The Benefits Add up to Bushels of Yield and Added Income
By Robert Klein, Crops Specialist; Greg Kruger, Cropping Systems Specialist; Jeff Bradshaw, Entomologist; Stephen Wegulo, Plant Pathologist; Gary Hein, Doctor of Plant Health Professional Program; Tony Adesemoye, Plant Pathologist--University of Nebraska-Lincoln
Each year wheat producers lose millions of dollars in potential income by not controlling volunteer winter wheat and other weeds in wheat stubble. In the Central Great Plains, the largest losses are due to wheat streak mosaic and soil water losses.
By far, the greatest risk of losses from mite-vectored viruses occurs when there is a summer "green bridge" of volunteer wheat emerging before harvest. This almost always occurs as a result of wheat seed head shatter from hail storms (Figure 1).
The mites and viruses survive the summer on this "green bridge" and the mites move from volunteer wheat to newly emerged winter wheat plants in the fall, transmitting the viruses. The mite also transmits the wheat High Plains virus and the Triticum mosaic virus, creating the likelihood of some very severe mixtures of viral infections.
The mite depends entirely on the wind for dispersal. In the fall as mite populations increase, they leave the protected areas of volunteer wheat plants (rolled leaves and whorls) and crawl to leaf tips or other exposed areas where they become airborne. After landing on a new host, the mites crawl to the youngest leaf and begin to feed and reproduce.
Not controlling volunteer wheat and weeds ...
- Can cost you 30 to 100 bushels of corn or sorghum the next year.
- Can cost you or your neighbor the value of next year's winter wheat crop.
- Can make weed control more difficult and expensive in next year's crop.
- May make it more difficult to plant the next crop in last year's stubble.
- Can result in lost yield from water loss.
In heavily infested volunteer wheat, most mites will carry the virus, and transmission to the young winter wheat plants requires few mites. Immature mites acquire the virus in as little as 15 minutes as they feed on infected leaves. Mites remain active for most of their lives (two to four weeks or longer with cool temperatures), but the transmission efficiency of adult mites decreases with age.
Factors Affecting Disease Risk
The earlier winter wheat is planted and the longer mild weather extends through the fall, the greater the risk of spreading wheat streak mosaic and other viral infections. Under warm fall conditions, the probability of secondary spread of mites and virus increases, resulting in greater incidence of infection.
Reproduction and spread of the mites stop with cool temperatures in the fall; however, mites can survive cold winter temperatures. The virus survives the winter within the plant, and the mites survive as eggs, nymphs, or adults protected in the crown of the wheat plant. As winter wheat greens up in the spring, mites become active and the virus can be spread to healthy winter wheat plants or to emerging spring wheat.
One example of wheat streak severity resulted from a neighbor's hailed winter wheat crop across the road; the affected wheat crop averaged 5 to 6 bushels per acre on 320 acres. Yields in nearby areas which had not been hailed and didn't have volunteer wheat yielded 60 bu/ac.