I would not spray any kind of oil until pollination is complete. The silks do not need a barrier between them and the pollen that falls from the tassel. JMHO
Thanks for that.
My grandmother used to grow a crop of fall corn and I knew she sprayed mineral oil (it was cheap) or vegetable oil (whichever she had) to prevent as much ear worm damage. They were poor and other control methods were pricey. She died before I got all the particulars of every garden thing I remember her doing.
She also used to sucker her tomato plants around the 4th of July, put rootone on them and set them out end of July for fall tomatoes. For free!