Controlling volunteer winter wheat helps prevent losses
By Wilma Trujillo
CSU Southeast Area Agronomist
Each year wheat growers lose potential income by not controlling volunteer wheat and other weeds on time. In southeast Colorado, the largest losses are due to viral infections (Wheat Streak Mosaic, High Plain, Triticum Mosaic, and Barley Yellow Dwarf) and soil water losses.
The greatest risk of losses from aphid- and mite-vector viruses start when volunteer wheat emerges just after harvest and creates the "green bridge." Mites and viruses survive the summer on this green bridge and move to the newly emerged wheat in the fall. After landing on a new host, mites crawl to the younger leaf and begin to feed and reproduce. Mites remain active for two to four weeks or even longer with mild temperatures.
The earlier the wheat is planted and the longer mild fall weather extends, the greater the risk of spreading wheat streak mosaic and other viral infections. Reproduction and spread of mites stop with cool temperatures. However, mites survive cold winter temperatures in the forms of eggs, nymphs and even adults in the crown of winter wheat. The viruses survive the winter within the plants. As winter wheat greens up in the spring, mites become active and continue spreading the viruses to healthy plants.
Volunteer wheat that survives the summer and fall posts numerous risks to the subsequent wheat crop as well as to other rotated crops (corn, sorghum) next year. Volunteer wheat and weeds attracts aphids, wheat stem sawfly, thus increasing the risk of yield losses. Destroying volunteer wheat and grassy weeds using herbicide or tillage, delaying seeding and planting resistant varieties are the most effective control measures again viral infections.
For more information on controlling volunteer wheat and mite populations, please contact your local Colorado State University Extension offices or visit us at http://www.ext.colostate.edu.