Soybean Seedling Diseases
On this week’s CropWatch podcast Michael Sindelar is joined by Dr. Tamra Jackson-Ziems for a discussion on soybean seedling diseases. The podcast provides listeners with what to look for when scouting for a seedling disease, how to manage Pyhtium and Phythophthora, and resources to use in making disease management decisions. The podcast also addresses strategies for controlling soil borne diseases in general.
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[00:00:02.950]Welcome to CropWatch Podcast,
[00:00:05.400]a production of Nebraska Extension.
[00:00:12.130]Welcome to the CropWatch Podcast.
[00:00:13.630]I'm Michael Sindelar, a cropping systems extension educator.
[00:00:16.670]For today's CropWatch Podcast,
[00:00:18.870]we'll be talking about soybean seedling diseases.
[00:00:22.420]I'm gonna be joined today by Dr. Tamra Jackson-Ziems.
[00:00:26.800]Tamra, would you like to introduce yourself
[00:00:28.380]a little bit more and what your role at the university is?
[00:00:32.810]I've been at the university now for 14 years
[00:00:35.670]in the position of extension plant pathologist
[00:00:39.110]with responsibilities for corn diseases,
[00:00:41.950]more recently for soybean diseases too.
[00:00:45.730]And so I have statewide responsibility
[00:00:47.940]and enjoy working with all of our producers
[00:00:49.800]and crop consultants and ag business representatives.
[00:00:53.550]So we're talking about soybean seedling diseases.
[00:00:57.000]Did our problems or the problems
[00:00:58.620]that we'll be facing this year, did they start this year,
[00:01:01.020]or are we inheriting something from last year?
[00:01:04.650]There's probably a little bit of both.
[00:01:06.980]That's a complicated response.
[00:01:09.600]But there's a few things going on.
[00:01:12.250]In the last several years,
[00:01:13.590]we've probably had a few more problems
[00:01:15.820]with some of our seedling diseases,
[00:01:18.160]a few in particular like Phytophthora
[00:01:20.840]that really require some attention from us year after year.
[00:01:25.660]But this past year there were some particular problems
[00:01:29.290]during the growing season, especially during the fall,
[00:01:32.460]that actually impact us for this year.
[00:01:34.830]And so namely, there were some late season diseases
[00:01:38.410]that developed because of the extended cool wet period
[00:01:42.250]that we had during our growing season,
[00:01:45.330]and also that in other states
[00:01:47.800]where most of our soybean seed are produced,
[00:01:51.170]like in Iowa and Illinois.
[00:01:54.670]And because of the problems they experienced,
[00:01:56.890]we want to take some precaution this year
[00:01:59.050]for our own soybean seed to make sure that our producers
[00:02:02.120]don't experience additional problems this spring.
[00:02:06.010]What are we looking for, or what can we do,
[00:02:09.700]as you said, taking extra precautions with our seed?
[00:02:12.710]What do we wanna start out with seed-wise?
[00:02:14.660]I know maybe we're answering the question
[00:02:17.240]to something ahead of time,
[00:02:18.300]but sometimes it's nice to know right off the bat
[00:02:20.180]what step one would be.
[00:02:21.880]Absolutely, some of our viewers may have noticed
[00:02:25.470]that we had a CropWatch article come out in mid-February,
[00:02:28.700]I think on the 13th,
[00:02:30.560]where we talked about some early realization
[00:02:35.220]that we had some problems with soybean seed quality
[00:02:39.190]and germination rates.
[00:02:40.880]That information came to us
[00:02:42.640]from the Nebraska Crop Improvement Association,
[00:02:45.610]as well as the Illinois Crop Improvement Association
[00:02:49.080]where they released data showing
[00:02:51.290]that soybean seed germination rates were reduced
[00:02:55.420]compared to what you might normally see
[00:02:58.260]in some of those years.
[00:02:59.900]Now, some of that was the result
[00:03:01.750]of the diseases I mentioned earlier
[00:03:03.580]that came late in the season last year.
[00:03:05.880]For example, Phomopsis seed decay.
[00:03:08.200]We see a little bit of that every year,
[00:03:10.090]but in 2018 there was quite a bit more of it.
[00:03:12.830]It was more widespread.
[00:03:14.800]And unfortunately the pathogen
[00:03:16.880]that causes that can be seedborne,
[00:03:19.550]and it can affect quality in seed the following spring.
[00:03:23.990]And so that's something in particular
[00:03:26.180]we wanna make sure people are aware of.
[00:03:28.470]And although germination is not affected in all of our seed,
[00:03:33.820]there's a significant percentage that might be.
[00:03:37.220]And so for instance, as much as 70,
[00:03:40.460]excuse me, as much as 10% of our seed
[00:03:43.100]that was tested tested below 70% germination rate.
[00:03:47.670]And that would be important for our producers to know.
[00:03:50.900]And you can get that information right on the tag
[00:03:53.840]on your seed bag as an indication
[00:03:56.310]of what that seed lot tested at.
[00:03:58.980]And it is significantly less than what you were expecting,
[00:04:03.080]it might mean increasing seeding rate of that seed lot
[00:04:07.610]or considering a soybean seed treatment fungicide package.
[00:04:12.570]So what exactly would we be looking for early
[00:04:15.980]in the season, or what is conditions setting up for us
[00:04:19.380]to pay attention to and scout a little bit more for?
[00:04:25.292]A few things I think I would want
[00:04:27.570]to remind everyone about.
[00:04:29.000]And so it's important to consider the disease history
[00:04:32.950]that you've got in your field or fields.
[00:04:35.490]And it might not be the same in all of them,
[00:04:37.680]and it's important to know which disease
[00:04:40.650]or diseases you've had a problem with.
[00:04:42.990]And so for example,
[00:04:44.630]Phytophthora is probably the best example in soybean.
[00:04:48.510]Phytophthora is one of a couple of different types
[00:04:51.840]of pathogens that we call Oomycetes or water molds.
[00:04:55.700]And that means that they have to have wet conditions
[00:04:58.540]to become active.
[00:05:00.210]And the last couple of springs,
[00:05:02.290]we've had some pretty wet conditions,
[00:05:04.390]and thus we've seen more Pythium and Phytophthora.
[00:05:08.140]Well, in particular, Phytophthora can be especially damaging
[00:05:11.100]because it's not just a seedling disease.
[00:05:13.740]It can also infect older plants in the middle
[00:05:16.940]or even toward the end of the season and kill them.
[00:05:20.100]But management can start at the beginning
[00:05:22.500]or even before the season starts,
[00:05:24.270]and we are fortunate to have a number
[00:05:26.230]of different management strategies for Phytophthora.
[00:05:29.810]Phytophthora, for instance, we have resistance to that
[00:05:34.150]in our major soybean varieties that are available
[00:05:37.690]and resistance to specific races.
[00:05:40.820]And so for instance, you might have heard of Rps genes.
[00:05:44.160]That's specifically what we're referring to,
[00:05:49.600]Those are probably the two most common options
[00:05:52.470]for Rps genes.
[00:05:54.020]But they're not effective against all the races.
[00:05:56.840]And so they're also not effective immediately
[00:06:00.130]upon planting and germination.
[00:06:02.300]It takes a little bit of time, a few days to a couple weeks
[00:06:05.720]before that's going to protect the seed
[00:06:08.860]and the seedlings from Phytophthora.
[00:06:11.320]And so if Phytophthora's a really serious problem for you,
[00:06:13.800]you're also going to want
[00:06:15.360]to consider tolerance to that disease.
[00:06:18.410]And tolerance is similar to resistance,
[00:06:20.810]but it's not as effective,
[00:06:23.520]but it's effective against all the races.
[00:06:25.610]And so a combination of a resistant soybean variety
[00:06:28.280]with tolerance is probably your best bet.
[00:06:31.300]On top of that, though, we do have seed treatment fungicides
[00:06:35.200]that can do a good job against Phytophthora.
[00:06:38.660]Products containing active ingredients
[00:06:40.580]like metalaxyl, mefenoxam,
[00:06:43.040]or ethaboxam have been very effective against Phytophthora.
[00:06:47.700]But if you're going to go that route,
[00:06:49.720]just know that it'll take the higher rates of metalaxyl
[00:06:53.310]or mefenoxam to be effective against Phytophthora.
[00:06:57.610]With that said, those products that are effective
[00:07:00.670]against the Oomycetes are not effective
[00:07:03.040]against other types of soybean seedling diseases.
[00:07:07.020]And so the others that we might be concerned about
[00:07:09.980]like Rhizoctonia or Fusarium
[00:07:13.030]would require an additional seed treatment fungicide
[00:07:15.920]from a different class
[00:07:17.280]with a different mode of action to be effective.
[00:07:20.380]And much of this information is
[00:07:22.260]in our 2018 Guide for Weed, Disease, and Insect Management,
[00:07:27.070]and a couple of of those pages were highlighted
[00:07:29.440]and shared during that February 13th article.
[00:07:33.000]Looking at our seedling diseases that are out there,
[00:07:36.820]are there some that prefer wet warm conditions,
[00:07:39.860]whereas other ones require wet cold,
[00:07:41.660]or are there combinations,
[00:07:43.070]or are some of them all the above?
[00:07:46.280]Some of them are all the above, unfortunately.
[00:07:48.490]And so in general I think the cool wet conditions
[00:07:51.810]are probably higher risk than the warmer conditions.
[00:07:56.900]For instance, we know of several different Pythium species
[00:08:01.110]that infect soybean and corn too.
[00:08:04.260]We know now that some of those species
[00:08:06.250]actually prefer warmer conditions
[00:08:08.410]instead of cooler conditions, and others prefer it cooler.
[00:08:12.580]In general in the northern climates,
[00:08:15.860]we think that it's more common
[00:08:17.350]for the cooler favoring Pythium species
[00:08:20.760]to be the ones that we're dealing with.
[00:08:23.210]And so those conditions are especially ones
[00:08:26.370]that I could be concerned about,
[00:08:28.010]but anything that's going to impact
[00:08:29.900]or slow down the germination and emergence of our seed.
[00:08:34.260]And so I would keep that in mind
[00:08:36.680]and try to reduce overall stress to the seed
[00:08:39.600]to reduce the chance of seedling diseases.
[00:08:42.150]You know, one thing that I don't think I mentioned
[00:08:44.680]were the types of symptoms people can watch for
[00:08:48.000]for varied seedling diseases.
[00:08:50.210]And so the most common one would be symptoms
[00:08:54.043]that would impact plant emergence or germination,
[00:08:57.700]and so if you see skips in your stand at emergence.
[00:09:02.040]And that could happen with individual plants,
[00:09:04.680]or it could also happen with clumps in low areas
[00:09:09.180]of the field, for instance, where it was wetter longer.
[00:09:12.840]And if you see those skips,
[00:09:14.500]it's not too much work to take your spade
[00:09:17.210]or your shovel and try to dig where a seedling should be
[00:09:20.630]and see if you can find it and take a closer look at it
[00:09:23.140]and see if you have any evidence
[00:09:24.800]of rotted roots or discoloration
[00:09:28.320]that might indicate a seedling disease problem.
[00:09:33.260]Are there any symptoms that we should be looking at
[00:09:35.050]on our seedlings when they emerge for disease indications?
[00:09:39.420]Similarly, any discoloration or evidence of stunting.
[00:09:45.150]Or you might see wilting or discoloration.
[00:09:48.800]And the unfortunate part is some
[00:09:51.490]of those seedling disease symptoms are pretty fleeting.
[00:09:54.990]They're not gonna last very long.
[00:09:56.910]Some of them might kill the plant very quickly,
[00:09:59.670]and you might not have a chance to find them,
[00:10:01.340]so you may see a dead plant there in the ground.
[00:10:04.990]But not all seedling diseases necessarily kill plants.
[00:10:08.440]Some of those plants may survive.
[00:10:11.860]They may always be stunted and always be infected
[00:10:15.030]and might not compete the best versus their neighbors.
[00:10:19.450]And so I would watch for those symptoms
[00:10:22.040]and might have to make a judgment call
[00:10:24.660]if a large area of the field is affected.
[00:10:28.390]So that would be something like Phytophthora
[00:10:30.433]that may not be as obvious as a seedling,
[00:10:32.470]but you come back later in the season
[00:10:34.230]and you're starting to really see those symptoms
[00:10:36.370]throughout the plant and it makes it easier to diagnose it.
[00:10:39.770]Exactly, and there's really nothing else you can do
[00:10:42.650]later on in the season.
[00:10:43.780]We can't apply a foliar fungicide to turn that around.
[00:10:47.840]And you just need to make a mental note
[00:10:49.560]of which fields were affected.
[00:10:51.420]I really think it's a good idea to submit a sample
[00:10:54.830]to the Plant and Pest Diagnostic Clinic too for confirmation
[00:10:58.740]because many of the diseases we work with
[00:11:00.820]have very similar symptoms,
[00:11:03.030]and you wanna make sure that you know which one
[00:11:05.040]so that you can make careful selections
[00:11:07.390]of your soybean varieties,
[00:11:09.488]and that'll mean better management in the future.
[00:11:13.510]So how would rotation work in managing this disease?
[00:11:18.430]Knowing that the majority of producers here
[00:11:20.830]do a two year rotate between corn and soybeans,
[00:11:24.090]is rotation an answer?
[00:11:27.200]Well, for most diseases and most pests in general,
[00:11:30.370]we do recommend crop rotation.
[00:11:33.110]Unfortunately, the pathogens that cause seedling diseases
[00:11:36.900]are those that are soilborne, though.
[00:11:39.240]And all of them have some special spore stage
[00:11:43.600]that is a survival structure.
[00:11:45.690]It may have a thick wall.
[00:11:47.530]But it's meant to help them survive harsh conditions
[00:11:51.500]like drought and even predation
[00:11:53.740]by some invertebrate species.
[00:11:55.590]And so in general, these pathogens are gonna outsurvive
[00:11:59.893]whatever rotation that we have for them.
[00:12:02.110]And in fact, some of them can infect both corn and soybean
[00:12:05.740]or some of the other common crops we would rotate with.
[00:12:08.800]So rotation is not usually gonna be
[00:12:10.710]that beneficial for seedling diseases.
[00:12:13.540]It would also be a good idea
[00:12:15.650]to consider other ways of reducing stress
[00:12:18.380]that people might not have thought of.
[00:12:20.270]We know now that herbicide injury can actually predispose
[00:12:24.450]some of these seedlings to seedling diseases,
[00:12:26.910]and so there is a complex interaction there
[00:12:29.550]that we're just beginning to understand,
[00:12:31.870]as well as a potential impact
[00:12:33.980]on soybean cyst nematode on other diseases.
[00:12:37.570]And we knew that for sudden death syndrome, for instance,
[00:12:40.620]but it's becoming more evident
[00:12:42.440]that soybean cyst nematode can impact seedling diseases,
[00:12:45.740]and so making sure you select resistant varieties
[00:12:48.510]for SCN too may be important.
[00:12:51.737]So this would be another good year
[00:12:52.590]since the Soybean Board did fund the testing
[00:12:55.870]for soybean seed nematode
[00:12:57.910]that if you have a field that's spotty
[00:13:00.120]or you're starting to see skips,
[00:13:02.160]it may be a a good idea just to submit another free sample
[00:13:04.600]to the diagnostics lab to see
[00:13:06.020]if you may have soybean nematode.
[00:13:08.130]Absolutely, especially if your yields are not hitting
[00:13:11.660]what you're expecting them to
[00:13:12.897]and you've ruled out other causes for that.
[00:13:16.190]This being free, it's about a $20 value per location.
[00:13:19.840]And we request that you submit those
[00:13:22.180]to the Plant and Pest Diagnostic Clinic there
[00:13:24.710]at UNL on East Campus.
[00:13:26.960]All right, anything else important?
[00:13:29.990]Yes, I guess lasting comment would be
[00:13:33.240]if you are making seed treatment decisions for soybean,
[00:13:37.960]consider that the diseases that you've had in the past
[00:13:41.730]and that some of your seed coming in
[00:13:43.840]may be carrying something
[00:13:45.100]that you haven't had before like Phomopsis.
[00:13:47.630]And if you're selecting a package of seed treatments,
[00:13:51.590]make sure that the one you select also has good activity
[00:13:54.400]against Phomopsis seed decay for 2019.
[00:13:58.700]And you'd look that information up in the--
[00:14:00.600]Guide for Weed, Insect, and Disease Management.
[00:14:03.500]And if you need to purchase one or more,
[00:14:05.170]those are available through the UNL Marketplace,
[00:14:07.940]I think for $15 online.
[00:14:10.630]Thank you for sharing that with us today, Tamra.
[00:14:12.900]Absolutely, I appreciate being on here.
[00:14:14.970]Have a great growing season.
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