Mid-season Soybean Diseases
n this episode, Michael and Tamra Jackson-Ziems explore soybean diseases such as Soybean Cyst Nematodes, frogeye leaf spot, Phytophthora, Pythium, and more. Also included is where to get help diagnosing soybean diseases.
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[00:00:02.950]Welcome to Crop Watch Podcast.
[00:00:05.400]A production of Nebraska Extension.
[00:00:12.560]Welcome to the Crop Watch Podcast.
[00:00:14.260]I'm Michael Sindelar,
[00:00:15.270]Cropping Systems Extension Educator.
[00:00:17.340]Today I'll be joined again by,
[00:00:19.630]sorry, I'll be joined again with...
[00:00:22.490]Tamra Jackson-Ziems will be joining me again,
[00:00:24.940]as soon as I can talk right.
[00:00:26.810]Anyways, today we're gonna be talking
[00:00:28.490]about soybean diseases.
[00:00:30.910]Hi Tamra, how are you doing?
[00:00:33.253]How are you, Michael?
[00:00:34.300]Oh, I'm doing great.
[00:00:35.490]Just getting a little tongue tied today it seems.
[00:00:39.660]So today we're gonna switch gears.
[00:00:41.960]Our last podcast was about corn,
[00:00:44.570]today we're gonna switch and talk about soybeans.
[00:00:48.210]So when we look back with soy beans.
[00:00:51.790]What are we looking at for seedling diseases
[00:00:54.510]or maybe soil borne diseases?
[00:00:55.910]What are our concerns there?
[00:00:59.340]Well, the unfortunate thing about seedling diseases
[00:01:02.980]and any of those soil borne pathogens,
[00:01:05.310]is if you've had them before you can have them again.
[00:01:08.820]And in parts of the state in particular,
[00:01:11.150]where we've got or had some wet weather,
[00:01:14.220]it's definitely not everywhere,
[00:01:15.530]we're pretty dry in some parts.
[00:01:18.180]Where we've had the wet weather,
[00:01:19.710]you can and wet patches and spots
[00:01:22.670]out in the field especially,
[00:01:24.900]that may have drainage issues,
[00:01:26.210]you can start seeing Phytophthora and Pythium.
[00:01:29.670]Both of those organisms are water molds.
[00:01:32.850]They like those wet conditions
[00:01:34.790]because they produce spores that swim in that water.
[00:01:39.170]And Phytophthora being the bigger threat,
[00:01:42.180]that's the one we worry more about.
[00:01:44.630]Because not only does it cause a seedling disease,
[00:01:46.990]it can actually infect and kill plants
[00:01:49.210]throughout the season,
[00:01:50.490]even full grown adult plants.
[00:01:52.830]And can be pretty, pretty devastating.
[00:01:55.480]So thankfully, we've got a lot of things
[00:01:58.210]to do in response to that disease.
[00:02:01.150]We've got resistant hybrids.
[00:02:03.400]We've also got tolerant hybrids
[00:02:05.460]that are effective at a low level
[00:02:07.430]against all the right races.
[00:02:11.540]This tongue tied thing is contagious.
[00:02:14.350]But the Rps genes,
[00:02:16.600]the resistance genes are more race specific.
[00:02:19.360]And so, trying Rps1c, Rps1k especially
[00:02:24.370]have been the most effective for us.
[00:02:26.850]But if you got a big problem,
[00:02:28.240]you still should consider
[00:02:29.480]a seed treatment fungicide for Phytophthora,
[00:02:32.600]which might mean adding something
[00:02:35.250]with higher rates of metalaxyl or mefenoxam.
[00:02:39.390]It's gotta be a higher rate for Phytophthora
[00:02:41.710]for it to be effective.
[00:02:42.780]And now we also have ethaboxam
[00:02:45.230]that is effective against Phytophthora.
[00:02:48.560]But, if you're on the other part of the state
[00:02:52.100]where it's been very dry,
[00:02:53.500]you're not out of the woods for seedling diseases.
[00:02:55.900]Because we are seeing
[00:02:57.500]some rhizoctonia root rot and stem rot.
[00:03:01.790]So that one can be active
[00:03:04.840]even in some of the drier conditions too.
[00:03:07.580]So if you're having trouble identifying those,
[00:03:10.930]just please send us a sample to Diagnostic Clinic,
[00:03:13.590]and it'll help you make management decisions next year.
[00:03:16.790]But the other thing we're seeing now too
[00:03:18.650]are some of the herbicide injuries.
[00:03:21.530]And some of the symptoms of herbicide injury
[00:03:24.630]can be confusing with seedling disease symptoms.
[00:03:27.800]So again, send those off to
[00:03:30.610]our Plant and Pest Diagnostic Clinic in Lincoln
[00:03:32.840]for help identifying what's going on there,
[00:03:35.680]and provide as much information as you can
[00:03:37.700]on field history back a year or so.
[00:03:40.510]And especially the distribution of these plants
[00:03:44.700]when you send them in.
[00:03:48.660]I know it's not a common source
[00:03:50.420]of irrigation in the state,
[00:03:51.820]it used to be more common.
[00:03:52.980]But furrow irrigation,
[00:03:54.760]Is that something people need to pay
[00:03:56.610]a little bit more attention for some
[00:03:57.970]of these soil borne diseases
[00:04:00.840]where they may have a higher risk?
[00:04:04.010]That's a good question.
[00:04:06.770]I don't know that anybody's really looked at that
[00:04:09.050]from a research perspective,
[00:04:11.290]but absolutely on the upstream end,
[00:04:14.260]where the part of the field
[00:04:16.720]where the water comes in first
[00:04:19.050]would probably stay wetter longer.
[00:04:21.960]I would imagine there would be greater risk in those fields
[00:04:25.457]for some of these seedling diseases too.
[00:04:29.460]So, definitely keep an eye there
[00:04:31.860]and in the lower spots where you may get some ponding.
[00:04:35.685]Good call, and be careful
[00:04:38.940]when you dig up those symptomatic plants.
[00:04:41.320]If there's rotted roots,
[00:04:42.530]which there will be if they're seedling diseases,
[00:04:45.470]they'll break off really easily.
[00:04:46.980]And so, you'll need a shovel
[00:04:49.250]to be careful and get the whole plant up.
[00:04:51.780]Right, is there a chance that we can see combinations
[00:04:54.610]of the soil borne diseases.
[00:04:56.750]Where you have both a stem rot and a root rot
[00:04:59.980]Absolutely, it's not uncommon at all
[00:05:04.320]to see multiple things going on.
[00:05:06.730]Including like Fusarium and Pythium,
[00:05:10.470]Phytophthora all at the same time.
[00:05:13.050]Because they're active during the same time period,
[00:05:15.620]and sometimes under the same conditions.
[00:05:17.880]So it can make it really challenging to tell what's there.
[00:05:22.300]And it's also why many of our seed treatments
[00:05:25.290]contain multiple modes of action as well.
[00:05:29.060]And if you start reading on what some of those tags say,
[00:05:33.220]you'll notice there's as many
[00:05:34.520]as four fungicides on that seed.
[00:05:38.790]And they're all from different classes of fungicides,
[00:05:42.600]so they act against different groups.
[00:05:45.190]And so that's trying to give you
[00:05:46.640]a broad spectrum of protection.
[00:05:50.720]Right, so white mold,
[00:05:54.810]what do we need to worry about or look for for white mold?
[00:06:00.140]Well, some of those soybean fields
[00:06:01.530]are looking really good.
[00:06:03.380]And so it's heartbreaking to think about white mold
[00:06:08.170]and what can happen.
[00:06:10.320]These hot dry conditions that we've had
[00:06:13.270]have been not favorable for things like white mold
[00:06:17.017]and some of the other diseases.
[00:06:19.500]But we should talk about it now,
[00:06:22.050]so people can think about it.
[00:06:23.980]And if you're in an area
[00:06:25.390]where you've had more of the white mold in the past.
[00:06:28.870]And last year 2019, people saw more white mold
[00:06:32.770]in some areas like in South Central Nebraska,
[00:06:35.410]where they may not have seen much before.
[00:06:38.100]Keep in mind that that fungus over winters
[00:06:41.250]for years in those little black structures
[00:06:44.100]on the ground or in the soil.
[00:06:46.410]And so, if conditions become favorable during flowering,
[00:06:50.990]that's a critical time period.
[00:06:53.640]The spores that are produced and released in little puffs,
[00:06:57.530]land on senescing or dying flower petals,
[00:07:01.500]and that's where that fungus infects.
[00:07:04.560]Consequently, that's the time period
[00:07:07.510]when it's best to treat with a fungicide
[00:07:10.880]if you think you need it.
[00:07:12.990]And so we don't have much resistance to white mold.
[00:07:17.230]And so, if you're growing in a scenario
[00:07:20.390]where you know you're at higher risk.
[00:07:21.920]Where you're getting early canopy closure,
[00:07:24.620]you've got a high planting population,
[00:07:27.380]a history of disease.
[00:07:31.350]It creates very high humidity
[00:07:33.270]and perfect conditions inside that closed canopy
[00:07:36.375]for infection to take place.
[00:07:38.920]And so when you have flowering occurring inside that canopy,
[00:07:44.390]that's a good time to treat with a fungicide.
[00:07:47.330]We also now have,
[00:07:49.380]some of our colleagues are working
[00:07:50.960]on a monitoring system for white mold,
[00:07:56.300]and also a prediction model.
[00:07:58.580]And so they're trying to use weather conditions
[00:08:01.510]and various areas to predict
[00:08:03.010]when white mold might be a threat.
[00:08:05.740]And so that's on a limited basis right now,
[00:08:09.320]if you wanna try that out.
[00:08:10.650]Later on I think that'll be available to everyone.
[00:08:14.940]But that's something I would consider.
[00:08:17.300]And so, if you still continue to have problems with it,
[00:08:21.580]remember, wide rows and I guess planting
[00:08:28.700]at population densities that are more appropriate,
[00:08:31.180]not overly dense will help.
[00:08:34.870]You may have heard that some herbicides help.
[00:08:37.680]Like I think it's Cobra.
[00:08:40.380]And the way those herbicides
[00:08:42.240]have reduced white mold in some fields,
[00:08:44.670]is that they cause defoliation.
[00:08:46.740]And it opens that canopy up a little bit,
[00:08:48.720]where you get a little bit better air movement,
[00:08:51.130]and it makes it more difficult
[00:08:52.470]or unfavorable for that fungus.
[00:08:54.920]We don't recommend use of that product to fight white mold.
[00:08:59.040]There's other ways that I think we can do that better.
[00:09:02.270]But if you're gonna make an application,
[00:09:04.910]there's a number of fungicides labeled for use.
[00:09:07.550]And we do have an efficacy table in the 2020
[00:09:12.070]and other versions of the guide
[00:09:13.990]for weed disease and insect management.
[00:09:18.640]Right, a lot of information on white mold,
[00:09:21.567]and some good ways to trying to manage it.
[00:09:25.090]Moving on, we've been talking about fungicides.
[00:09:28.830]So when I think about fungicides in soybeans,
[00:09:30.780]I think about frogeye leaf spot.
[00:09:32.830]I know it's a little early to start thinking
[00:09:34.490]about frogeye leaf spot.
[00:09:35.840]But our previous podcast we were talking about,
[00:09:40.270]effective use of fungicides
[00:09:44.040]and risk of resistance to diseases.
[00:09:48.480]What's that looking like for frogeye leaf spot?
[00:09:50.310]I noticed that it seems like every year,
[00:09:53.180]two or three more counties get added to our map
[00:09:56.450]that have fungicide resistant frogeye leaf spot.
[00:10:01.330]Well, that's right.
[00:10:02.360]And that's probably the worst news.
[00:10:05.770]In fact, now we have confirmed fungicide resistance
[00:10:10.340]to the group 11 QoI fungicides,
[00:10:13.570]those are what we used to call it strobilurins Commonly.
[00:10:17.330]And those have been confirmed in 10 Nebraska counties.
[00:10:23.420]And so, this is a critical piece of information
[00:10:27.560]that having fungicide resistance in an area,
[00:10:31.220]it means that those products suddenly
[00:10:34.250]are no longer effective for you.
[00:10:37.350]Now, we don't know yet how widespread these problems are.
[00:10:41.410]But we do know that we found it
[00:10:43.050]in every county that we sampled.
[00:10:46.330]This was not an expansive survey.
[00:10:48.660]This was going out trying to get samples
[00:10:51.870]as quick as we can for testing,
[00:10:53.550]and found it in every county we tested last year.
[00:10:57.540]We hope we can expand that effort this year,
[00:11:00.500]and do some more testing.
[00:11:03.950]It's not too early to talk about it though.
[00:11:06.470]There are some spots showing up
[00:11:08.280]on leaves in parts of the state,
[00:11:09.990]it's unclear if those are early frogeye
[00:11:13.980]or if it's more likely gonna be pholusdicta.
[00:11:16.810]There are some things that look like frogeye.
[00:11:19.730]So if you start seeing those spots,
[00:11:22.283]what you should be looking for for frogeye leaf spot,
[00:11:25.540]is the development of those little elliptical
[00:11:28.000]or round gray lesions in the upper leaves
[00:11:31.760]of the soybean plants.
[00:11:33.450]And they have a dark brown or a purple margin around them.
[00:11:37.970]And in susceptible hybrids,
[00:11:40.530]of course, if they become severe,
[00:11:43.700]they can cause leaf area loss and of course yield loss.
[00:11:48.470]If you think you need a fungicide,
[00:11:51.360]please consider the active ingredients now
[00:11:54.650]that are in those products.
[00:11:56.520]We believe you'll get much better results
[00:11:58.780]using products that have two or more active ingredients
[00:12:02.990]that are effective.
[00:12:04.480]And so, now you have to consider
[00:12:06.530]the other classes of fungicides,
[00:12:09.870]like the triazoles, the SDHIs.
[00:12:13.270]And that might mean some of our three way fungicides
[00:12:16.200]might be good options as we start
[00:12:18.700]to battle this fungicide resistance.
[00:12:21.170]But only after you've done some scouting
[00:12:23.410]and know that you've got it out there.
[00:12:26.840]We wanna make sure and caution people on that,
[00:12:29.920]because using fungicides as a blanket application
[00:12:34.530]on all your acres,
[00:12:35.430]it's not a good idea anymore in some of these diseases.
[00:12:40.450]We have fungicide resistance now in frogeye leaf spot.
[00:12:44.470]Other states are now reporting fungicide resistance
[00:12:47.530]in other soybean diseases.
[00:12:49.890]And we haven't been testing that,
[00:12:53.060]and so it's unknown if that's going on here in Nebraska too.
[00:12:57.610]Like in the brown spot or cercospora leaf blight
[00:13:02.710]that leads to purple seed stain later on.
[00:13:06.730]So there's a lot of reasons for responsible fungicide use,
[00:13:10.230]so we can keep using the products
[00:13:11.720]that are helping us manage diseases.
[00:13:17.110]So looking at soybeans with the storms coming through,
[00:13:19.900]with high winds, driving winds and hail.
[00:13:23.490]Is there anything we need to keep an eye out for soybeans.
[00:13:27.020]Especially since they're at a,
[00:13:28.850]you know, they've been at somewhere
[00:13:30.250]between a V2 to V4 stage
[00:13:33.480]when the storms that rolled through.
[00:13:36.390]Good point, Michael.
[00:13:37.510]So like in corn, we talked about bacterial diseases
[00:13:42.790]that we see often develop after some of these storm events.
[00:13:46.740]The same thing can happen in soybean too.
[00:13:49.480]And many people might remember last year,
[00:13:51.870]we saw a lot of brownish yellow lesions on leaves,
[00:13:55.930]and much of that turned out to be bacterial leaf blight
[00:13:59.070]or bacterial blight on soybean.
[00:14:02.350]Very common diseases, bacterial blight, bacterial postural,
[00:14:06.530]we can start seeing some of those things develop
[00:14:09.050]in soybean too.
[00:14:10.830]And so, I'd be watching for that
[00:14:13.270]after areas have some of these heavy rains
[00:14:16.680]and storms move through.
[00:14:18.770]But sometimes even irrigation,
[00:14:20.960]we're providing enough moisture in the canopy
[00:14:23.290]for some of those diseases to develop.
[00:14:25.580]So I don't think we're out of the woods,
[00:14:28.290]and even in some of the drier areas.
[00:14:32.090]Alright, well, moving on to another not fun topic,
[00:14:36.600]Soybean Cyst Nematode.
[00:14:39.150]What do we have for updates for that?
[00:14:43.220]You know, I think we've talked for several years
[00:14:45.810]about Soybean Cyst Nematode now.
[00:14:48.140]And I wanna reiterate too
[00:14:52.650]that the nematode's still out there,
[00:14:54.620]and people should still be conscientious about it.
[00:14:59.030]And not Just as the nematode potentially
[00:15:02.530]can cause yield loss of 230% in some fields.
[00:15:06.930]And in those cases,
[00:15:07.980]you may not even be able to see symptoms
[00:15:11.080]other than the yield loss itself.
[00:15:13.080]And so if people are not achieving the yields
[00:15:16.340]that they're expecting,
[00:15:18.700]that could be a potential reason.
[00:15:20.440]Just remember though,
[00:15:21.440]that you can collect a sample of soil
[00:15:25.320]for nematode analysis,
[00:15:26.850]for Soybean Cyst Nematode analysis.
[00:15:29.400]In Nebraska, in fact it's free.
[00:15:31.540]And so, if people choose to do that,
[00:15:34.680]to collect the soil sample and submit it to us
[00:15:37.170]at the UNL Plant Pest Diagnostic Clinic for SCN analysis.
[00:15:41.710]And knowing what your population densities are,
[00:15:45.600]and knowing which fields are affected,
[00:15:47.850]is also important.
[00:15:49.050]Because that nematode can also affect other diseases
[00:15:52.490]that are becoming increasingly important to us in Nebraska.
[00:15:56.540]Like Sudden Death Syndrome and even brown stem rot too.
[00:16:03.250]Alright, how can you manage Soybean Cyst Nematode
[00:16:08.190]if you know you have in your system.
[00:16:09.800]What decisions are you thinking about through the year?
[00:16:13.210]And when do they start?
[00:16:14.640]I mean, are you thinking of them post harvest of corn
[00:16:18.010]and then moving on and planning?
[00:16:20.300]Or does it start at planting
[00:16:22.210]and then going through the growing season?
[00:16:25.740]That's a good question.
[00:16:28.200]And I think it applies to many of our diseases,
[00:16:30.820]when I say that you can manage
[00:16:33.190]most of these diseases starting in the wintertime.
[00:16:36.350]When you're making your seed selection,
[00:16:38.700]and you're making decisions about crop rotation.
[00:16:44.350]Those are very effective ways to manage many
[00:16:47.550]of these diseases that don't cost extra.
[00:16:50.830]And so, variety selection is very important.
[00:16:56.730]Soybean Cyst Nematode becomes more difficult though.
[00:17:00.330]So consider that corn of course and other grassy crops
[00:17:04.830]and alfalfa are not hosts for the Soybean Cyst Nematode.
[00:17:09.380]So if you've got a major problem with soybean cyst,
[00:17:12.420]rotating out of soybean for one, two, even more years,
[00:17:18.410]we'll help you knock that population back every year
[00:17:21.140]that you're out of beans.
[00:17:22.920]You won't completely eliminate them though.
[00:17:25.240]And so when you do come back to soybean,
[00:17:28.070]remember selection of resistant varieties of course,
[00:17:32.190]The complication is that most,
[00:17:34.900]and in fact, most of our varieties.
[00:17:38.460]over 95% of the resistant ones to soybean cyst,
[00:17:43.020]are derived from PI 88 788.
[00:17:45.830]A type of historic resistance
[00:17:47.840]that did a very good job for a long time.
[00:17:51.840]But across the country now and even in Nebraska,
[00:17:55.130]it's becoming less effective.
[00:17:57.020]That nematode adapts to that resistance.
[00:18:00.000]And So, if you can get a different source of resistance
[00:18:04.000]like Peking or 437 654,
[00:18:09.370]that would help you break up that lifecycle of the nematode.
[00:18:13.670]And it's just difficult in some of the maturity groups
[00:18:17.260]to find some of those other sources of resistance
[00:18:19.770]here in the state.
[00:18:21.710]So that puts the pressure on us to do a better job rotating,
[00:18:26.270]and also with seed treatment nematicides
[00:18:28.980]that are available now for soybean cyst.
[00:18:32.240]And using a combination of those practices
[00:18:36.030]probably gonna help you
[00:18:36.863]do the best job managing the nematode,
[00:18:40.180]and thus managing other diseases that it impacts.
[00:18:44.410]Alright, when we're thinking about Sudden Death Syndrome,
[00:18:49.690]is there anything when we look at past years
[00:18:52.393]that we can use to help us for new seasons
[00:18:54.890]or even for this season
[00:18:56.828]to help manage Sudden Death Syndrome?
[00:19:00.183]Absolutely, we have good news about that.
[00:19:04.862]So soybean Sudden Death Syndrome or SDS we call it,
[00:19:09.580]it has become more important to us in recent years.
[00:19:12.890]We in fact, after last year in 2019 when it was so wet,
[00:19:17.200]we saw a lot more sudden death syndrome in some areas,
[00:19:20.310]and in new areas where people may not have seen it before.
[00:19:23.990]And so, that disease as you may remember,
[00:19:27.200]is in patches out in fields.
[00:19:28.980]It's caused by another soil borne fungus,
[00:19:32.050]a species of Fusarium.
[00:19:34.320]And when the nematode is present,
[00:19:37.680]it can make SDS both show up earlier than it would
[00:19:41.160]if the nematode wasn't there.
[00:19:42.510]And it can also become more severe
[00:19:44.820]than if the nematode wasn't there.
[00:19:46.890]And so, be sure and manage
[00:19:48.730]your Soybean Cyst Nematode populations.
[00:19:51.540]But also once you've had Sudden Death Syndrome,
[00:19:54.550]again, it's there perpetually.
[00:19:56.790]And so you should continue
[00:19:58.500]to consider SDS resistant varieties.
[00:20:02.210]In fact, management of SDS is 80% variety selection.
[00:20:09.410]And we know we can improve yields,
[00:20:11.340]there's 80% difference between having a susceptible
[00:20:14.000]and a resistant variety.
[00:20:15.990]But also, we now have seed treatments available
[00:20:20.060]for management of SDS.
[00:20:22.260]And so if you're seeing a lot of SDS,
[00:20:25.070]and covering higher proportions of fields,
[00:20:28.180]adding one of those seed treatments
[00:20:30.080]that are effective against SDS like a ILeVO
[00:20:34.560]can help on top of the resistance,
[00:20:36.760]give you the best chance
[00:20:37.920]of reducing disease severity of SDS.
[00:20:40.980]So that's really good news.
[00:20:43.590]And we've got other products now too,
[00:20:45.910]that are becoming available,
[00:20:47.400]that we're also testing.
[00:20:48.600]And so we'll have more data on that as we move forward.
[00:20:51.990]Alright, sounds like there's
[00:20:53.120]a lot of off-season decisions that can really help you out
[00:20:56.220]when you're looking at Sudden Death Syndrome.
[00:21:01.490]So with that once again,
[00:21:03.610]this is another podcast chocked full of information
[00:21:06.760]that some people may need more than one time
[00:21:09.350]through to digest.
[00:21:13.150]Any other general thoughts before we wrap up the podcast.
[00:21:17.780]I appreciate everyone tuning in.
[00:21:20.210]And wanna remind everyone,
[00:21:22.240]we have a lot of resources and people
[00:21:24.330]that are available to help.
[00:21:26.070]And so if anyone has trouble diagnosing a disease
[00:21:28.820]or has questions,
[00:21:29.950]we have resources.
[00:21:32.020]We have the UNL Plant and Pest Diagnostic Clinic,
[00:21:34.640]and folks in Nebraska Extension like Michael and I,
[00:21:38.120]and those in your own counties that can help.
[00:21:42.510]Well, thanks for dropping by today Tamra.
[00:21:46.790]Hopefully we'll have another great growing season.
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