By Darren Hefty

Roundup Ready Corn was first commercialized in the United States back in 1998.  Do you remember what a big deal that was?  It was a step-change in weed management at the time, but not for the broadleaf weeds we are fighting so hard against today.  The improvement in GRASS control was the real key.  Up until that point, Accent (and several premixes containing its active ingredient, nicosulfuron) was the primary post-emerge grass control product.  It cost around $20 per acre and was labeled and semi-reliable for controlling grasses that were 1 to 2 inches tall.  Imagine the possibility of spraying Roundup to kill grass that was bigger than that for only a few dollars per acre without much risk of potential crop injury!  It’s no wonder Roundup Ready Corn quickly took over the market.
Fast forward to today: Roundup Ready Corn dominates the market, and a small but growing percentage of acres are being planted to conventional (non-Roundup) corn hybrids.  Grass control options are still markedly different.  I’ll explain.


The most popular residual herbicides being used in Roundup Ready corn are the ones with broadleaf weed control as the primary driver.  Verdict contains a low rate of Outlook plus Sharpen.  TripleFLEX contains a low rate of Harness plus Stinger and Python.  Resicore contains the active ingredients from Surpass (low rate), Callisto, and Stinger.  The key thing to remember here is in all cases a reduced rate of the grass control residual product is being used.  That’s fine when grass pressure is light and when you have Roundup coming post-emerge to clean up the escapes.  Roundup does a great job controlling most annual grasses, and at a higher rate it can do fairly well on the perennial grasses, too.


In conventional corn it’s much different.  Our best recommendation here is to use a full rate of one of the straight grass residual herbicides: Harness, Surpass, Outlook, or Dual.  Apply them with either light, shallow incorporation OR leave them on the soil surface and let rain work them in.  The key here is to get your corn up and fully canopied as quickly as possible to reduce or eliminate late escapes because the options for post-emerge control are limited.  Accent now has a corn safener and is called Accent Q.  It has come down in price, but still costs about $14 per acre.  Many farmers are trying to pick up escape grasses with a full rate of an HPPD herbicide like Bellum, Laudis, Callisto, Armezon, or Impact plus atrazine.  These are marginal at best, and not as predictable as Accent Q.


Many of the stacked trait hybrids, but not all, have tolerance to Liberty herbicide.  While Liberty is more expensive than Roundup, some farmers are choosing to use Liberty to combat Roundup-resistant weeds.  At the same time, they can do a pretty nice job on a number of grass species if using 29-32 ounces per acre.  Liberty is especially good on woolly cupgrass.  Weeds Liberty struggles with include field sandbur, yellow foxtail, and perennial grasses.


No matter which type of corn hybrid you choose, keep grass control in mind as you make your seed and crop protection plans.  While most total programs only cost 5 to 10 bushels of corn to purchase, the yield loss from even a mild grass escape can easily cost 20, and it can get a lot worse if you have heavy pressure or additional stresses.  Also, if you’re in an area with lower rainfall or in fields with medium to low levels of fertility, great grass control is even more important for you to achieve profitable yields.