varieties available to us.
[00:04:05.890]What you might not realize is
[00:04:07.620]that almost all over 90% of our resistant varieties
[00:04:11.540]for soybean cyst are derived from a single line PI 88788.
[00:04:18.600]PI 88788 has resistance,
[00:04:21.130]that's across several genes.
[00:04:23.430]Unfortunately using conventional breeding techniques
[00:04:26.360]all varieties, don't have all of those genes for resistance.
[00:04:30.230]And so it's unknown often how much it's got
[00:04:33.670]until you look at some of the ratings
[00:04:35.330]and it's important that you select among them
[00:04:37.470]because some of them are more resistant than others.
[00:04:40.290]And it makes a big difference.
[00:04:42.790]One of the other things you should remember is
[00:04:44.760]that in addition to changing resistance,
[00:04:48.180]and if you have other sources of resistance,
[00:04:50.360]do that as well.
[00:04:51.740]But even just changing varieties is also important
[00:04:55.050]because this nematode can adapt not only
[00:04:57.820]to the source of resistance
[00:04:59.200]but there is some adaptation to the variety itself.
[00:05:02.870]And so remember that when you're making your selections
[00:05:06.010]in the winter time.
[00:05:07.600]We also now have seed treatment
[00:05:09.350]in the muddy sides available for management of soybean cyst
[00:05:12.350]that you can use on top of the other management strategies.
[00:05:15.780]And there's been some limited evidence
[00:05:17.770]that those are beneficial as well.
[00:05:20.860]A few things though, that we should keep in mind
[00:05:22.920]when you're selecting your resistant varieties.
[00:05:25.330]It's important to understand
[00:05:27.190]that they're not going to control all of the nematodes.
[00:05:30.750]Unfortunately we've documented
[00:05:32.510]in many States across the United States
[00:05:34.830]that nematodes soybean cyst particularly
[00:05:37.580]are adapting to even the PI 88788.
[00:05:42.150]It has been used for many years
[00:05:44.060]and widespread across the country and nematode populations
[00:05:47.930]in these States are adapting to it at a high rate.
[00:05:51.560]In fact, if you look at the graphic on the right hand side
[00:05:54.610]of the screen, you'll notice that
[00:05:55.830]in some States, especially in the
[00:05:57.440]Southern States where we've documented soybean cyst longer
[00:06:01.100]you'll notice that the percent
[00:06:02.580]of soybean cyst populations that are adapting
[00:06:05.440]to PI 88788 is very high.
[00:06:08.530]In fact, in Missouri 100% of the populations
[00:06:11.720]are already able to infect
[00:06:13.660]and reproduce on those resistant lines.
[00:06:16.830]Some States like Illinois are as high as 88%.
[00:06:20.620]In our area though, we are at 47%, just almost 50%
[00:06:25.380]of the populations, but you need to understand
[00:06:27.720]that these data were also estimated about a decade ago.
[00:06:31.630]And so they might be out of date
[00:06:33.680]and we would expect that this could continue to increase.
[00:06:36.940]And so you should keep in mind
[00:06:38.710]that you should continue
[00:06:40.000]to check your Soybean Cyst Nematode population densities
[00:06:42.940]by continuing the sample every two to four years
[00:06:46.760]to monitor for that.
[00:06:48.040]Especially if you begin to see yield loss
[00:06:50.550]and you can't explain it
[00:06:51.620]with any other reasonable explanation.
[00:06:55.560]You should also know that soybean cyst
[00:06:57.240]can impact other diseases
[00:06:59.060]in particular sudden death syndrome.
[00:07:01.300]And we've begun to see a little bit
[00:07:02.860]of SDS showing up here lately in a few areas
[00:07:06.520]Soybean Cyst Nematode, when it's present can lead
[00:07:09.760]to sudden deaths, syndrome development earlier.
[00:07:13.080]And actually that disease can become
[00:07:14.900]more severe when the nematode is present.
[00:07:17.290]And so what that means is when
[00:07:18.930]you're selecting your resistant varieties
[00:07:21.190]it's important to select varieties that are resistant
[00:07:24.610]to both SDS and Soybean Cyst Nematode.
[00:07:28.870]In fact, we know from data coming out
[00:07:30.950]of collaborative regional projects across the country
[00:07:34.080]that resistant varieties for SDS give you 80% returns
[00:07:39.120]in yield in fields where you've got SDS.
[00:07:42.380]And that we now have seed treatments that work
[00:07:46.090]against sudden death syndrome, like the product
[00:07:48.610]of Ilevo those product of have given us 20% returns.
[00:07:52.390]And so they're often a good tool to use on top
[00:07:55.210]of the resistant varieties that we're already selecting.
[00:07:58.930]Please also remember other diseases
[00:08:00.480]like Brown Stem Rot can also be impacted by soybean cyst.
[00:08:04.030]And we're just beginning to learn more
[00:08:05.630]about these interactions.
[00:08:07.180]And so if you're unfamiliar
[00:08:08.540]with SDS, please contact us in Nebraska extension.
[00:08:12.110]The pictures on this slide will show you what some
[00:08:14.440]of the leaf symptoms look like.
[00:08:16.330]So look for interventional yellowing
[00:08:19.280]and necrosis as those areas die out.
[00:08:21.420]And it does defoliate plants very quickly.
[00:08:24.200]If you pull those plants up and look at the roots,
[00:08:26.630]you'll notice it also causes severe root rot.
[00:08:28.990]And when they're split open
[00:08:30.530]the lower stems can be very discolored
[00:08:32.700]especially in the outer cortex region.
[00:08:37.550]Another disease I want to mention
[00:08:39.090]briefly is Frogeye leaf spot.
[00:08:41.270]That disease is also developing right now.
[00:08:43.970]It's important for us to get out
[00:08:45.560]and look for that disease.
[00:08:47.260]I hope in addition to this presentation,
[00:08:49.320]you'll also watch a video
[00:08:50.860]from UNL graduate student Asha Mane
[00:08:54.000]because she'll give you more information
[00:08:55.760]about Frogeye leaf spot,
[00:08:57.730]as well as a project that she's doing
[00:08:59.530]for her dissertation research.
[00:09:01.240]That's going to help all of us soybean growers.
[00:09:04.420]You need to understand those, especially
[00:09:06.630]that we have documented group 11 Q-O-I fungicide resistance
[00:09:11.360]in the Frogeye leaf swap pathogen
[00:09:13.390]right here in Nebraska.
[00:09:15.300]The 10 counties where we've confirmed it
[00:09:17.270]are in the map on the right hand side
[00:09:19.230]and highlighted in yellow.
[00:09:20.890]But you should understand
[00:09:22.310]that these are the only 10 counties that we sampled
[00:09:25.390]and we detected resistance in every one of those counties.
[00:09:29.310]It's unknown how widespread the distribution
[00:09:31.780]of that resistance is beyond those counties,
[00:09:34.470]but we are grateful acknowledged the support
[00:09:36.870]from our Nebraska soybean board,
[00:09:38.410]that's going to help us continue that survey and expand it
[00:09:41.850]so that we can find out exactly how widespread that is
[00:09:45.390]and may help you make better management recommendations.
[00:09:49.390]We need your samples though, from across the state
[00:09:52.040]because we want to get Frogeye leaf spot samples
[00:09:54.900]from all the counties growing soybeans
[00:09:57.290]in the state so that we can have those tested for free.
[00:10:00.410]And so if you have samples to submit,
[00:10:02.020]please contact us in Nebraska extension.
[00:10:06.020]Summarizing this presentation.
[00:10:08.050]I want to remind you, it is still important
[00:10:10.170]that we continue to manage for soybean cyst damage caused
[00:10:13.360]by the nematode is apparently increasing.
[00:10:15.890]As people become more complacent about this nematode.
[00:10:19.960]Please remember to also select resistant varieties
[00:10:22.550]to sudden death syndrome.
[00:10:23.760]If you've seen that disease
[00:10:24.990]in the past or beginning to see it develop now
[00:10:27.690]and if you're seeing Frogeye leaf spot development
[00:10:30.940]in your fields remember this is going
[00:10:32.830]to impact fungicide selection.
[00:10:36.000]The fact that we've confirmed resistance here in Nebraska.
[00:10:39.070]And so if you have questions about these
[00:10:41.270]or any other topics, please contact us
[00:10:43.810]in Nebraska extension for more information.
[00:10:46.180]Thank you.
[00:10:47.870]When you're considering sampling for Soybean Cyst Nematode
[00:10:50.550]remember using a traditional soil probe
[00:10:53.440]to a depth of about eight inches
[00:10:55.340]is adequate for sampling for this nematode.
[00:10:58.100]Just remember that we need about two cups,
[00:11:00.960]cumulatively from soil from about 40 acres,
[00:11:03.970]and be sure to collect those samples
[00:11:05.630]from within the road to make sure
[00:11:07.350]that you're capturing nematodes that
[00:11:09.280]are on that root debris.
[00:11:11.150]And in addition, keep in mind because this nematode stays
[00:11:14.820]in the upper eight inches of the soil.
[00:11:16.590]You can sample in any crop at any time of year.
[00:11:20.200]Just be sure to request a Soybean Cyst Nematode sample.
[00:11:24.410]We have a question about Frogeye leaf spot.
[00:11:26.860]If you see Frogeye leaf spot development
[00:11:28.920]in your fields, and you'd like to submit a sample
[00:11:31.220]for the survey that we're conducting.
[00:11:33.470]You'll notice those symptoms are going to likely develop
[00:11:36.210]on the upper leaves
[00:11:37.530]and there'll be circular or elliptical gray
[00:11:40.350]in color usually, and have a dark margin around them.
[00:11:43.840]If you want to submit a sample
[00:11:45.060]be sure and collect up to about 10 symptomatic leaves
[00:11:48.450]and place them in a plastic bag.
[00:11:50.770]Please ship them rapidly to our office
[00:11:53.090]at the UNL plant and pest diagnostic clinic for testing.
[00:11:56.490]And if you'd like to have some of our sampling envelopes
[00:12:00.060]please let us know and we'll provide those.
[00:12:02.750]And the shipping will be free on those.
[00:12:05.960]Recently we've had questions
[00:12:07.600]about the use of foliar fungicides in soybeans
[00:12:11.000]with or without disease presence
[00:12:14.540]at the University of Nebraska extension.
[00:12:16.730]We don't recommend the use of foliar fungicides
[00:12:19.590]for use other than to manage diseases.
[00:12:22.450]One of the big reasons for that is
[00:12:24.210]the potential development
[00:12:25.940]of resistance to some of those products.
[00:12:27.960]And we're already seeing
[00:12:29.060]that in our Frogeye leaf spot pathogen,
[00:12:31.670]in other States they're also seeing it
[00:12:33.610]in additional pathogens
[00:12:35.320]once like Brown Spot, Septoria causes
[00:12:38.530]that one and others as well.
[00:12:40.540]Like the one that causes Cercospora leaf blight.
[00:12:43.200]And although we haven't documented that in Nebraska
[00:12:45.670]it's possible that we could also be driving resistance
[00:12:48.710]to fungicides in those pathogens and others as well.
[00:12:52.840]When you're considering a fungicide for use in soybean,
[00:12:55.940]keep in mind that the products where
[00:12:57.690]we've documented fungicide resistance
[00:13:00.260]or what we've traditionally called
[00:13:01.790]the Strobilurin products.
[00:13:03.510]These are actually group 11 Q-O-I products
[00:13:06.160]as we refer to them now
[00:13:07.880]and those products have historically been
[00:13:09.810]the most effective for management of Frogeye leaf spot.
[00:13:13.760]The best applications for management of Frogeye
[00:13:16.650]that are going to work the best
[00:13:18.010]are going to be made around hour three
[00:13:20.050]and hour four
[00:13:21.120]Keep in mind though that most
[00:13:23.300]of these products are going to only provide protection
[00:13:26.110]for about 21 days.
[00:13:28.250]And so it's important to have the application timed to well
[00:13:31.520]so that you get the maximum benefit
[00:13:33.150]from the protection that it provides.
[00:13:36.100]Right now we're also receiving a lot
[00:13:37.700]of questions about the use of fungicides
[00:13:40.070]and disease, economic thresholds for treatment.
[00:13:44.230]Unfortunately, we don't have economic thresholds
[00:13:47.030]for many of our diseases because many of those decisions
[00:13:50.870]and whether or not disease severity increases
[00:13:53.380]to a critical level is dependent on factors other
[00:13:56.790]than how much disease is present at the time.
[00:13:59.500]For example, the rating, the hybrid or variety rating
[00:14:02.840]of that soybean variety can also tell you
[00:14:05.680]and help you anticipate how severe that disease might come.
[00:14:09.330]In addition, you should also consider the history of most
[00:14:12.150]of these diseases, including Frogeye or even white mold
[00:14:16.030]and the biology of them and how they infect the plan.
[00:14:21.470]For example, white mold is a disease
[00:14:24.290]that you may not see until later in the season,
[00:14:26.430]but the best treatment should have occurred around flowering
[00:14:29.650]because infection occurs in
[00:14:31.010]the senescent flowers earlier in the season.
[00:14:33.820]In contrast though, a disease like Frogeye leaf spot tends
[00:14:36.960]to develop a little bit later,
[00:14:38.570]often around hour two or three.
[00:14:41.200]And so that timing is usually
[00:14:43.460]the best time to apply a fungicide
[00:14:45.500]to control that particular disease,
[00:14:47.960]but they're all dependent on weather as well.
[00:14:50.430]And so monitoring weather forecasting
[00:14:52.670]will help you anticipate
[00:14:54.090]if those diseases are going to increase
[00:14:55.940]to a critical level as well.

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4 - 2020 Soybean Management Field Days - Soybean Cyst Nematodes Update

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