Mid-season Disease in Corn and Soybean

Michael Sindelar and Tamra Jackson-Ziems Author

06/25/2019 Added

3 Plays

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Corn nematodes, bacterial leaf streak, and frogeye leafspot, oh my! Tamra Jackson-Ziems returns to the Nebraska CropWatch Podcast with information on mid-season corn and soybean diseases. Listen in if you are interested in knowing more about the three.

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[00:00:00.484](upbeat music)
[00:00:02.960]Welcome to CropWatch Podcast,
[00:00:05.410]a production of Nebraska Extension.
[00:00:12.360]Welcome to the CropWatch Podcast.
[00:00:14.290]I'm Michael Sindelar, cropping systems extension educator.
[00:00:17.200]For today's CropWatch Podcast, we'll be talking about
[00:00:20.230]corn and soybean diseases in the mid-season.
[00:00:22.810]Today I'll be joined by Dr. Tamra Jackson-Ziems.
[00:00:27.390]Dr. Jackson, would you like to introduce yourself more?
[00:00:30.640]I'm sorry, Dr. Jackson-Ziems.
[00:00:33.320]That's quite all right.
[00:00:34.153]Yes, my name is Tamra Jackson-Ziems
[00:00:37.610]and I am an extension specialist for Nebraska Extension,
[00:00:41.610]covering diseases of corn and grain sorghum
[00:00:44.450]statewide in Nebraska, as well as soybean diseases.
[00:00:48.760]So it has not been a very normal growing season so far.
[00:00:54.550]I think that can be put across the state.
[00:00:57.600]I'm out, I'm walking through stands of corn
[00:01:00.670]and some of them are finally starting to be very even
[00:01:03.840]but when I'm out walking through the cornfields,
[00:01:06.650]what are some of the things
[00:01:07.590]I should be starting to look at now
[00:01:08.970]since corn is starting to move through
[00:01:11.050]into that V5, maybe V7, if you were lucky
[00:01:14.372]with early season corn, what should I be looking for?
[00:01:17.940]Well, there's a lot of things of course
[00:01:19.770]that can go wrong out there and it's great to finally have
[00:01:23.600]a crop up in most of these fields.
[00:01:25.980]One of the things that I've gotten a lot of questions about
[00:01:29.340]this year and this spring especially
[00:01:31.530]is about nematodes affecting corn
[00:01:34.580]and when we talk about nematodes,
[00:01:36.920]most people think about soybean cyst nematode in soybean.
[00:01:42.110]But actually, there's a number of different species
[00:01:45.240]and genera that can affect corn
[00:01:47.324]and in Nebraska, we have a long history
[00:01:50.980]of having areas that have had nematode problems
[00:01:54.740]and now that we have a few new products becoming available
[00:01:58.270]in our toolbox as seed treatment nematicides,
[00:02:02.340]people are asking more questions about them
[00:02:04.440]and we're going back and reviewing some of those things
[00:02:07.410]that we haven't talked about in a while.
[00:02:09.480]So what would be the symptoms of nematodes?
[00:02:13.200]'Cause I'm guessing if you want to use a nemacide,
[00:02:16.420]it's best to know if you have a history
[00:02:18.640]of these nematodes in your field.
[00:02:21.115]Well, that's right and nematodes of corn
[00:02:24.567]are quite complicated in several ways
[00:02:28.100]and in particular, we're talking about
[00:02:31.145]eight or 10 different species, even genera,
[00:02:36.000]different types of corn nematodes.
[00:02:38.920]Some of those even feed on other crops
[00:02:41.180]like soybean or other sorghum
[00:02:43.640]or just about anything else you might plant.
[00:02:46.670]These nematodes feed in different ways,
[00:02:49.150]so they cause different types of damage
[00:02:52.020]and the types of damage they cause varies a lot
[00:02:55.740]and so the appearance and the symptoms
[00:02:57.780]that you might encounter may look different.
[00:03:00.780]And so unfortunately, we have a history of nematode damage
[00:03:07.601]and I think for decades, we've conditioned people to believe
[00:03:12.470]that you have these big, almost dead spots in a field
[00:03:17.340]where you've got severe stunting
[00:03:19.180]and that it's only in sandy fields,
[00:03:22.800]and much of that is based on misconceptions
[00:03:26.546]and I want to make sure people understand that.
[00:03:29.780]And the reality is that we've got nematodes
[00:03:34.100]like sting nematode and needle nematode
[00:03:36.883]that do cause that type of damage that's very severe
[00:03:41.170]and causes those very severely-affected areas in fields
[00:03:45.900]and you'll only see those on sandy fields,
[00:03:48.800]but the reality is is that there are a number
[00:03:51.260]of other nematodes that are much smaller in size
[00:03:55.055]relative to each other and they don't require sand.
[00:03:59.138]And so you can find plant parasitic nematodes,
[00:04:03.188]those are the bad guys, in every single field.
[00:04:07.520]And so what determines whether or not you have a problem
[00:04:11.400]depends on which ones you have and how many there are.
[00:04:14.710]And so I would look for areas of stunting
[00:04:18.015]or yellow plants and patches in the field.
[00:04:21.262]Be sure and carry your spade out to take a closer look
[00:04:24.840]and when you dig up some of those plants,
[00:04:26.610]if you see root damage on some of them,
[00:04:29.785]nematodes can cause some pretty severe root lesions
[00:04:34.590]or stubbiness or branching, there's a lot
[00:04:38.160]of different types of symptoms,
[00:04:39.670]and so from there, if you think you have nematode damage
[00:04:44.930]and your yields aren't meeting your goals,
[00:04:47.500]you might want to consider collecting a nematode sample
[00:04:50.560]and submitting it to a lab for analysis.
[00:04:53.530]So when I collect the sample,
[00:04:55.199]what are the labs in the local areas
[00:04:57.610]that I would want to submit these nematode samples to?
[00:05:01.058]In Nebraska, you have a couple of options
[00:05:04.177]and so our lab at the UNL Plant and Pest Diagnostic Clinic
[00:05:08.888]on the East Campus does accept
[00:05:11.806]and process nematode samples from corn.
[00:05:16.160]You need to be very clear that those samples are from corn
[00:05:19.597]and you want the nematodes analyzed
[00:05:22.070]that you might find from corn.
[00:05:24.020]It's a very different process
[00:05:25.630]than what we use for soybean cyst nematode
[00:05:28.508]and actually, when you look at those,
[00:05:31.347]you have to keep in mind too that you'll be charged
[00:05:35.340]for the ones that come from corn for corn nematode analysis.
[00:05:40.640]Those are gonna cost you about $40 per sample,
[00:05:44.040]whereas soybean cyst nematode analysis
[00:05:46.410]is free of charge right now.
[00:05:48.630]And the process being much different,
[00:05:51.130]that lab might need you to do something different.
[00:05:53.630]You may not just need to bring in soil.
[00:05:55.930]You might need to also collect
[00:05:58.000]additional small plants for a root analysis.
[00:06:01.588]And so when our lab processes them,
[00:06:04.193]we will run those samples as well
[00:06:07.346]or we'll take the tiny root fragments from your soil sample
[00:06:11.494]and when you're using that probe
[00:06:13.900]to puncture down along the row,
[00:06:16.210]you should be getting the roots in there.
[00:06:17.700]You should hear those roots popping and snapping
[00:06:20.210]as you collect those samples.
[00:06:22.310]We collect those root fragments out of there
[00:06:24.600]and then extract nematodes from them.
[00:06:27.744]I also forgot to mention, too,
[00:06:30.197]there's a second lab in Nebraska
[00:06:32.510]that will collect and process nematode samples
[00:06:36.060]and that is called Nema-Test in Lincoln, as well.
[00:06:39.980]There's also a few other labs in other states available.
[00:06:42.770]If you do send a sample out of state,
[00:06:44.910]it's important though that you let them know it's coming
[00:06:48.520]and you confirm that they have the federal permit
[00:06:50.960]that allows them to legally accept those samples.
[00:06:53.960]So, Tamra, some of the important takeaways
[00:06:56.580]from what you've discussed is that there are still
[00:06:59.980]some myths that are not true with corn nematodes,
[00:07:03.042]which are that they only occur in sandy soil
[00:07:07.002]and they're only found in large areas
[00:07:09.710]of die-off or stunted growth, so it's important
[00:07:12.270]to look and scout for these in non-sandy soils,
[00:07:15.730]even though the effects will probably be
[00:07:18.020]more visible in the sandy soils.
[00:07:20.480]Is that correct?
[00:07:22.240]Yes, that's correct.
[00:07:23.567]And there are nematodes in every field.
[00:07:26.220]Often, the worst damage they cause
[00:07:28.350]might be in those sandy fields.
[00:07:30.407]And I would argue that it might be more common
[00:07:33.528]to see moderate nematode damage
[00:07:36.387]that may just cause a little stunting and yellow plants
[00:07:40.530]and that would be a good place
[00:07:42.010]to start your scouting efforts
[00:07:43.920]and if you were choosing to collect samples,
[00:07:46.600]I think I would start there.
[00:07:48.440]We'll talk about the new kid on the block,
[00:07:51.776]the bacterial leaf streak.
[00:07:53.756]What are we looking for for this year
[00:07:56.380]and is this really gonna be one of the things
[00:07:58.850]people should be keeping their eyes out for?
[00:08:01.380]You know, this disease, bacterial leaf streak,
[00:08:03.710]is still pretty new to us.
[00:08:06.221]We've just only first confirmed it officially in 2016
[00:08:10.861]but it is quite widespread.
[00:08:14.350]We've actually confirmed the pathogen
[00:08:16.600]in samples from 74 Nebraska counties since 2016
[00:08:21.789]and so it's over most of the state,
[00:08:24.935]although it's much more common in some areas than in others.
[00:08:29.064]And so what I would watch for
[00:08:32.220]is the development of irregular brown-to-tan lesions
[00:08:37.905]that will develop between the leaf veins on corn leaves.
[00:08:43.230]And they're usually very irregular
[00:08:45.950]and I mean they're not perfectly rectangular,
[00:08:50.247]they may have margins that are a little bit wavy,
[00:08:53.650]and they may have a yellow discoloration.
[00:08:56.420]That seems to be pretty consistent in what we're seeing.
[00:08:59.690]So I would hold those up to the light
[00:09:02.346]and see if you can see that bright yellow discoloration
[00:09:05.010]and that might be a clue that that's what you're seeing.
[00:09:07.960]We are seeing that already in Nebraska
[00:09:10.882]and that's not uncommon.
[00:09:12.660]We've been seeing bacterial leaf streak development
[00:09:15.520]very early in the season and it can continue
[00:09:18.552]to develop and spread for the rest of the season
[00:09:22.950]as long as we have favorable conditions.
[00:09:26.040]And so I would make sure and familiarize yourself
[00:09:28.790]with that one because it can be easy to mistake that disease
[00:09:32.420]for some other common ones, like gray leaf spot.
[00:09:35.790]So, Tamra, has there been any data collected
[00:09:39.760]on what the effects of bacterial leaf streak are on yield?
[00:09:44.864]Our lab has actually been working on that
[00:09:47.580]for a couple of years now.
[00:09:49.464]The first time that we began to work on
[00:09:52.430]that impact on yield, as you can imagine,
[00:09:55.457]when you're doing research on something
[00:09:57.570]and you need to have substantial disease to see the impacts
[00:10:03.400]that you're trying to record, you don't always see that
[00:10:06.250]and that's what happened to us in 2017.
[00:10:09.650]And so I'd never felt like we had
[00:10:11.681]severe enough disease to do that.
[00:10:14.631]In 2018, we did get more severe disease
[00:10:18.669]and in fact, to the point that we needed to control
[00:10:23.192]the disease in our comparison plot.
[00:10:26.890]And so what we did was we actually made applications
[00:10:31.100]of copper bactericides and other products
[00:10:33.770]in an effort to slow it down
[00:10:35.410]because we have to have plots with little to no disease
[00:10:39.159]to compare with those that have severe disease
[00:10:42.850]to really get a good measurement
[00:10:44.940]on what that yield impact would be.
[00:10:47.840]In a nutshell, the results from our experiments
[00:10:51.310]have been inconclusive to this point
[00:10:53.607]and we don't have data to share on that yet.
[00:10:56.900]One thing I would keep in mind, though,
[00:10:58.700]is any kind of leaf disease and its impact on yield
[00:11:02.838]is going to depend on how much leaf area is lost.
[00:11:07.710]So very much like what you would expect with gray leaf spot,
[00:11:11.290]the more lesions you have, the bigger they are,
[00:11:13.287]and the more leaf area affected
[00:11:15.590]is the greater the yield impact might be.
[00:11:19.190]And so this disease will probably work similarly
[00:11:23.372]and we will certainly share results from our experiments
[00:11:27.103]as soon as we have them available.
[00:11:29.670]So you briefly talked a little bit about control.
[00:11:33.270]Bacterial leaf streak, you have the word bacterial in there.
[00:11:37.380]I'm guessing this is a lot different to control
[00:11:40.040]because it's not a fungal disease, it's a bacterial disease.
[00:11:43.227]Are there good methods to control it that are affordable?
[00:11:48.553]Well, just like you said, unfortunately,
[00:11:51.430]the foliar fungicides that we've become accustomed to using
[00:11:55.150]on fungal diseases are not effective
[00:11:58.140]at controlling this pathogen and that makes it
[00:12:01.308]even more important to get an accurate diagnosis
[00:12:04.900]if you're unsure about what is out there,
[00:12:07.470]which disease you're looking at.
[00:12:09.480]And so as far as management goes,
[00:12:12.177]we take advantage of the fact that we know this bacterium
[00:12:15.780]is surviving in infected crop debris from previous years.
[00:12:20.410]And so I would take advantage of crop rotation
[00:12:23.192]and I would also work with my seed company agronomists
[00:12:27.400]and let them know that you've got this disease
[00:12:30.370]and that you want to select a hybrid
[00:12:33.158]that is one that might have better resistance or tolerance.
[00:12:37.892]It's very difficult right now, though,
[00:12:41.050]to work with this bacterium
[00:12:42.920]and we're working with our seed company representatives
[00:12:46.860]and trying to do that and so you might not see ratings
[00:12:50.270]in our seed catalogs yet as far as this disease goes,
[00:12:54.050]but many of them have ideas on which ones
[00:12:56.490]they've seen perform better in the presence of disease.
[00:12:59.680]And so I would keep that in mind, your hybrid selection,
[00:13:04.032]but unfortunately, in the product testing
[00:13:07.110]that we've conducted to this point,
[00:13:08.950]we have not had consistent benefits
[00:13:11.500]with the use of bactericides, for instance,
[00:13:14.434]especially not with single applications.
[00:13:17.940]And we're still gonna continue to work with those
[00:13:20.823]but at the moment, we can't recommend
[00:13:23.360]any of those products for use to control this disease.
[00:13:26.840]So you would say at this time,
[00:13:28.628]hybrid selection is a better form of control
[00:13:32.050]where management for bacterial leaf streak
[00:13:34.760]rather than using a bactericide?
[00:13:37.460]Yes, definitely, that and crop rotation.
[00:13:39.914]I would give that a shot.
[00:13:42.397]So we've been talking about corn mostly
[00:13:45.374]but just seeing how wet and humid it is,
[00:13:48.400]what diseases might we be facing
[00:13:50.700]in soybeans this coming year that may be out there
[00:13:54.740]or maybe, in two to three weeks, might be more of an issue?
[00:13:59.521]Well, as we move forward,
[00:14:01.921]there's of course a number of different diseases
[00:14:05.540]in both crops that could be favored
[00:14:08.590]by wet or humid conditions
[00:14:10.990]and some of them are also dependent on temperature,
[00:14:13.870]so we'll have to watch that very closely.
[00:14:18.258]We have a number of common diseases to watch for.
[00:14:22.500]For instance, in some parts of the state,
[00:14:24.990]we've had annual problems with white mold on soybean,
[00:14:29.680]for instance, and if we have wet conditions
[00:14:33.320]and high humidity around flowering,
[00:14:35.180]we could see infection by the white mold fungus.
[00:14:38.250]And subsequent development of the white mold disease
[00:14:42.330]in the field, that's more common in our northern counties,
[00:14:45.610]but we are seeing some of it down in the southern counties
[00:14:48.390]and southeast parts of the state, too,
[00:14:50.220]all dependent on weather conditions.
[00:14:53.315]And thankfully, we do have some predictive models
[00:14:55.980]to help us anticipate that.
[00:14:58.255]Other diseases that I would watch for
[00:15:00.860]as the season moves forward would be
[00:15:03.880]if we've had warm, humid conditions,
[00:15:06.310]I would watch for frogeye leaf spot
[00:15:08.842]and that disease is becoming increasingly common
[00:15:12.926]in Nebraska and other parts of the country
[00:15:15.637]and it really depends on the conditions
[00:15:19.145]and the susceptibility of the varieties,
[00:15:22.040]how severe that might become.
[00:15:24.090]It's important, though, to know that you have that disease
[00:15:28.149]and it's especially important,
[00:15:30.510]I want everyone to understand that if you choose
[00:15:33.480]to manage that fungus with a fungicide,
[00:15:36.175]we have fungicides that work very effectively
[00:15:39.550]for that disease, but it's important
[00:15:41.860]that everyone understand that we do have
[00:15:44.050]documented fungicide resistance in states around Nebraska,
[00:15:49.220]in fact, in counties bordering Nebraska.
[00:15:52.110]It's very possible that we may have
[00:15:54.990]fungicide resistance in Nebraska
[00:15:56.820]that has not been confirmed yet.
[00:15:59.180]And so if you choose to make fungicide applications
[00:16:02.010]to control this disease, I would encourage you
[00:16:04.720]in the two, three, four weeks after that application
[00:16:08.179]to monitor disease development
[00:16:10.646]and if you don't see a reduction in disease
[00:16:16.270]or at least a slowdown of the spread of that disease,
[00:16:20.310]I would ask that you collect samples
[00:16:22.060]or let someone know so that we can test some of that tissue
[00:16:26.260]and see if you're experiencing a fungicide resistance.
[00:16:29.860]Unfortunately, the fungicide resistance
[00:16:32.320]that we are observing in other states is to the QOI,
[00:16:37.207]the quinone outside inhibitor fungicides,
[00:16:40.230]and that's the same class of products
[00:16:42.980]that we've historically called strobilurins
[00:16:46.070]and they're some of our most effective products
[00:16:48.940]at controlling this disease, but unfortunately,
[00:16:52.620]if they're used alone or repeatedly,
[00:16:54.900]you can see resistance development to them
[00:16:57.564]and it's a single site mode of action and a mutation
[00:17:01.947]and so if you develop resistance to one of them,
[00:17:05.350]you'll have resistance to all of them in that class.
[00:17:08.420]And so in that case, we always recommend the use
[00:17:11.590]of a product that has two or more products
[00:17:15.110]from different classes so that we're not forcing
[00:17:18.143]the development of resistance and that it will give you
[00:17:22.070]more adequate control of the disease.
[00:17:25.110]That's all very good information there,
[00:17:27.278]especially on strategies on how to actually keep
[00:17:30.850]our fungicide technologies effective,
[00:17:33.439]which would be using a project
[00:17:36.160]that has two different modes of action.
[00:17:38.842]Yes, two or more.
[00:17:40.540]We have a number of different products available to us now.
[00:17:43.456]So we're coming to the end of the CropWatch Podcast.
[00:17:46.848]I have some information to get out.
[00:17:49.416]The first one is that there will be
[00:17:51.600]a free field day near Carleton, Nebraska
[00:17:55.670]for a glyphosate resistant Palmer Amaranth management
[00:17:59.923]and that one will be on July 10th starting at 8:30.
[00:18:04.153]And lastly, there is the South Central
[00:18:07.590]Agricultural Laboratory field day,
[00:18:09.670]which will be Thursday, August 1st.
[00:18:11.480]With that, thank you, Tamra, for joining us today.
[00:18:14.580]Have a good growing season.
[00:18:17.022]Thanks, you too.
[00:18:19.516](upbeat music)

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Mid-season Disease in Corn and Soybean

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