MANHATTAN, Kan. - The recent wet weather through much of Kansas has caused volunteer wheat to emerge and grow rapidly, said Jim Shroyer, K-State Research and Extension crop production specialist. Wet soil conditions may keep producers out of the fields for an extended period, or result in multiple flushes emerging, making it even more difficult than usual to control the volunteer.
To protect the state's planted wheat crop, volunteer wheat must be controlled, Shroyer said.
"Volunteer wheat within a half-mile of a field that will be planted to wheat should be completely dead at least two weeks before wheat planting," he said.
Volunteer wheat that emerges during the summer and is still present when planted wheat emerges creates numerous problems for the crop. Shroyer and K-State Research and Extension entomologist, Jeff Whitworth, reviewed some of the most serious potential problems.
- Wheat streak mosaic and associated viruses - The most important threat from volunteer wheat is the wheat streak mosaic virus complex, which is carried by the wheat curl mite. In most cases, infection can be traced to a nearby field of volunteer wheat, although there are other hosts, such as corn, millet, and many annual grasses, such as yellow foxtail and prairie cupgrass. Control of volunteer is the main defense against the wheat streak mosaic virus complex.
- Hessian fly - Hessian flies survive over the summer on wheat stubble. When the adults emerge, they can infest any volunteer wheat that may be present, which will keep the Hessian fly population alive and going through the upcoming crop season.
- Barley yellow dwarf - Volunteer wheat is a host of barley yellow dwarf virus, and the greenbugs and bird cherry oat aphids which carry it. In that respect, destroying volunteer helps reduce the reservoir for the barley yellow dwarf viruses. The aphids have to pick up the BYD virus from an infected host plant first in order to become a carrier that can transmit the disease to wheat.
- Russian wheat aphid - This aphid can also infest volunteer wheat during the summer and move onto planted wheat in the fall.
Another reason to control volunteer is that volunteer and other weeds use up large amounts of soil moisture, Shroyer said. When water storage is important, such as in summer fallow, volunteer must be destroyed.
For those reasons and more, all volunteer wheat should be completely killed within a half-mile of wheat fields at least two weeks before planting, Whitworth said.
"It is important to wait two weeks after the volunteer has died before planting wheat. This will allow enough time for any insects or mites present on the volunteer wheat to leave the area or die before the new wheat emerges," the K-State entomologist said.
Destroying volunteer after the new wheat emerges is too late, he added. Producers should leave enough time to have a second chance if control is incomplete.