I don't think I would say it THAT way.  If it did not grow above 86 deg F, then corn would come to a standstill.  And we know from observation that does not happen.

My understanding is that the process of photosynthesis tops out at 86 deg F.  Photosynthesis increases until it hits 86 deg F, and then it flat-lines.  However, respiration continues to increase when temps climb above 86 deg F.  

Photosynthesis is important in the accumulation of dry matter in the plant.

Respiration is important in the cellular level to complete plant functions. 

So, when air temp is 86 deg F, you will max out the daily accumulation of dry matter. 

Incidently, the lower the nighttime air temps are, the better your accumulation of dry matter is  (to a point). 

So, higher elevations where you have warm days and cool nights should result in better yields.

At least that is my understanding.