Wheat Curl Mite Time Machine: an animation demonstrating mite movement and virus impact
The wheat curl mite vectors three viruses to winter wheat throughout the Great Plains. This serious virus complex includes wheat streak mosaic, Triticum mosaic, and High Plains wheat mosaic viruses. This is a visual illustration demonstrating mite movement and the spatial spread of the virus.
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[00:00:05.789]This video, developed at the University
[00:00:07.645]of Nebraska, is a narrated version of an animation
[00:00:10.756]developed to illustrate wheat curl mite movement
[00:00:13.213]and virus spread.
[00:00:15.710]Wheat curl mite time machine.
[00:00:17.642]The objective of this animation is to demonstrate
[00:00:20.216]the timing and the pattern of spread of wheat curl mites
[00:00:22.968]moving from a volunteer wheat source field
[00:00:25.494]into the surrounding landscape and the impact that results
[00:00:28.827]from the mites' vectored viruses.
[00:00:31.236]This demonstration illustrates virus spread
[00:00:33.523]typical in Nebraska.
[00:00:35.531]Warmer temperatures in the fall and spring
[00:00:37.543]will increase disease symptom development
[00:00:39.923]and final yield impact.
[00:00:42.054]During the animation, the left screen will show
[00:00:44.316]mite buildup and spread through the summer and fall.
[00:00:47.173]Later, the right screen will show the spatial sphere
[00:00:50.048]of influence from the virus that will occur
[00:00:52.368]the following spring as a result of mite movement
[00:00:55.601]and virus infection the previous fall.
[00:00:59.094]In June, winter wheat is maturing.
[00:01:01.126]The color change in wheat coincides
[00:01:02.588]with the early doe stage.
[00:01:04.676]From this time until harvest, hailstorms can knock seeds
[00:01:07.970]from wheat heads, and these seeds are capable
[00:01:10.491]of germinating and resulting in pre-harvest volunteer wheat.
[00:01:14.203]If this occurs, the stage is set for the development
[00:01:17.451]of serious virus problems for the next wheat crop.
[00:01:21.554]In July, as wheat approaches harvest,
[00:01:23.522]mites move from maturing wheat to pre-harvest volunteer
[00:01:27.259]or other hosts present at that time.
[00:01:30.153]Mites cannot survive more than a day or two
[00:01:32.620]off green plants, so they must quickly find a host
[00:01:35.938]or a green bridge to survive on until emergence
[00:01:39.507]of the new wheat crop in the fall.
[00:01:41.903]Mites transmit viruses to these green bridge hosts
[00:01:45.131]and increase in population throughout the summer.
[00:01:49.220]Through the rest of the summer, mite populations
[00:01:51.758]on pre-harvest volunteer wheat build rapidly.
[00:01:54.803]Volunteer wheat will become yellow and spraddle out
[00:01:57.761]as a result of virus infection.
[00:02:00.170]Leaf curling resulting from high mite populations
[00:02:02.765]will also occur.
[00:02:05.794]In late September, newly planted wheat is emerging
[00:02:08.159]in adjacent fields.
[00:02:09.798]Mites begin to move with the wind from the pre-harvest
[00:02:12.841]volunteer wheat to this newly emerging wheat.
[00:02:16.132]The extent of this movement will depend on the size
[00:02:18.655]of the source field and the density of the volunteer
[00:02:21.572]in the source field as well as the density
[00:02:23.993]of the mites on that volunteer wheat.
[00:02:27.817]The new wheat crop is continually infested
[00:02:30.907]with mites through the fall.
[00:02:32.852]Changing wind direction through the fall
[00:02:34.893]impacts directional mite movement.
[00:02:37.400]As a result, mite movement will occur in all directions,
[00:02:40.651]but greater spread will occur in the direction
[00:02:43.292]of the prevailing winds.
[00:02:45.306]In Nebraska, this most often results in greater
[00:02:48.320]mite movement and virus spread to the southeast
[00:02:51.005]of the source field.
[00:02:52.873]Mites transmit viruses to winter wheat in the fall.
[00:02:56.063]But because of the reduced temperatures,
[00:02:58.240]few or no virus symptoms will develop.
[00:03:01.531]Symptom expression in the fall is possible
[00:03:04.239]with extreme infestations that occur early
[00:03:06.793]or with extended warm fall conditions.
[00:03:10.563]In November, winter wheat will go dormant,
[00:03:12.798]but mites and virus remain on or in the plants
[00:03:15.725]throughout the winter.
[00:03:16.893]The yellow ovals in the diagram reflect varying levels
[00:03:19.638]of virus risk from high risk, closest to the source field,
[00:03:24.583]to medium and low risk, further from the source field.
[00:03:28.094]These risk levels are based on the extent
[00:03:30.283]of mite movement from the source field
[00:03:32.108]that accumulates throughout the fall.
[00:03:35.298]Little mite and virus activity occur
[00:03:37.517]while wheat is in dormancy.
[00:03:39.505]But as temperatures begin to increase early in the spring,
[00:03:42.795]wheat resumes growth and mites become active
[00:03:45.811]and virus resumes replication.
[00:03:48.840]Warmer temperatures in the spring lead to the development
[00:03:51.814]of obvious plant symptomology.
[00:03:54.930]The majority of spring virus impact reflects
[00:03:57.931]the mite movement pattern that occurred the previous fall.
[00:04:01.994]Symptom severity in the right screen can be compared
[00:04:04.967]to the fall risk ovals shown in the left screen.
[00:04:09.781]By May, virus damage symptoms become increasingly severe,
[00:04:13.752]especially with temperatures exceeding 80 degrees.
[00:04:16.926]Severity of virus impact depends on the time of infection.
[00:04:21.149]Plants may be stunted and tillers spraddled
[00:04:23.538]or even dead if virus infection occurred early in the fall.
[00:04:27.718]Infection can spread in the spring, but because these plants
[00:04:31.384]are in more advanced growth stages,
[00:04:33.584]they are much more resistant to the virus,
[00:04:36.244]and virus impact on the plants is not nearly as great
[00:04:40.008]as early fall infections.
[00:04:44.190]As wheat moves into the heading stages,
[00:04:46.220]the extent of virus spread and impact
[00:04:48.467]will be apparent from the symptoms.
[00:04:50.996]Significant virus impact will extend in all directions
[00:04:54.499]from the source field where winter wheat is present.
[00:04:57.341]However, the greatest spread will typically be
[00:04:59.340]to the south and east of the source field
[00:05:02.097]due to the northwest prevailing winds
[00:05:04.200]that occurred last fall.
[00:05:06.112]Much like a smoke plume spreading from a fire,
[00:05:09.057]the greatest impact from the source field
[00:05:11.333]will be closest to the source.
[00:05:13.507]But significant impact can extend
[00:05:15.394]for considerable distances.
[00:05:17.814]The sphere of influence of these mite source fields
[00:05:21.237]demonstrates the importance of identifying and controlling
[00:05:24.103]pre-harvest volunteer wheat in these source fields.
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