Issue No. 23, Article 4/October 5, 2012
Controlling Volunteer Corn Before Fall-Seeding Small Grains
The relatively early beginning to corn harvest has provided a good environment for the emergence of volunteer corn. Emerged volunteer corn at this time of year is normally considered to be a good situation, since all the volunteer plants will winterkill. However, if a killing frost does not occur soon, they could be an impediment to farmers who would like to sow wheat this fall.
Volunteer corn plants should be controlled before sowing small grains to provide a better environment for their establishment. This control can be accomplished with preplant tillage, but what about using a herbicide to control established volunteer corn plants?
Glyphosate is very effective for controlling existing stands of sensitive corn. There is no waiting interval between application and sowing small grains, but overall control may be improved if at least 24 hours elapses between application and replanting. However, glyphosate obviously would not control existing stands of glyphosate-resistant volunteer corn, so alternative herbicides would be required. Gramoxone SL can control volunteer corn, and control tends to improve if applications are made to corn plants with at least three leaf collars. The label of Liberty indicates that a 70-day rotational interval must elapse after application, making this product an unlikely choice to control volunteer corn prior to sowing wheat.
Poast, Poast Plus, Fusion, Fusilade, Select, and Assure II are effective for controlling volunteer corn (including volunteer glyphosate-resistant corn), but each product label specifies an interval that must elapse between application and rotation to grass crops such as fall-seeded wheat. These intervals range from 30 days (Poast, Poast Plus, Select, Select Max) to 60 (Fusion, Fusilade) to as many as 120 (Assure II), making these products unlikely choices for this particular use. An exception is Targa, which does allow applications before wheat emergence. The label warns, however, that wheat injury can result if applications are made within 7 days of sowing.
If you plan to sow wheat in fields where one or more herbicides were used earlier in 2012, be sure to check the label of each herbicide applied for information on rotational intervals. Most rotational intervals are based solely on time, but for some herbicides they can be lengthened based on other factors, such as soil pH values or droughty conditions.--Aaron Hager