Corn Seedling Diseases
In this CropWatch podcast Michael is joined by UNL Plant Pathologist Tamra Jackson-Ziems to discuss what to look for when scouting for seedling diseases in corn, including how to differentiate diseases with similar looking symptoms, and how to submit a sample to the UNL Plant and Pest Diagnostic Laboratory for identification. They also discuss how early season stressors, such as seedling diseases, can affect corn growth later in the season.
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[00:00:03.056]Welcome to CropWatch Podcast,
[00:00:05.500]a production of Nebraska Extension.
[00:00:12.600]Welcome to the CropWatch Podcast.
[00:00:14.240]I am Michael Sindelar,
[00:00:15.130]Cropping Systems Extension Educator.
[00:00:17.250]For today's CropWatch Podcast
[00:00:18.690]we'll be talking about
[00:00:20.290]corn seedling diseases.
[00:00:22.180]I'll be joined again by Doctor Tamra Jackson-Ziems.
[00:00:27.340]We already know from the previous podcasts
[00:00:29.900]your experience and your qualifications,
[00:00:32.960]so how about
[00:00:33.793]we just dive right into the meat of the subject?
[00:00:36.410]What are we looking for
[00:00:37.243]for our corn seedling diseases this year?
[00:00:40.170]Well, there is a number of seedling diseases
[00:00:42.890]that can affect corn
[00:00:44.310]much like soybean,
[00:00:46.000]albeit we don't currently have a phytosterols species
[00:00:49.330]that we are concerned about in corn,
[00:00:51.030]and so that leaves us pythium,
[00:00:53.170]fusarium and rhizoctonia.
[00:00:55.446]I think in recent years
[00:00:57.900]we've had some seedling disease activity
[00:00:59.976]probably because of the wet conditions that we've seen
[00:01:03.920]in the last two or three spring seasons,
[00:01:06.900]and the most common seedling disease so far
[00:01:09.900]has been pythium.
[00:01:11.840]So I would warn people that if we have wet conditions
[00:01:14.890]especially if they are cooler,
[00:01:16.710]that might be something that we could see again in 2019.
[00:01:20.930]What are we looking for
[00:01:22.530]for how these diseases may impact our corn?
[00:01:24.900]Is this similar to what we were discussing about soybeans
[00:01:27.680]where you start looking for skips,
[00:01:29.610]or something maybe that didn't germinate?
[00:01:34.526]there is a broad diversity of types of symptoms
[00:01:37.250]caused by any of these seedling disease.
[00:01:39.700]Unfortunately a lot of them look very similar to each other
[00:01:43.110]but in general they can affect seedlings and seed
[00:01:48.510]both before germination,
[00:01:50.700]and before emergence
[00:01:52.030]and after emergence.
[00:01:53.620]So the earliest things that you might notice
[00:01:56.860]might be skips in the stand and the field.
[00:01:59.400]And you may have individual plants that are missing
[00:02:03.100]or you may have clumps,
[00:02:05.810]small areas in the field that are affected.
[00:02:10.040]the first thing you might notice are stunted plants,
[00:02:12.970]they may be discolored or yellowed,
[00:02:15.270]you might have some legions near the soil line.
[00:02:20.800]If you see skips though
[00:02:22.150]you might need to put out the spade or the shovel
[00:02:24.670]and do a little bit of digging
[00:02:26.190]to investigate what's going on,
[00:02:27.880]to see if actually there was or wasn't a seed dropped
[00:02:32.240]in that location,
[00:02:33.700]or maybe there is a seed down there
[00:02:35.360]and it's having trouble germinating
[00:02:36.950]or it rotted in the soil which is very common.
[00:02:42.470]Most of these pathogens also cause some degree of rotting
[00:02:45.990]and so you may see legion development,
[00:02:49.080]or discoloration and rotting on those roots,
[00:02:52.420]even on the (mumbles) as it begins to emerge too.
[00:02:56.400]So there is a number of different symptoms
[00:02:59.540]that you might find.
[00:03:01.320]I don't think I would expect anyone to feel comfortable
[00:03:04.140]differentiating between these diseases
[00:03:06.630]based on the symptoms that they find in the field.
[00:03:09.340]I'm not either.
[00:03:10.850]So I would recommend
[00:03:12.140]if these are a real consistent problem for you,
[00:03:14.950]you can always get a diagnosis from
[00:03:16.710]the UNL Plant & Pest Diagnostic Clinic,
[00:03:19.600]sending a sample there to find out for sure.
[00:03:22.630]What can we do to help out the diagnostic lab?
[00:03:24.860]'Cause we talked about this from the last one,
[00:03:27.450]so this may be an important thing.
[00:03:29.410]What can we do sample wise,
[00:03:32.120]or documentations wise
[00:03:33.470]or all the above to help the plant diagnostic lab?
[00:03:36.830]I am so glad you asked because
[00:03:39.670]the quality of the diagnosis you get
[00:03:42.410]is largely dependent on the information
[00:03:44.730]that you provide to help us,
[00:03:47.070]and the quality of the plant sample too.
[00:03:50.568]Especially in the case with these seedlings,
[00:03:53.350]they are very tender and fragile,
[00:03:55.550]and they wilt down very quickly.
[00:03:57.990]In the field the difference between
[00:04:00.482]getting a good quality sample
[00:04:01.960]with fresh symptoms
[00:04:03.670]and a plant that completely dead and crispy
[00:04:06.600]may be a matter of one day.
[00:04:08.760]So collecting that sample very carefully,
[00:04:12.350]not reaping up out of the ground,
[00:04:13.970]trying to carefully dig it up
[00:04:15.420]so you get more of that root material,
[00:04:19.030]that actually helps the diagnostician, Carl Broderick
[00:04:23.510]and all of us
[00:04:24.343]looking at those samples.
[00:04:25.940]It helps us because we have more plant tissue to work with.
[00:04:28.840]So I would try to
[00:04:30.960]carefully knock off additional soil if you can,
[00:04:35.150]but no if there is any rotting on there,
[00:04:37.150]those roots attached to that are probably gonna break off.
[00:04:40.390]And these plant samples should be placed in plastic bags.
[00:04:45.100]That surprises people a lot
[00:04:47.270]because we use paper bags so often for nutrient analysis
[00:04:50.410]but plastic bags ensure that
[00:04:52.080]the plants stay fresher longer
[00:04:53.870]until they reach the diagnostic clinic,
[00:04:56.420]and that for the entire season for disease samples.
[00:05:00.210]Plastic bags are the way to go.
[00:05:03.271]I would definitely recommend submitting
[00:05:06.580]a diversity of symptoms,
[00:05:08.510]ones that are just beginning to show symptoms,
[00:05:12.430]and if you can find a continuation of those symptoms,
[00:05:17.810]all the way down to some of the dead plants.
[00:05:19.840]In general we don't recommend dead plants
[00:05:21.980]but if we have an idea of what some of those symptoms are,
[00:05:25.190]it helps us narrow down the options of
[00:05:27.540]what might have caused it.
[00:05:29.430]What I am getting from this
[00:05:30.480]and you can correct me,
[00:05:31.580]is it's good to include in our samples plants
[00:05:36.750]that are showing the symptoms that are still alive,
[00:05:40.170]healthy plants that
[00:05:41.430]so that way the person who's looking at them
[00:05:44.000]knows what healthy looks like in your field
[00:05:46.470]versus what unhealthy looks like,
[00:05:49.260]and then you are placing the dead plant
[00:05:51.670]but if you only have the dead plant
[00:05:53.640]that's not gonna help a lot.
[00:05:54.690]It's more important to have that plant that's not quite dead
[00:06:02.290]Dead plants are rot with other problems,
[00:06:05.760]they have other micro-organisms that have already infected
[00:06:08.490]and invaded them.
[00:06:09.980]They out-compete some of the pathogens
[00:06:11.810]that we are trying to find in that plant tissue.
[00:06:14.610]The second thing I would recommend too
[00:06:16.310]is to carefully describe the distribution
[00:06:21.420]And let the diagnostician know
[00:06:23.520]if those symptoms are single plants
[00:06:26.040]or they are in just low wet areas,
[00:06:29.380]are they on higher dryer knobs out in the field.
[00:06:32.860]That's very helpful.
[00:06:34.660]In addition to describing distribution in the field
[00:06:37.700]we usually try to describe
[00:06:39.080]what's going on on the specific plants themselves .
[00:06:43.900]Are their leaves affected,
[00:06:45.390]is it just the roots that you found
[00:06:47.160]or the entire plant?
[00:06:49.020]Maybe the newer plant growth is outgrowing the problem.
[00:06:52.344]What the timeline might be
[00:06:54.353]that the symptom show up very suddenly
[00:06:56.660]or maybe after a rainfall event that
[00:06:59.730]we may have experiences.
[00:07:00.740]Some of those will also be very helpful
[00:07:03.310]coming to a diagnosis.
[00:07:05.410]It's all good information.
[00:07:07.240]So your field notes are just as important as your samples
[00:07:10.710]when trying to get the diagnostic.
[00:07:16.630]We talked about some other diseases,
[00:07:18.460]what can we do to reduce the risk of the diseases
[00:07:21.520]or manage through these diseases?
[00:07:25.540]You know, I think in general
[00:07:27.590]all of us,
[00:07:28.423]all of our producers do everything they can to
[00:07:30.500]reduce stress on the crop.
[00:07:33.057]One of the things that's becoming more and more difficult
[00:07:36.580]when we have weather conditions that are not favorable
[00:07:40.503]and we've got a lot of acres to get across
[00:07:43.150]and get planted.
[00:07:44.650]A lot of times we push the envelopes, so to speak,
[00:07:47.850]and try to get out as early as we can to get started
[00:07:50.730]so we can hurry up and finish
[00:07:53.060]our yield potential depends on our planting date.
[00:07:56.320]But it is critical for a seedling disease
[00:08:00.350]to try to avoid,
[00:08:02.580]like we talked about cool wet conditions.
[00:08:05.810]That's important to us to some extent.
[00:08:08.770]Much of that I know you can't help
[00:08:10.430]especially heavy rainfall events after planting.
[00:08:14.540]Anything you can do in that case might help.
[00:08:18.640]If you have a chronically wet are of the field,
[00:08:21.620]if there is anything you might be able to do to impact
[00:08:23.930]or improve drainage,
[00:08:25.640]that can also be helpful
[00:08:27.380]but it's not practical for everyone either.
[00:08:30.220]And some of the literature has even said
[00:08:32.170]sometimes even tillage might have been helpful
[00:08:34.960]but that's definitely not practical for everyone either,
[00:08:38.200]so you have to weigh the benefits
[00:08:40.362]of some of those recommendations.
[00:08:45.740]Are there any treatments in the early season
[00:08:49.078]that can help us
[00:08:50.723]or is that money better spent later?
[00:08:54.160]Well the good news is
[00:08:55.990]almost all of our seed corn is already treated
[00:08:58.930]with a diverse package of fungicides.
[00:09:02.210]And if you start looking closely at that label
[00:09:05.820]you will notice often three
[00:09:07.170]or four different seed treatment fungicides active
[00:09:10.420]ingredients are that on there.
[00:09:12.521]They are normally form a diverse group of fungicide classes
[00:09:16.790]which is important.
[00:09:17.670]Like we talked about in the soybean podcast
[00:09:20.250]that we have a lot different types of fungi
[00:09:22.820]and fungal-like organisms that can infect,
[00:09:24.918]and it takes different types or classes fungicides
[00:09:28.440]to most effectively control those.
[00:09:31.170]You'll also see on there sometimes
[00:09:32.980]usually we have an insecticide seed treatment as well,
[00:09:36.070]and now sometimes we also have a seed treatment nematicide
[00:09:40.340]We've got a lot of things already on there
[00:09:42.540]to protect that seed.
[00:09:44.230]So the producer does not always have the choice
[00:09:47.020]or opportunity to make decisions
[00:09:49.930]about which ones are put on that seed,
[00:09:52.370]that's done for you upstream.
[00:09:54.557]In an upstream event
[00:09:56.270]before you ever see that seed.
[00:09:58.800]So that's really good news.
[00:10:00.830]And so planting date becomes an option for us to intervene
[00:10:06.520]in that plant health.
[00:10:08.560]We don't see later application doing much good.
[00:10:13.390]So folio applications are not gonna help
[00:10:16.120]with seedling diseases.
[00:10:18.320]There is more and more interest right now though
[00:10:21.600]in furrow fungicide applications at planting.
[00:10:25.454]Although many of us are doing work on that right now,
[00:10:28.840]we don't have conclusive data to tell us whether
[00:10:32.290]the in-furrow fungicides are gonna help us
[00:10:34.370]reliably impact seedling diseases and plant health.
[00:10:38.190]So we'll continue to do that work
[00:10:40.780]but just know that
[00:10:42.220]some of the active ingredients have a lot of potential
[00:10:45.010]to provide some protection
[00:10:46.970]but we've not been able to consistently show
[00:10:49.430]the benefits of it in economics.
[00:10:52.611]And so those are a couple of other things I would consider.
[00:10:56.060]So we've briefly talked about pythium, rhizoctonia
[00:11:01.825]and fusarium .
[00:11:03.020]Is there anything important about these three diseases
[00:11:06.280]or fungal diseases
[00:11:08.040]or any issues that they may bring about later in the year?
[00:11:12.512]That's a good question.
[00:11:13.840]I think it's important for everyone to understand
[00:11:16.530]that not all of the plants that are
[00:11:19.040]infected by these seedling pathogens will dies.
[00:11:22.890]Some of them will survive
[00:11:24.850]but you might notice that these plants
[00:11:28.600]may be the ones that are less thrifty.
[00:11:30.950]They might be stunted for the rest of the season
[00:11:33.640]or discolored behind the normal crop.
[00:11:37.200]It's also important to know that some of the pathogens
[00:11:40.560]especially those caused by fusarium for instance
[00:11:43.960]can also 'cause stalk rot diseases,
[00:11:46.860]sometimes even ear rot diseases too.
[00:11:49.490]And so those plants that may have been infected early,
[00:11:52.450]if they don't die
[00:11:53.283]they might be the ones that you see die later in the season.
[00:11:57.040]And may even cause some of
[00:11:58.640]the crown rot diseases that we see
[00:12:01.260]which is actually a phase of stalk-rot.
[00:12:03.660]People have been asking more and more about these plants
[00:12:05.940]that have dies suddenly late in the season.
[00:12:08.300]That's caused by fusarium.
[00:12:09.940]In the spring,
[00:12:10.773]it's often when some of those are infected.
[00:12:14.147]Is it similar to soybeans with corn
[00:12:16.843]that try and remove as much of any hardship
[00:12:21.800]on the plants as possible,
[00:12:23.040]try and avoid herbicide damage
[00:12:25.600]or injury early in the season
[00:12:27.030]is important to avoid disease and that's also probably why
[00:12:32.250]when you are talking about fusarium
[00:12:34.130]because it puts pressure and stress on the plant,
[00:12:37.230]that it causes issues
[00:12:38.590]and opens itself,
[00:12:39.423]it's more vulnerable to diseases later on in the year.
[00:12:43.673]Whatever we can do to reduce that stress.
[00:12:47.460]Some of it,
[00:12:48.293]it's out of our control,
[00:12:49.960]But if you have a herbicide for instance that may damage
[00:12:53.590]or ding your soybeans or corn,
[00:12:56.300]we know now some of that might predispose them
[00:12:58.620]to other diseases
[00:12:59.630]like some seedling diseases.
[00:13:01.090]So I would keep that in mind
[00:13:03.030]and sharing the distribution of those symptoms
[00:13:07.040]with diagnostician when you submit the samples
[00:13:09.550]also helps us determine
[00:13:11.640]if herbicide may have played a role in that
[00:13:13.876]as well as the timing.
[00:13:16.400]Thank you for sharing that with us today Tamra
[00:13:19.300]I appreciate being on here.
[00:13:20.740]Have a great growing season.
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