This summer has seen a little more rain than usual for many parts of Eastern Washington. Unlike spring showers that bring May flowers, these summer rains are likely to sprout volunteer wheat in your fields. Volunteer wheat acts as a “green bridge” that allows various insects and diseases to survive from one season’s wheat crop to the next. 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.
Wheat streak mosaic virus is carried from volunteer to newly planted wheat by the wheat curl mite. These tiny, white, cigar-shaped mites are too small to be seen with the naked eye. The curl mite uses the wind to carry it to new hosts and can travel up to half a mile from volunteer wheat.
Volunteer wheat is a host for barley yellow dwarf virus and the aphids that transmit it. Volunteer can also allow stripe rust to survive until the new wheat crop emerges, resulting in early infection of the newly seeded winter wheat.
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. Hessian fly larvae attack young wheat plants near the soil line. Tillers may be stunted, aborted, and later may lodge. During heavy infestations, the entire stand may be lost.
Volunteer wheat and other weeds also use up large amounts of soil moisture. When water storage is important, such as in summer fallow, volunteer must be destroyed.
Destroying volunteer after the new wheat emerges is too late. Producers should leave enough time to have a second chance if control is incomplete. Tillage and herbicides are the two options available for volunteer control.
Tillage usually works best when plants are small and conditions are relatively warm and dry. Under these conditions, plant death is rapid, which makes tillage a better option if you have less than two weeks before winter wheat seeding begins. Glyphosate can be used to control emerged volunteer wheat and other weeds during the fallow period. However, if glyphosate is used too close to planting time, volunteer may stay green long enough to transmit diseases and insects to the new crop. Volunteer wheat that is stressed may take two weeks or more to die following a glyphosate application, so be sure to spray well before winter wheat seeding. The optimum time to treat with glyphosate is when most of the volunteer has emerged and is healthy and actively growing. Glyphosate can effectively control volunteer wheat that has tillered.