Identifying Soybean Seedling Diseases

Don Lee Author

05/16/2016 Added

83 Plays

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For more information visit the Oomycete Disease Diagnostics website: https://ge.unl.edu/oomycete-disease-diagnostics/

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[00:00:00.000](upbeat music)
[00:00:09.220]Hi, I'm Loren Giesler, extension plant pathologist
[00:00:11.425]at the University of Nebraska, Lincoln.
[00:00:13.783]Today, we're gonna talk about identifying
[00:00:16.103]soybean seedling diseases with a special emphasis
[00:00:19.183]on those oomycete diseases that fight Phytophthora
[00:00:22.703]and Pythium diseases that are favored
[00:00:24.403]by really wet conditions.
[00:00:26.143]The first thing we're gonna want to do
[00:00:28.093]when we get into a field situation is look
[00:00:29.763]at the overall field distribution,
[00:00:31.943]and that distribution pattern for our seedling
[00:00:34.663]stand problems are gonna be very pocketed,
[00:00:37.203]typically aggregated or pocketed around
[00:00:39.623]low spots in the field for our water liking
[00:00:42.383]or loving diseases that we see with our oomycete diseases.
[00:00:45.624]We're gonna see those pockets in various areas,
[00:00:49.303]typically a low spot, for example, here today
[00:00:51.983]we've got a terrace area in a field where you can see
[00:00:54.283]that oblong area where we had standing water
[00:00:57.365]at one point, that's gone today but you can see
[00:00:59.664]the result of that injury from that seedling
[00:01:02.323]disease that's present in this field.
[00:01:05.843]The other thing we're gonna want to do once
[00:01:08.005]we get into those specific pockets in the field,
[00:01:10.943]start to look at the margin of that pocket and the edge and
[00:01:14.223]how an individual row will see that distribution pattern.
[00:01:18.624]So typically with our seedling diseases, we're gonna see
[00:01:21.483]a good uniform stand and then in those pockets
[00:01:24.913]we're gonna see thinning in the row so we're gonna see
[00:01:27.495]a reduction of those plant numbers in a per-foot basis
[00:01:31.155]and then if it's really severe, we're gonna see areas
[00:01:34.095]where we have no seed emerged, where those plants
[00:01:36.816]have succumbed to that seed decay or rot in a pre-emergent
[00:01:40.397]damping off situation and depending on when it happened,
[00:01:43.477]we may see post-emergent damping off
[00:01:45.717]where we have pockets of even dead plants in the field.
[00:01:48.557]Now let's next take a look at a little bit closer
[00:01:51.176]at that individual plant and what type of symptoms
[00:01:53.897]and distribution we're gonna see on those.
[00:01:56.117]When we're looking at the individual row
[00:01:57.917]and we're looking at plants within the row
[00:02:00.316]and those individual plants, here we can see
[00:02:02.257]an individual seedling that's dead.
[00:02:04.614]That's a post-emergence damping off, didn't get all the way
[00:02:06.934]out of the ground and then actually, on the above ground
[00:02:09.274]plant parts, many times an indication of seedling disease
[00:02:11.956]are some of the cotyledons actually burning or wilting up
[00:02:14.595]early, before we even have a first trifolate emerging,
[00:02:17.896]we're seeing those cotyledons burning off,
[00:02:20.096]and even some marginal injury or browning and yellowing
[00:02:23.456]like we see on these plants.
[00:02:25.375]Nice indication that something could
[00:02:26.956]be happening below the ground.
[00:02:28.776]So the next thing we'll do is take that plant,
[00:02:30.656]and then we'll dig that up and look at
[00:02:32.076]the distribution of any symptoms on the root.
[00:02:33.976]So we're actually digging those plants up.
[00:02:36.015]We're just gonna take that and try to get that whole
[00:02:39.096]root system so we can try to see the actual
[00:02:42.236]distribution of what's going on below ground.
[00:02:45.136]So the first one we come into is our plant that's dead.
[00:02:48.176]Or has still got some life to it, but you can see here,
[00:02:51.856]on this one it's gonna not make it,
[00:02:54.316]and we've got some brown discoloration on lower root system.
[00:02:58.036]We've got some white roots left, but again,
[00:03:00.316]that plant's gonna die because it was killed
[00:03:02.255]here at the point right below those cotyledons,
[00:03:05.936]and that one will eventually die, and you can see
[00:03:08.196]on the tip even, some brown injury on the root system.
[00:03:10.836]These other ones where we've got cotyledon injury,
[00:03:14.116]if we start to look closer into those, we can look
[00:03:17.586]at a couple things here, we can see how much
[00:03:20.067]stress was on the plant from how deep it was planted,
[00:03:23.507]we can start to look for any distribution
[00:03:25.926]on those individual roots when we're going down in there.
[00:03:29.566]So we're not seeing a lot of fibrous regrowth.
[00:03:32.327]Again, this one we don't have any cotyledons left,
[00:03:34.746]so we know that that plant is gonna be slightly stressed
[00:03:38.467]below, and we can actually see a little bit in this case of
[00:03:42.627]some just light browning on the root system with that plant.
[00:03:47.737]So the next thing would be is if we could actually
[00:03:50.187]determine if this was pythium or phytophthora.
[00:03:53.247]So when we're actually looking inside,
[00:03:55.565]do we see any symptom inside that root system
[00:03:59.687]that would suggest a possible infection by phytophthora?
[00:04:03.658]Inside we can see we've got pretty clear and healthy
[00:04:08.457]stele in the center of the root right here,
[00:04:11.717]so it's not really looking too much like a phytophthora
[00:04:16.038]problem in this particular case, and these outer roots
[00:04:20.177]where we get that browning on the root system,
[00:04:22.717]those are breaking off, but many times we'll be able
[00:04:25.318]to just take that root system and peel that off.
[00:04:29.058]You can see here how we just maintained the stele
[00:04:31.517]of that root, the center, so when we just peel that back
[00:04:34.777]we're able to just take that off, which often indicates
[00:04:38.837]that we're dealing with a pythium on the outside
[00:04:41.637]that's just starting to lightly rot the outer part of that
[00:04:44.357]root system, and then that stele is maintaining intact.
[00:04:47.517]So our next step in identifying our seedling disease problem
[00:04:50.777]would be to collect a sample and go get that field diagnosis
[00:04:54.567]confirmed in a diagnostic center or diagnostic lab
[00:04:58.057]that could use either molecular or serological
[00:05:01.117]or even culturing methods to confirm which pathogen
[00:05:03.958]we think is the cause of our problem.

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Identifying Soybean Seedling Diseases

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