Terms referring to the kernels are combination phrases grain corn, sweet corn, popcorn, indian corn etc.
The plant is a “corn plant”.
Maize is rarely used but understood most commonly as “indian maize” as interchangeable with “indian corn”.
If you don’t know the usage or type it’s common to use the general term like “corn field”.
This one is extremely difficult to fix as well. Ad companies bribe politicians with reduced price advertising for political campaigns to prevent laws being passed to regulate them.