We've received a few calls lately about options for killing out poor stands of corn and planting a new stand back into those areas. Most of these calls have to do with killing a Roundup Ready/LibertyLink corn variety and planting back into these fields. We don't have a lot of data on this topic, but we did conduct a few experiments several years ago (Tables 1 and 2). There's also a summary of some published results from Dr. Larry Steckel at the University of Tennessee (Table 3).

Towards the end of 2008, Select Max (clethodim) received a supplemental label for the control of poor stands of corn. This label allows for the application of Select Max at 6 fluid ounces per acre for the control of Roundup Ready corn and for replanting of the subsequent corn crop into these areas six days after application. In our research with Select Max we have observed excellent control of small (V1-V2) corn stands with this product (Table 1). As the results in Table 1 indicate, taller and more mature (V4-V5) corn stands will be harder to control with the 6 fluid ounce rate of Select Max.

Although Select Max is probably the cheapest option for eliminating poor stands of Roundup Ready corn, some growers are just not willing to wait six days before replanting corn back into their fields. Another option that allows for immediate corn replanting is Gramoxone plus Sencor or Gramoxone plus Lorox. As shown in the tables below, these combinations can provide very good control of corn as well.

Tables 1-3 also show the inconsistency in corn control with a single application of either Liberty or Gramoxone. This is due to the contact nature of both of these herbicides and the likelihood that the growing point remained below ground at the time of these applications.

Table 1.  Influence of Select Max and comparison herbicide treatments on 
corn control at two application timings (Columbia, MO 2007).

Table 2. Influence of Gramoxone combinations on corn control at two application timings (Columbia, MO 2006).

Table 3. Average control of failed RR/LL corn stands across five sites in Tennessee (Steckel et al., 2009).