Symptoms of Mite-transmitted Viruses in Wheat
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 demonstrates the sequential development of symptoms of these viruses as they develop in the wheat field through the season.
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[00:00:07.700]Across the Great Plains
[00:00:08.780]of the United States the wheat curl mite transmits a complex
[00:00:11.620]of three viruses to winter wheat:
[00:00:13.830]wheat streak mosaic virus,
[00:00:15.670]high plains wheat mosaic virus,
[00:00:17.940]and triticum mosaic virus.
[00:00:20.100]All three of these viruses can infect wheat plants
[00:00:22.720]at the same time but surveys have shown
[00:00:25.250]that wheat streak mosaic virus
[00:00:26.800]is the most prevalent virus of the three.
[00:00:29.690]Infection of wheat by these viruses
[00:00:31.560]results in similar symptoms.
[00:00:34.440]In winter wheat, virus symptoms generally
[00:00:36.360]do not appear until spring, after temperatures warm
[00:00:39.590]to above 75 to 80 degrees fahrenheit.
[00:00:42.990]However in the Central Great Plains,
[00:00:45.210]when fall conditions are unusually warm,
[00:00:47.880]or under the typically warm conditions
[00:00:49.840]in the Southern Great Plains, symptoms may develop
[00:00:52.797]before plants enter dormancy in the fall.
[00:00:56.240]For optimum management it is important to be able
[00:00:58.620]to identify virus symptoms in over summering volunteer wheat
[00:01:02.440]and in the developing wheat crop.
[00:01:07.810]At a larger spacial scale across the field
[00:01:10.360]there is often a gradient pattern of symptoms
[00:01:12.620]creating a border effect with the most severe yellowing
[00:01:15.780]occurring at the mite and virus source.
[00:01:19.100]However if the mite virus source is large
[00:01:21.970]and heavily infested with mites,
[00:01:23.950]this gradient may extend up to a mile or more,
[00:01:27.200]thus fields adjacent to the source
[00:01:29.370]will appear uniformly damaged.
[00:01:33.600]Symptoms of virus infection develop
[00:01:35.388]progressively on the wheat plant
[00:01:37.790]and observing this progression enables
[00:01:39.850]a more accurate diagnosis.
[00:01:42.210]The first symptoms of virus infection are subtle
[00:01:45.390]and begin with a mottling appearance
[00:01:47.350]on the uppermost leaf that is characterized
[00:01:49.540]by a mosaic pattern of light or greenish yellow
[00:01:52.850]and dark green.
[00:01:55.100]This discoloration may take on a more spotted appearance
[00:01:57.960]when more than one virus is involved.
[00:02:01.640]An additional symptom on the leaf is the tight curling
[00:02:04.606]of the leaf edge, caused by the feeding of the mites.
[00:02:08.550]As the virus develops in the plant
[00:02:10.740]the symptoms become more obvious,
[00:02:12.530]with increased yellowing of the leaves
[00:02:14.250]along the entire length of the leaf.
[00:02:17.230]As new leaves emerge on the plant
[00:02:19.040]they begin to show the more subtle mosaic
[00:02:21.320]pattern of discoloration and the older leaves
[00:02:24.350]become progressively more yellow.
[00:02:28.830]Plants infected early in the fall show more severe symptoms.
[00:02:32.670]As symptom severity increases, these early infected plants
[00:02:36.403]begin to show severe stunting and a distinct spratling
[00:02:40.370]or laying down of the tillers.
[00:02:43.140]If the level of infection is high enough
[00:02:45.100]to cause severe stunting and spratling,
[00:02:47.710]this will result in extreme yield impact.
[00:02:51.340]Plants infected later in the fall
[00:02:53.570]or the early spring may show considerable leaf yellowing
[00:02:57.200]but they will not show this severe stunting and spratling.
[00:03:01.610]By observing the progression of these symptoms
[00:03:03.740]across the wheat field and on the wheat plants,
[00:03:06.860]a positive diagnosis can be made and an accurate estimation
[00:03:11.370]of the severity and impact of this potentially devastating
[00:03:14.670]disease complex will result.
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