Spread of Wheat Curl Mites into Wheat: A Demonstration
The wheat curl mite vectors three viruses (wheat streak mosaic, Triticum mosaic, and High Plains wheat mosaic viruses) to winter wheat throughout the Great Plains. This video presents a field demonstration that illustrates mite movement and virus spread that was conducted at the High Plains Agricultural Lab near Sidney, Nebraska on June 21, 2018.
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[00:00:18.239]Hello, my name is Gary Hein.
[00:00:20.140]I wanna welcome you to my neighborhood.
[00:00:23.293]More about that in a little bit,
[00:00:25.117]but I wanna introduce Lindsay Overmyer.
[00:00:27.824]Lindsay's gonna give an introduction
[00:00:29.627]of what we're doing here, and then,
[00:00:32.450]hopefully, by the end of the time that you're out here,
[00:00:35.150]all this will make sense to you.
[00:00:37.740]If you don't, I really want you to ask questions,
[00:00:39.380]but we'll see what happens, so here you go.
[00:00:43.610]All right, so we work with the wheat curl mite,
[00:00:46.130]and it transmits three different viruses to wheat.
[00:00:49.320]I might be more familiar with the viruses,
[00:00:50.693]so that would be wheat streak mosaic virus,
[00:00:53.626]triticum mosaic virus, and High Plains wheat mosaic virus.
[00:00:57.990]Remember last time around?
[00:00:59.426]So, in 2017 we saw a lot of damage
[00:01:03.300]with the viruses that occurred.
[00:01:05.750]And I'm gonna take you through the sequence,
[00:01:08.401]well, steps of how that year turned out,
[00:01:11.800]so not very good for wheat streak.
[00:01:15.920]So, as the wheat is maturing,
[00:01:19.110]so as it's approaching harvest,
[00:01:21.250]the mites are increasing in numbers,
[00:01:25.050]and just as the mites are increasing in numbers,
[00:01:29.253]a hailstorm can occur.
[00:01:30.560]So we had hail in 2016, and just at that point,
[00:01:34.390]the mites are at their maximum population.
[00:01:39.780]So we have the hail that's destroying the wheat,
[00:01:42.843]and this is gonna shatter the grain onto the ground,
[00:01:46.340]so this creates pre-harvest volunteer wheat.
[00:01:49.821]So this volunteer wheat is then gonna be infested
[00:01:51.757]with the wheat curl mite as it drops to the ground,
[00:01:55.850]so it has the nice perfect host to continue the lifecycle.
[00:02:00.898]But in addition to just the hail event,
[00:02:03.950]we also had the long warm extended fall.
[00:02:09.223]Now, this created more time for the mites
[00:02:13.600]to continue to build up in that volunteer wheat,
[00:02:16.600]and then be dispersed in other wheat
[00:02:21.016]in the neighboring fields, as you'll see in a few minutes.
[00:02:25.050]So to make the perfect disease cycle,
[00:02:28.140]we have the host, which is the volunteer wheat,
[00:02:31.947]the pathogen, which is the virus
[00:02:34.180]that is gonna be that volunteer wheat,
[00:02:37.090]basically you're always gonna have the virus with the wheat,
[00:02:40.800]and you also had this warm long extended fall.
[00:02:44.280]So this created the perfect storm
[00:02:46.920]to create a great challenge for wheat streak last year.
[00:02:52.100]But how does this mite move?
[00:02:53.400]This mite continuously moves and it needs another host,
[00:02:57.150]and this is where we wanna talk about the green bridge.
[00:02:59.747]The green bridge is the time between the wheat harvest
[00:03:03.939]and then when you plant the new wheat.
[00:03:06.780]So during this time, the mite needs a new host
[00:03:10.130]to be able to continue the lifecycle
[00:03:12.090]to infest your new crop.
[00:03:14.650]So we have, obviously the primary host
[00:03:17.780]is pre-harvest volunteer wheat, but we also have corn.
[00:03:22.530]So here we have dryland corns that are drought-tolerant,
[00:03:27.580]are staying green longer,
[00:03:29.110]and this is creating an overlapping time,
[00:03:33.260]so the green, the corn is remaining green longer,
[00:03:36.530]and this is gonna coincide
[00:03:38.540]of when you're planting your new wheat crop.
[00:03:43.540]So this is where the mites gonna be in the corn,
[00:03:46.130]and then also be dispersed by the wind to your new crop.
[00:03:50.100]But in addition, there's other wheaty hosts
[00:03:52.650]that can also be, serve as the host.
[00:03:57.270]But primarily we have pre-harvest volunteer wheat,
[00:03:59.710]which is the most important host.
[00:04:03.090]And it also really depends upon the area.
[00:04:06.500]So how large your field is of that volunteer,
[00:04:11.490]as well as the density within,
[00:04:14.580]density of the wheat in that field.
[00:04:17.430]And then we have the density of the wheat curl mite.
[00:04:21.520]So if the densities, all those densities are higher,
[00:04:24.310]you're gonna have probably more risk
[00:04:26.720]with wheat streak mosaic virus.
[00:04:30.450]And here we'll see how exactly, how these mites travel,
[00:04:34.260]and understand this neighborhood approach.
[00:04:39.220]Thank you, Lindsay.
[00:04:40.350]How many of you had wheat streak problems last year?
[00:04:43.610]Anybody, few of you?
[00:04:45.670]I know there were some hellacious problems
[00:04:47.420]north of Chappell, north and east of Chappell.
[00:04:50.310]Probably the worst I've seen since 1993.
[00:04:54.433]1993, right in this area in Cheyenne County,
[00:04:57.520]I think, what was it, Karen?
[00:05:00.210]23,000 acres were tilled up
[00:05:02.240]because of complete loss to wheat streak.
[00:05:04.843]And I think that was largely continuous acres too,
[00:05:07.800]all one patch, so what we have,
[00:05:10.972]and what I've done since that time, 25 years ago,
[00:05:16.390]that 1993 experience was the reason really
[00:05:19.470]I got started working on the curl line,
[00:05:21.753]and I'm sorry to say that in 25 years,
[00:05:24.610]I haven't solved it for you.
[00:05:25.443]Know a lot more about it then we did then,
[00:05:28.503]but one thing that I've been trying to think about,
[00:05:32.650]probably the most asked question from farmers
[00:05:36.250]and others that wonder about it is, well,
[00:05:41.760]how far can these mites move?
[00:05:43.330]How far do they move?
[00:05:44.980]We've done a series of studies
[00:05:46.470]through the last number of years
[00:05:48.490]to kinda get a handle on that.
[00:05:50.605]We don't have probably everything all figured out,
[00:05:53.040]but we do have a better understanding.
[00:05:56.820]We do know that they move by mites,
[00:05:59.600]or the mites move by wind,
[00:06:02.480]so I wondered about what do we do to,
[00:06:05.400]to demonstrate kinda how mites move.
[00:06:09.610]And a number of years ago, I did this at a field day,
[00:06:13.060]I don't know if anybody was here.
[00:06:17.040]I don't know really what,
[00:06:21.390]what the best way to do it is,
[00:06:23.290]but I think it does provide an illustration
[00:06:26.110]of what's going on with the mites.
[00:06:46.880](laughing and murmuring)
[00:06:55.740]Was that part of it, Gary?
[00:07:06.010]There's one direction.
[00:07:06.896]There's one direction that smoke is blowing.
[00:07:08.710]Of course, the wind is kinda down today,
[00:07:12.010]What happens if, this is my field here.
[00:07:14.390]This is my, this is what I talked about.
[00:07:16.430]This is my neighborhood.
[00:07:18.330]If this is my field of volunteer,
[00:07:23.270]what happens through the fall?
[00:07:25.330]Now, what we've seen is that the most severe infestations
[00:07:29.490]and infections that we see in wheat streak
[00:07:31.330]occur and originate in the fall.
[00:07:36.430]Plants that are infected at a young stage,
[00:07:39.530]in the two to three-leaf stage
[00:07:42.570]or early in the tillering stage,
[00:07:44.390]they're the ones that show the greatest symptoms.
[00:07:47.200]They are the ones that lay down and straddle.
[00:07:49.810]They're the ones that look like crap
[00:07:52.710]the next spring once it warms up.
[00:07:54.900]So it really is that time period through the fall,
[00:07:58.470]but it's accumulated activity through the fall that occurs.
[00:08:08.580]Didn't have my fire extinguisher along, I guess.
[00:08:12.290]So that's the situation that we have with wheat streak.
[00:08:17.160]You get an accumulated,
[00:08:19.330]you get an accumulated activity of mites
[00:08:23.330]moving onto your original volunteer.
[00:08:25.570]Say if this was a field of volunteer,
[00:08:27.580]in this section, and look at these grain lines,
[00:08:30.560]basically as section lines, how far does that mite move?
[00:08:34.669]Well, if they're moving from this source,
[00:08:37.920]the area at greatest risk is the orange line,
[00:08:41.450]is the orange circle.
[00:08:43.210]Now, if you look at your pictures on the handout,
[00:08:48.020]on that it's marked red.
[00:08:50.530]Within that red circle is the greatest risk
[00:08:54.208]from very serious problems from wheat streak.
[00:08:58.530]Now, the next line out on the picture is yellow.
[00:09:03.560]So within that yellow is probably a moderate risk.
[00:09:07.130]And then there's a white one.
[00:09:08.820]Within that white one there's probably
[00:09:10.940]a low to moderate risk, and then maybe,
[00:09:13.010]outside of that white area, the risk is nominal.
[00:09:18.380]So that's how you gotta look at the influence of that area,
[00:09:23.400]in that the situation is such that mites will move out,
[00:09:28.550]and just like the smoke that moved out,
[00:09:31.120]if you were standing here,
[00:09:33.350]when that thing was smoking, you'd be coughing.
[00:09:36.300]You'd probably run away.
[00:09:38.150]If you were standing out here,
[00:09:42.260]you probably wouldn't be so bad.
[00:09:45.370]If you're standing way out here,
[00:09:48.040]you probably wouldn't be bothered too much by it.
[00:09:50.367]If you had asthma you'd probably wanna get out of the way,
[00:09:53.057]but again, the further away you get from that,
[00:09:56.070]and that's one thing I try to illustrate
[00:09:58.120]with the smoke is that, that smoke plume
[00:10:02.620]is pretty much the same type of thing that's emanating out
[00:10:06.850]away from that source volunteer field.
[00:10:10.050]If you're right next to it,
[00:10:12.760]the risk is gonna be very, very high.
[00:10:15.790]Now, the size of that source field,
[00:10:17.750]and the density of mites in that source field,
[00:10:19.800]will determine how far out that red circle is.
[00:10:24.320]If you've got corn,
[00:10:26.150]mites don't reproduce quite so much in corn,
[00:10:28.900]so we often see just a yellow halo around a cornfield.
[00:10:33.470]But if you've got volunteer wheat
[00:10:35.700]where the volunteer density is very high
[00:10:38.157]and the mite density in that volunteer is very high,
[00:10:41.770]that red circle can extend perhaps a mile,
[00:10:46.170]maybe two miles more out.
[00:10:49.154]And again, it all depends
[00:10:50.670]on the size of that volunteer source
[00:10:53.397]and the density of mites in that source.
[00:10:55.940]So the greater that that is,
[00:10:58.090]the further out these risk areas are,
[00:11:00.560]the sphere of influence,
[00:11:02.770]the further out that is from that source.
[00:11:06.340]So you've got your high-risk areas,
[00:11:09.010]and then you've got a low-risk area,
[00:11:11.040]and then you get outside of that area,
[00:11:13.157]you get far enough away,
[00:11:15.200]and there really is very little risk,
[00:11:18.480]but there's still a gradient that's going on.
[00:11:20.390]Just like when they have the forest fires
[00:11:23.580]in Yellowstone or whatever, in Colorado or Utah,
[00:11:27.910]or Western Wyoming, we smell 'em at the panhandle,
[00:11:32.891]'cause it causes a whole lot of problems.
[00:11:35.060]Probably not, except if you've got asthma or something,
[00:11:37.420]but we can smell 'em, so again, the further away you get,
[00:11:42.350]the lower the density is, and it's the same with mites.
[00:11:46.150]The closer you get to that source, the greater the density.
[00:11:49.660]So the highest risk is found right here.
[00:11:53.970]Now turn your sheets over, and also I guess,
[00:11:57.810]before you do that, look at the other side.
[00:11:59.950]You can see that I've got three different circles there.
[00:12:02.300]The source is the green,
[00:12:04.620]but the sources vary in size.
[00:12:06.850]Notice that if the size of the source varies,
[00:12:10.310]the size of those circles, those ovals vary as well.
[00:12:14.900]Now if you turn it over, you can see what happens
[00:12:17.850]say north of Chappell where we had a very concentrated area.
[00:12:22.320]Section after section had problems with hail,
[00:12:25.760]they had problems with volunteer.
[00:12:27.470]Not all that volunteer was extremely dense,
[00:12:30.210]but there was a whole area of dense areas
[00:12:33.845]where there was volunteer,
[00:12:36.027]and what happened was that whole area,
[00:12:38.650]I estimate that hail streak,
[00:12:40.970]probably roughly three miles by 10 miles,
[00:12:44.240]three miles wide by 10 miles long.
[00:12:46.960]That whole area acted as a single mite source,
[00:12:51.020]and the red area extended beyond that
[00:12:53.470]to areas that didn't get hail,
[00:12:55.470]that didn't have other problems,
[00:12:57.800]because the mite density inside that central area
[00:13:00.740]was high enough that it spread out.
[00:13:03.300]Just like if you had a whole bunch of fires
[00:13:05.660]burning inside that area, you go out to the edge of it,
[00:13:09.360]outside where the fires aren't burning,
[00:13:11.890]you're still gonna see the effect of the smoke.
[00:13:15.160]So again, utilizing that smoke is an illustration
[00:13:18.020]for how we think about how mites move.
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