Good morning, Bob. 

Thank you for reaching out with your question on weed and grass killers for your sweet corn. 

In researching for answers, it would be helpful to know what stage your corn is at - if it's emerged from the ground yet and if so, how tall it is. 

Additionally, knowing the size of your corn patch and the weed types you're seeing would be good to know. Pictures are helpful but not necessary. 

I look forward to your response. 

It appears from the conversation you have sweet corn that is roughly 2 inches tall. Probably taller since its been a couple of days. 
S-metolachlor is the active ingredient in Dual II Magnum, Cinch, and Mocassin II Plus. This is herbicide along with atrazine can be applied to emerged sweet corn up to 5 inches tall. if corn is tall than 5 inches and before 12 inches it can be sprayed down the rows but not directly on the corn. Make sure to read all labels and apply according.