You may be seeing some chlorosis and necrosis (burn and dead tissue) that is related to boron toxicity. The images below are from a field sprayed recently with fungicide plus boron. On the ends of the field, where the tractor slowed and the boron was still being sprayed, is where the burn was most prominent. However, you could see occasional leaves with symptoms where the spray was delivered at the normal tractor speed. There is no issue with the level of burn in the vast majority of the field. Where the tractor slowed, those spots on the end of the field are probably injured enough to impact yield.