Cover crops offer many benefits, but one thing to consider (and something that is being researched), is the potential for pest or diseases to infest or infect your crop to become increased with a cover crops. In the case of armyworm, most of the heavily infested corn crops are those planted into rye.
"Throughout my career, the most common reports of damaging infestations
of armyworms have occurred in corn when rye has been used as a cover
crop. For more information on the biology, life cycle and management of
this pest, please refer to the Department of Crop Sciences fact sheet regarding this insect. - Dr. Mike Gray, U of I Crop Sciences Entomologist.
For the latest U of I Bulletin article, please click here: http://bulletin.ipm.illinois.edu/?p=3252
Recently, Brad Kufalk and Megan Carey of Hughes Seeds, observed severe armyworm damage on corn that had been no-tilled into rye in a field near Harvard, IL. Megan sent the following pictures of the field's devastation.