In our research time and time again the most consistent weed control in corn is acquired with some type of two-pass approach. Indeed last summer many folks found that they needed to apply a “rescue” herbicide application after the pre-applied played out in their corn.
The problem was many found out too-late that the pre was gone and were calling asking how to control 18- to 24-inch Palmer amaranth up in their big corn.
Given the rain we (in Tennessee) typically get in March and April it is not surprising that pre applied herbicides give out well before the corn can shade the row middles. Last year, for example, in our corn weed control research at Jackson 1.5lbs/A rate of atrazine or 2 qts/A of Bicep provided about 2 to 3 weeks of residual control. Even the more robust pre applied premixes like Lexar, Corvus or even Fierce where breaking with weeds about 4 weeks after application.
Springs that have wet periods are more the norm than the exception. That is why a two-pass corn weed control program in 9 out of the last 10 years has provided more consistent weed control than reliance on a single pass. Of course this could be one of those exception years where you farm but the odds are pretty long.
As far as managing those large Palmer in large corn a combination of Halex GT plus Status or Capreno plus Status has provided >90% control. The corn height restriction for Halex GT and Status is 30” and the corn maturity restriction for Capreno and Status is 7 leaf corn.
Read more blogs from Steckel and other useful crop management advice from UT Extension specialists.