8 - 2020 South Central Ag Lab Field Day

Mike Kamm Author

12/04/2020 Added

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2020 South Central Ag Lab Field Day

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[00:00:04.650]Hi.
[00:00:04.910]My name is Tamra Jackson Ziems, Nebraska Extension plant pathologist,
[00:00:09.080]covering diseases of corn and grain sorghum.
[00:00:11.990]Today we're at the South Central Ag Lab in Clay County.
[00:00:14.810]And I want to talk to you about Southern Rust.
[00:00:17.750]We're mid August right now in Southern Rust has been an issue for us in various
[00:00:21.860]parts of the state all the way to the Northern regions,
[00:00:24.590]but it really started down here in the Southern counties where we see it more
[00:00:28.910]routinely. This year is worse in many of these fields.
[00:00:32.840]We're beginning to get severe Southern rust where it's more widespread in
[00:00:37.070]fields. Many of them of course have also been treated.
[00:00:40.610]And so when you're out there looking at Southern Rust, of course,
[00:00:43.520]this is a rust disease that produces a lot of orange and tan spores.
[00:00:48.470]Those spores are primarily on the top side of the leaf.
[00:00:51.800]And so you can see them here on this leaf that I've got in my hand.
[00:00:56.000]And so these spores do rub off on your fingers.
[00:00:59.300]And so you can see that orange discoloration there uniquely,
[00:01:04.280]we don't generally see Southern Rust sportive element on the backside of the
[00:01:08.570]leaf. And so that's one way we use it to help differentiate it from other rust,
[00:01:13.940]unless you see it near the mid ribs. Sometimes we see spore development there,
[00:01:18.020]or in the case of this year in 2020,
[00:01:20.750]where we've had a lot of wind damage and green snapping,
[00:01:24.320]where a lot of leaves have been flipped upside down.
[00:01:26.690]Suddenly the bottom of the leaf is the top side and that's where we've been
[00:01:30.020]seeing sporulation of course,
[00:01:32.420]many of our fungicides do a good job managing Southern Rust.
[00:01:36.290]And so timing is critical here.
[00:01:38.960]And many fungicides only give us about 21 days of
[00:01:43.430]protection.
[00:01:44.690]And so applying it too early might mean if we have a late bout with Southern
[00:01:48.950]rust,
[00:01:49.670]that's when we see the fungicide protection come to an end and we see Southern
[00:01:54.620]rust development,
[00:01:55.610]and we come to questions about whether or not we should treat this late in the
[00:01:59.510]season, late dough and getting into dent like we are now,
[00:02:03.770]we have a very slim chance of getting a return on the investment of a foliar
[00:02:07.760]fungicide. And so we have to think really hard about that.
[00:02:11.720]Some fields may be especially vulnerable.
[00:02:14.330]And so anything that's very late planted that still early in its development
[00:02:19.070]say in the milk stager early DOUGH may still benefit from some of those
[00:02:23.360]products.
[00:02:24.590]And so you really have to get out in the field and look for Southern Rust
[00:02:28.580]because it is very patchy in the field and various throughout,
[00:02:32.510]toward the end of the season, we'll see this disease continue to spread,
[00:02:36.140]especially we're seeing it now in the lower canopy,
[00:02:39.020]a weather conditions are favorable and it's warmer and human wholesale in the
[00:02:43.310]upper canopy too. I want to warn everybody.
[00:02:46.250]If you had a lot of Southern rust or any other disease,
[00:02:49.880]it might mean that standability could be impacted before harvest.
[00:02:53.960]And so it would be worth your time to spend time out in the field after
[00:02:58.580]senescence,
[00:02:59.740]checking on standability and stock strength by pushing on those plants
[00:03:04.900]and keeping track of the number that lodge is below the ear leaf,
[00:03:09.280]it would help you identify which fields may have a problem.
[00:03:12.550]You'd need to do that to at least a hundred plants or so in each field to get an
[00:03:16.810]idea which ones are Mo more vulnerable. The lodging.
[00:03:20.080]We often have high wind events late in the season prior to harvest,
[00:03:23.950]and that could put some of those fields at risk for harvest problems.
[00:03:28.180]Later on next, I want to talk about gray leaf spot,
[00:03:32.020]and that's what I'm holding here, where the rectangular lesions are.
[00:03:35.500]And you would have seen Gabby talk about that compared to what those lesions
[00:03:39.850]look like compared to bacterial leaf streak. Well,
[00:03:43.180]green leaf spot is the disease that we normally see more commonly in South
[00:03:47.290]central Nebraska, but this year that hasn't been the case.
[00:03:50.380]We've had much less gray leaf spot, mainly in the lower canopy.
[00:03:54.370]And it just has not become severe.
[00:03:56.560]Like we would normally see this time of year warm weather conditions.
[00:04:00.190]High humidity could drive that to become worse as we get closer to the end of
[00:04:04.540]the season. And so continue to look for resistant hybrids.
[00:04:09.010]And of course, foliar fungicides, if they're needed,
[00:04:11.620]can also manage that disease.
[00:04:14.140]The leaf I'm holding right now has Pfizer Derma Brown spot,
[00:04:17.860]the fungus causing this disease creates lesions that look very different,
[00:04:22.630]whether you're talking about the leaf blade or in the Mo in the mid rib,
[00:04:26.710]like we're looking at here on the leaf blade,
[00:04:29.710]it can be yellow to orange in color.
[00:04:31.690]And some people mistake it for even Southern Rust in the midrib.
[00:04:36.280]You see that it's very dark purple or even black.
[00:04:39.130]And sometimes we see those small dots, even on leaf sheets.
[00:04:43.360]This disease has not been as common this year.
[00:04:46.570]This is one that was much more common last year because of how bad the wind or
[00:04:50.590]excuse me, how much rainfall we had.
[00:04:53.530]The timing of that rainfall is critical too.
[00:04:56.350]And although if you have a susceptible hybrid with a lot of leaf area covered,
[00:05:00.520]it can cost you yield.
[00:05:02.470]The thing that I think people are beginning to mistake this disease for is
[00:05:06.250]another disease that I want to make sure that you're watching for later this
[00:05:09.760]fall, that disease is called tar spot.
[00:05:12.850]And you may have already heard about it in the corn belt East of us,
[00:05:16.330]especially over into Iowa.
[00:05:18.970]We know that tar spot is in Western Iowa so far.
[00:05:23.500]It has not been confirmed in Nebraska,
[00:05:25.570]but we expect that that disease will eventually move into our state.
[00:05:29.110]And I hope that people, especially in the Eastern most counties,
[00:05:32.950]we'll scout fields and watch for plants that have tiny black dots on
[00:05:37.450]leaps. Those tiny black dots are fungal reproductive structures.
[00:05:42.040]They produce spores that help the disease spread it's favored,
[00:05:45.970]especially by cooler conditions, wet conditions.
[00:05:49.210]And it can be when born and splashed around this is a disease we need to watch
[00:05:54.010]for. It can be devastating, the yield in severe cases.
[00:05:58.130]And they've seen up to 50% yield loss in some of the Eastern corn
[00:06:02.840]belt, not something that we think we'll see here, at least not anytime soon,
[00:06:08.120]but in States like Michigan, where they have a lot of irrigation,
[00:06:11.450]it has aggravated this disease and increased it.
[00:06:14.840]That's why we need to watch carefully for this disease.
[00:06:18.020]The fungus will over winter and it'll develop year after year in that same
[00:06:22.700]area.
[00:06:23.120]And so we want to let producers know when it moves in so that we can monitor for
[00:06:27.140]it. And eventually if fungicides are needed,
[00:06:29.870]we'll know when and where to spray additional diseases and things that you may
[00:06:34.520]confuse with tar spot as this Southern Rust matures out here,
[00:06:38.420]the spores will eventually be black,
[00:06:40.940]the fungus switches to black spores and trying to overwinter.
[00:06:44.810]And it's easy to confuse those with tar spot. In addition,
[00:06:48.800]I want to let you know too,
[00:06:49.820]the most common thing you're going to see that causes black dots is insect
[00:06:52.970]frass. And so make sure you try to rub it off. And if you can't rub it off,
[00:06:57.200]there's a chance that it could be the fungus causing tar spot.
[00:07:00.530]And please contact us in Nebraska Extension and get us a sample to the plant and
[00:07:04.130]pest diagnostic clinic. We've moved over to the soybeans now,
[00:07:08.120]and I want to talk to you about a few important diseases that we're beginning to
[00:07:11.180]see on soybean. The first one is sudden death syndrome or what we call SDS.
[00:07:16.070]And that's beginning to flare up in some of the fields in South central Nebraska
[00:07:19.880]now.
[00:07:21.020]And so the things that you'll notice first is that the upper leaves of these
[00:07:25.100]soybean plants are beginning to turn yellow. And when you look closer,
[00:07:29.540]you'll notice that the yellowing is especially between the leaf veins.
[00:07:34.640]Eventually that area will turn necrotic or Brown,
[00:07:38.780]and the entire leaves will die and eventually fall off and defoliate that plant.
[00:07:43.610]In fact, that can happen within a couple of weeks.
[00:07:45.770]That's why they call it sudden death syndrome,
[00:07:48.260]the same plants that have the leaf symptoms also have severely rotted
[00:07:52.940]roots. And so you'll find when you go down and try to pull those up,
[00:07:56.810]they probably are going to pull pretty easily because many of the lateral roots
[00:08:00.230]have rotted off. Sometimes if you look very closely,
[00:08:04.250]you may see a bright blue discoloration. If you do,
[00:08:08.750]that's almost a guarantee that what you have is SDS because the fungus causing
[00:08:12.920]that disease, sporulate bright cobalt blue.
[00:08:16.280]And sometimes we'll see that on the surface of roots,
[00:08:19.700]a few things that you need to know about SDS.
[00:08:22.940]We do have good resistance to that disease,
[00:08:25.430]and that is your number one way to manage it. In fact,
[00:08:28.490]we've seen an increase of 80% yield in the presence of SDS.
[00:08:32.960]When you select resistant varieties. In addition,
[00:08:36.350]we also have a seed treatment Allevo that has been effective against sudden
[00:08:40.700]death syndrome.
[00:08:41.990]And it's given us benefits of 20% increases in yield.
[00:08:46.790]So we recommend in severe cases,
[00:08:49.040]you can use that seed treatment product on top of selecting a resistant variety.
[00:08:54.440]In addition, when we talk about SDS,
[00:08:56.490]I want to make sure that you understand that soybean cyst nematode is
[00:09:01.350]important because it can impact sudden death syndrome development,
[00:09:05.070]making it developed both earlier and become more severe than if the nematode was
[00:09:09.420]not there.
[00:09:10.920]Nematode distribution across Nebraska is becoming increasingly widespread.
[00:09:15.870]It's important that you sample and know whether that nematode is in your field.
[00:09:20.220]We know soybean cyst nematode can cost up to 30% yield loss
[00:09:25.140]with no visible or measurable symptoms other than you'll loss itself.
[00:09:30.480]And so it's critical that we know where it's at and that we monitor the eggs per
[00:09:35.130]a hundred CCS of soil as a measure of how bad that's getting.
[00:09:40.020]The good news is soybean cyst can be managed with crop rotation to a non host
[00:09:44.820]crop, especially corn, or even with alfalfa.
[00:09:48.750]And although we do have resistant varieties for soybean cyst nematode,
[00:09:53.280]and it's important that we select those,
[00:09:56.130]remember that the nematode can adapt to the resistant variety.
[00:10:00.660]And the unfortunate part is that we are using most of our resistant varieties
[00:10:05.430]coming from the same line that's PI 88, seven 88.
[00:10:10.530]Now we know in many States, even in Nebraska,
[00:10:13.710]that nematodes are adapting to that level of resistance.
[00:10:17.220]In some States that resistance is no longer useful in Nebraska here.
[00:10:21.960]We know that at least 50% of our nematode populations can reproduce on that
[00:10:26.460]level of resistance on that type of resistance.
[00:10:29.430]It's important when you select your varieties that not only are you looking for
[00:10:34.320]resistant varieties,
[00:10:35.550]but you're also changing varieties because the nematode can adapt not just to
[00:10:39.750]the resistance, but also to the variety itself.
[00:10:42.960]And so be sure and keep those things in mind,
[00:10:46.170]as well as you have seed treatment and a mat asides that you can also use.
[00:10:50.850]And using a.
[00:10:52.500]An assortment of different combinations of these strategies will help give you
[00:10:56.790]the most favorable results against soybean cyst nematode.
[00:11:00.780]And if you're not sure if you have soybean cyst,
[00:11:03.090]but you're having a hard time meeting your, your yield goals,
[00:11:07.350]this could be something that's holding you back.
[00:11:09.780]You can sample in any crop any time of year down to about eight inches
[00:11:14.610]deep,
[00:11:15.300]and that can be processed for soybean cyst nematode to summarize.
[00:11:19.980]We've talked about a number of diseases today in both corn and soybean,
[00:11:24.270]and it's important that you review what your fields have and keep track of that
[00:11:28.530]because that'll help you make wise decisions this winter on which varieties to
[00:11:33.480]select and better position in those fields. When you come back to soybeans,
[00:11:38.040]there's other diseases, of course,
[00:11:39.390]that you should keep your eyes out on including this time of year,
[00:11:42.270]like frogeye leaf spot.
[00:11:43.860]So I encourage you to please go to graduate student Asha Monte's
[00:11:48.510]presentation on frogeye and learn more about how we've learned that we have
[00:11:52.710]fungicide in Nebraska and how that's going to change your management
[00:11:57.400]strategies for that disease.
[00:11:59.560]If you need help identifying or managing any of these diseases,
[00:12:04.030]please send a sample to the UNL plantain pest diagnostic clinic,
[00:12:07.690]or contact us in Nebraska Extension for more information,
[00:12:10.900]thank you for joining us.

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8 - 2020 South Central Ag Lab Field Day

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