Many folks the past two weeks have found that they need to apply a  “layby” herbicide application to their corn.  I have gotten a number of calls from some of these folks who were dismayed that their pre applied herbicide had given out some time ago. In many cases they are reporting that they now have 18 to 24” Palmer amaranth up in their big corn.  

Given all the rain I am not surprised the pre applied herbicides had given out. 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 this spring. Indeed even the better pre applied premixes like Lexar, Corvus or even Fierce had played out about 4 weeks after application.  

I think the reason most are surprised by the quickly played out pre applied herbicides this spring is that they were still remembering last spring.  In many cases during the spring of 2012 a pre applied herbicide in corn provided season long control.  What happened last year was once the first flush of Palmer was controlled at burndown time in March there were few later flushes do to lack of rain. 

This spring is the polar opposite of last spring with the weekly heavy rains which not only rapidly degrade a herbicide but promote many flushes of weeds particularly palmer over a 6 week window now.  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.  

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.